Discovery of “Meteoritic” Layered Disulphides ACrS2 (A = Na, Cr, Ag) in Terrestrial Rock

Abstract

For the first time, chromium disulphides, known from meteorites, such as caswellsilverite, NaCrS2; grokhovskyite, CuCrS2; and a potentially new mineral, AgCrS2, as well as the products of their alteration, such as schöllhornite, Na0.3CrS2∙H2O, and a potentially new mineral with the formula {Fe0.3(Ba,Ca)0.2} CrS2·0.5H2O, have been found in terrestrial rock. Layered chromium disulphides were found in unusual phosphide-bearing breccia of the pyrometamorphic Hatrurim Complex in the Negev Desert, Israel. The chromium disulphides belong to the central fragment of porous gehlenite paralava cementing altered host rock clasts. The empirical formula of caswellsilverite is (Na0.77Sr0.03Ca0.01)Σ0.81(Cr3+0.79Cr4+0.18V3+0.01 Fe3+0.01)Σ0.99S2·0.1H2O, and the end-member content of NaCrS2 is 76%. It forms single crystals in altered pyrrhotite aggregates. Grokhovskyite has the empirical formula {Cu+0.84Fe3+0.10Ca0.06 Na0.01 Sr0.01Ba0.01}Σ1.03(Cr3+0.94 Fe3+0.05 V3+0.05)Σ1.00S2·0.35H2O, and the CuCrS2 end-member content is 75–80%. A potentially new Ag-bearing chromium disulphide is characterised by the composition (Ag0.89Cu0.07)Σ0.96(Cr0.98 Fe0.03V0.01Ni0.01)Σ1.04S2. Caswellsilverite, grokhovskyite and AgCrS2 form in gehlenite paralava at high temperatures (near 1000 °C) and low pressure under reducing conditions. The structure of the layered chromium disulphides, MCrS2, is characterised by the presence of hexagonal octahedral layers (CrS2)1−, between which M-sites of the monovalent cations Ag, Cu and Na set. A low-temperature alteration of the layered chromium disulphides, when schöllhornite and {Fe0.3(Ba,Ca)0.2}CrS2·0.5H2O form, is reflected in the composition and structural modification of the layer with monovalent cations, whereas the octahedral layer (CrS2)1− remains unchanged.

Full text

Citation: Galuskin, E.V.; Galuskina,
I.O.; Vapnik, Y.; Zieli´nski, G.
Discovery of “Meteoritic” Layered
Disulphides ACrS2(A= Na, Cr, Ag)
in Terrestrial Rock. Minerals 2023,13,
381. https://doi.org/10.3390/
min13030381
Academic Editor: Roman Skála
Received: 14 February 2023
Revised: 1 March 2023
Accepted: 7 March 2023
Published: 9 March 2023
Copyright: © 2023 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
minerals
Article
Discovery of “Meteoritic” Layered Disulphides ACrS2
(A= Na, Cr, Ag) in Terrestrial Rock
Evgeny V. Galuskin 1,* , Irina O. Galuskina 1, Yevgeny Vapnik 2and Grzegorz Zieli ´nski 3
1Faculty of Natural Sciences, Institute of Earth Sciences, University of Silesia, 41-200 Sosnowiec, Poland
2Department of Geological and Environmental Sciences, Ben-Gurion University of the Negev,
P.O. Box 653, Beer-Sheva 84105, Israel
3Polish Geological Institute—National Research Institute, Rakowiecka 4, 00-975 Warsaw, Poland
*Correspondence: evgeny.galuskin@us.edu.pl
Abstract:
For the first time, chromium disulphides, known from meteorites, such as caswellsil-
verite, NaCrS
2
; grokhovskyite, CuCrS
2
; and a potentially new mineral, AgCrS
2
, as well as the
products of their alteration, such as schöllhornite, Na
0.3
CrS
2·
H
2
O, and a potentially new min-
eral with the formula {Fe
0.3
(Ba,Ca)
0.2
} CrS
2·
0.5H
2
O, have been found in terrestrial rock. Layered
chromium disulphides were found in unusual phosphide-bearing breccia of the pyrometamorphic
Hatrurim Complex in the Negev Desert, Israel. The chromium disulphides belong to the central
fragment of porous gehlenite paralava cementing altered host rock clasts. The empirical formula
of caswellsilverite is (Na
0.77
Sr
0.03
Ca
0.01
)
Σ0.81
(Cr
3+0.79
Cr
4+0.18
V
3+0.01
Fe
3+0.01
)
Σ0.99
S
2·
0.1H
2
O, and the
end-member content of NaCrS
2
is 76%. It forms single crystals in altered pyrrhotite aggregates.
Grokhovskyite has the empirical formula {Cu
+0.84
Fe
3+0.10
Ca
0.06
Na
0.01
Sr
0.01
Ba
0.01
}
Σ1.03
(Cr
3+0.94
Fe
3+0.05
V
3+0.05
)
Σ1.00
S
2·
0.35H
2
O, and the CuCrS
2
end-member content is 75–80%. A potentially
new Ag-bearing chromium disulphide is characterised by the composition (Ag
0.89
Cu
0.07
)
Σ0.96
(Cr
0.98
Fe
0.03
V
0.01
Ni
0.01
)
Σ1.04
S
2
. Caswellsilverite, grokhovskyite and AgCrS
2
form in gehlenite paralava at
high temperatures (near 1000
◦
C) and low pressure under reducing conditions. The structure of the
layered chromium disulphides, MCrS
2
, is characterised by the presence of hexagonal octahedral lay-
ers (CrS
2
)
1−
, between which M-sites of the monovalent cations Ag, Cu and Na set. A low-temperature
alteration of the layered chromium disulphides, when schöllhornite and {Fe
0.3
(Ba,Ca)
0.2
}CrS
2·
0.5H
2
O
form, is reflected in the composition and structural modification of the layer with monovalent cations,
whereas the octahedral layer (CrS2)1−remains unchanged.
Keywords:
layered chromium disulfides; caswellsilverite; grokhovskyite; schöllhornite; composition;
Raman; Hatrurim Complex; Israel
1. Introduction
In the unusual phosphide-bearing breccia of the pyrometamorphic Hatrurim Complex,
discovered in 2019 in the Negev Desert, Israel [
1
], numerous crystals of caswellsilverite,
NaCrS
2
, rare grains of grokhovskyite and a potentially new mineral, AgCrS
2
, as well
as products of their alteration—schöllhornite, Na
0.3
CrS
2·
H
2
O—and a potentially new
mineral with the simplified formula {Fe
0.3
(Ba,Ca)
0.2
}CrS
2·
0.5H
2
O (thereafter referred to as
“mineral X”), were detected.
Caswellsilverite was first described in Norton County enstatite achondrite (aubrite),
Kansas, USA [
2
]. Later it was found in enstatite chondrites in Qingzhen, Guiyang, Guizhou,
China [
3
] and Yamato 691, Eastern Antarctica [
4
]; and in Northwest Africa 5217 [
5
] and
Peña Blanca Springs (USA) aubrites [
6
]. It has also been found in some other meteorites [
4
].
Al Goresy et al. [
7
] found copper-bearing caswellsilverite and cation-deficit phase with the
composition (Cu
0.35
Na
0.32
Zn
0.01
)
Σ0.68
(Cr
0.98
Fe
0.05
)
Σ1.03
S
2
in enstatite chondrites (Yamato
691 and Qingzhen). A Cu-analogue of caswellsilverite, grokhovskyite, has recently been
Minerals 2023,13, 381. https://doi.org/10.3390/min13030381 https://www.mdpi.com/journal/minerals

Minerals 2023,13, 381 2 of 20
discovered in Uakit (IIAB) iron meteorite, Buryatia [
8
,
9
], and was almost simultaneously
described in an iron meteorite from Arnhem Land, Northern Territory, Australia [
10
]. A
mineral with the composition AgCrS
2
was detected in Peña Blanca Springs aubrites, USA,
but its structure has not been investigated [
11
]. Caswellsilverite and grokhovskyite in mete-
orites are, as a rule, associated with daubréelite, FeCr
2
S
4
, and troilite or pyrrhotite. Caswell-
silverite is easily hydrated and transforms into schöllhornite, Na
0.3
CrS
2·
H
2
O [
12
], cronusite,
Ca0.2CrS2·2H2O [13] or so-called phases of A and B type ≈(Na,K)0.07–0.12 CrS2·nH2O [14].
Layered dichalcogenides of the transition metals often display interesting electrochem-
ical and magnetic properties and are widely applied in both commercial contexts and
basic research in the areas of battery chemistry, catalytic chemistry, solid state chemistry,
thermoelectric technology, optoelectronic technology, and so on [15–17].
In the present paper, we provide the results of an investigation of the layered chromium
disulfides with the common formula MCrS
2
, where M= Na, Cu, Ag, which have been found
in terrestrial rock for the first time, and the products of their low-temperature alteration as
well as associated minerals from the phosphide-bearing breccia of the Hatrurim Complex,
Israel. We also discuss the conditions and mechanisms of chromium disulphide genesis in
pyrometamorphic rock.
2. Materials and Methods
More than 200 samples of phosphide-bearing breccia with fragments of black, weakly
altered gehlenite paralava enriched in sulphides were collected during fieldwork in 2019
and 2021 from a small outcrop in the Negev Desert, Israel [
1
,
18
]. In all, five samples,
chromium disulphides, the main object of the investigation, were detected.
The morphology and chemical composition of chromium disulfides and associated
minerals were investigated using Phenom XL and Quanta 250 EDS-equipped scanning
electron microscopes (Institute of Earth Sciences, University of Silesia, Poland). The mineral
chemical composition was measured with a Cameca SX100 electron microprobe analyzer
(EMPA, Micro-Area Analysis Laboratory, Polish Geological Institute—National Research
Institute, Warsaw, Poland), WDS, accelerating voltage = 15 kV, beam current = 10–20 nA.
Natural and synthetic standards were used.
The Raman spectra of the minerals were recorded on a WITec alpha 300R Confocal
Raman Microscope (Institute of Earth Science, University of Silesia, Poland) equipped with
an air-cooled solid laser (488 nm), a CCD camera operating at
−
61
◦
C, and a monochromator
with a 600 mm
−1
grating. The power of the laser at the sample position was ~ 4–7 mW.
Integration times of 3 s with an accumulation of 20–30 scans were chosen, and the resolution
was 3 cm
−1
. The monochromator was calibrated using the Raman scattering line of a silicon
plate (520.7 cm−1).
The reflected spectra of the minerals were measured with the help of the reflectometer
Filmetrix coupled with the optical microscope Leica 2700P using objective
×
100 and Si
Filmetrix standard.
3. Occurrence
Monovalent-metal chromium disulphides have been found in phosphide-bearing
explosive breccia, forming a small vertical zone 4–5 m wide in layered hydrogrossular-
bearing rock (“low-temperature Hatrurim”) in an outcrop on the Arad-Dead Sea road,
Hatrurim Basin, Negev Desert, Israel [
1
]. Aggregates of the Fe-P(
±
C) system minerals
barringerite, Fe
2
P (P-62m,hP9), schreibersite, Fe
3
P, native iron and schreibersite–iron
eutectic are widely distributed in the explosive breccia of the pyrometamorphic Hatrurim
Complex [
1
]. V-bearing andreyivanovite, FeCrP, and V-Cr-bearing allabogdanite, Fe
2
P
(Pnma,oP12), have also been identified in this breccia [
1
]. The super-reduced character of the
phosphide association was confirmed by the discovery of osbornite [
18
], which is extremely
unusual for rocks of the Hatrurim Complex, which formed under the oxidizing conditions
of the sanidinite facies (700–1400
◦
C and low pressure) and so are mainly composed of
minerals containing trivalent iron [19].

Minerals 2023,13, 381 3 of 20
Rocks of the pyrometamorphic Hatrurim Complex (Mottled Zone), including larnite,
spurrite, and gehlenite rocks and different types of paralavas, are distributed along the
Dead Sea rift in the territories of Israel, Palestine, and Jordan [
20
–
23
]. The “Classic”
genetic hypothesis suggests that rocks of the Hatrurim Complex formed as a result of the
burning of the bitumen substance contained in sedimentary protolith [
20
]. The recently
proposed “Mud volcanos” hypothesis states that the activation of natural fires and the
pyrometamorphic transformation of sedimentary protolith occurred with the participation
of methane delivered from gas traps in the tectonically active Dead Sea rift zone [22,24].
The studied breccia consists of clasts of altered sedimentary rock transformed into
porous hydrogrossular-bearing rock with relics of high-temperature minerals (pseudowol-
lastonite, iron phosphides, and osbornite) cemented by gehlenite paralava [
1
,
18
]. As a rule,
gehlenite in paralava is intensively replaced by hydrogrossular, which blurs the boundaries
between clasts and breccia cement, where minerals of the Fe-P(
±
C) system concentrate
(Figure 1a,b). The rounded aggregates of minerals of the Fe-P(
±
C) system exhibit a charac-
teristic zonation from the centrum to the rim (barringerite—schreibersite—schreibersite–
iron eutectic) [
1
] or schreibersite–iron (
±
cohenite) eutectic with relatively large iron segrega-
tions featuring rare schreibersite inclusions (Figure 1c). In the schreibersite–iron (+cohenite)
eutectic, small drops of native copper (Figure 1d) and daubréelite inclusions (Figure 1e)
can be observed. Aggregates of the Fe-P(
±
C) system minerals intergrow with pyrrhotite
with the lamellar exsolution structure of daubréelite (Figure 1f).
Minerals 2023, 13, x FOR PEER REVIEW 3 of 21
phosphide association was confirmed by the discovery of osbornite [18], which is ex-
tremely unusual for rocks of the Hatrurim Complex, which formed under the oxidizing
conditions of the sanidinite facies (700–1400 °C and low pressure) and so are mainly com-
posed of minerals containing trivalent iron [19].
Rocks of the pyrometamorphic Hatrurim Complex (Mottled Zone), including larnite,
spurrite, and gehlenite rocks and different types of paralavas, are distributed along the
Dead Sea rift in the territories of Israel, Palestine, and Jordan [20–23]. The “Classic” genetic
hypothesis suggests that rocks of the Hatrurim Complex formed as a result of the burning
of the bitumen substance contained in sedimentary protolith [20]. The recently proposed
“Mud volcanos” hypothesis states that the activation of natural fires and the pyrometa-
morphic transformation of sedimentary protolith occurred with the participation of me-
thane delivered from gas traps in the tectonically active Dead Sea rift zone [22,24].
The studied breccia consists of clasts of altered sedimentary rock transformed into
porous hydrogrossular-bearing rock with relics of high-temperature minerals
(pseudowollastonite, iron phosphides, and osbornite) cemented by gehlenite paralava
[1,18]. As a rule, gehlenite in paralava is intensively replaced by hydrogrossular, which
blurs the boundaries between clasts and breccia cement, where minerals of the Fe-P(±C)
system concentrate (Figure 1a,b). The rounded aggregates of minerals of the Fe-P(±C) sys-
tem exhibit a characteristic zonation from the centrum to the rim (barringerite—schreiber-
site—schreibersite–iron eutectic) [1] or schreibersite–iron (±cohenite) eutectic with rela-
tively large iron segregations featuring rare schreibersite inclusions (Figure 1c). In the
schreibersite–iron (+cohenite) eutectic, small drops of native copper (Figure 1d) and
daubréelite inclusions (Figure 1e) can be observed. Aggregates of the Fe-P(±C) system
minerals intergrow with pyrrhotite with the lamellar exsolution structure of daubréelite
(Figure 1f).
Figure 1.
(
a
) Polished fragment of breccia, on the boundary of altered country rock clasts (brown
hue) and hydrated gehlenite paralava (grey) there is a large amount of mineral aggregate of the Fe-
P(
±
C) system (white). (
b
) Polished breccia fragment with black weakly altered gehlenite paralava.

Minerals 2023,13, 381 4 of 20
(
c
) Aggregates of Fe-P(
±
C) system minerals on the boundary of paralava and altered country rock
(schreibersite and barringerite, cream; native iron (
±
cohenite), white; pyrrhotite replaced for iron
hydroxides, light-grey); reflected light. (
d
) Schreibersite (cream); native iron (white) (
±
cohenite,
white with yellow hue) eutectic with native copper inclusions, rare very small daubréelite in-
clusions are light-grey; dark points, empties; reflected light. (
e
) Schreibersite–iron eutectic with
daubréelite inclusions; BSE. (
f
) Schreibersite–iron (+cohenite) eutectic with pyrrhotite inclusion con-
taining daubréelite lamellas; optical image with high contrast. Coh = cohenite; Cu = native copper;
Dbr = daubréelite; Fe = native iron; Pyh = pyrrhotite; Scb = schreibersite.
Weakly altered paralava is black (Figure 1b). In massive fragments, native iron inclusions
are predominant (Figure 2a), whereas, in porous fragments, sulphides prevail (Figure 2b).
Altered sulphide aggregates contain calwellsilverite crystals (Figure 2c,d). Paralava with
native iron is least altered and is represented by flamite (
α
‘-Ca
2
SiO
4
)–gehlenite rock, in
which only a small proportion of flamite is replaced by rankinite, Ca
3
Si
2
O
7
(Figure 2a).
Porous paralava is predominantly composed of rankinite–gehlenite and features rare flamite
relics and prismatic pseudowollastonite crystals (Figure 2b). The main accessory minerals
in gehlenite paralava are Cr-Si-bearing perovskite, with the mean empirical formula being
(Ca
0.97
Na
0.02
Sr
0.01
)
Σ1.00
(Ti
4+0.78
Si
0.11
Cr
3+0.04
V
3+0.03
Al
0.03
Mg
0.01
)
Σ1.00
O
2.93
, chromite with the
formula (Fe
2+0.78
Mg
0.22
Ca
0.03
Mn
2+0.01
Zn
0.01
)
Σ1.05
(Cr
3+1.59
Al
0.16
V
3+0.10
Ti
4+0.08
Si
0.01
)
Σ1.94
O
4
,
Cr-V-bearing pyrrhotite and fluorapatite.
Minerals 2023, 13, x FOR PEER REVIEW 4 of 21
Figure 1. (a) Polished fragment of breccia, on the boundary of altered country rock clasts (brown
hue) and hydrated gehlenite paralava (grey) there is a large amount of mineral aggregate of the Fe-
P(±C) system (white). (b) Polished breccia fragment with black weakly altered gehlenite paralava.
(c) Aggregates of Fe-P(±C) system minerals on the boundary of paralava and altered country rock
(schreibersite and barringerite, cream; native iron (±cohenite), white; pyrrhotite replaced for iron
hydroxides, light-grey); reflected light. (d) Schreibersite (cream); native iron (white) (±cohenite,
white with yellow hue) eutectic with native copper inclusions, rare very small daubréelite inclusions
are light-grey; dark points, empties; reflected light. (e) Schreibersite–iron eutectic with daubréelite
inclusions; BSE. (f) Schreibersite–iron (+cohenite) eutectic with pyrrhotite inclusion containing
daubréelite lamellas; optical image with high contrast. Coh = cohenite; Cu = native copper; Dbr =
daubréelite; Fe = native iron; Pyh = pyrrhotite; Scb = schreibersite.
Weakly altered paralava is black (Figure 1b). In massive fragments, native iron inclu-
sions are predominant (Figure 2a), whereas, in porous fragments, sulphides prevail (Fig-
ure 2b). Altered sulphide aggregates contain calwellsilverite crystals (Figure 2c,d). Para-
lava with native iron is least altered and is represented by flamite (α‘-Ca2SiO4)–gehlenite
rock, in which only a small proportion of flamite is replaced by rankinite, Ca3Si2O7 (Figure
2a). Porous paralava is predominantly composed of rankinite–gehlenite and features rare
flamite relics and prismatic pseudowollastonite crystals (Figure 2b). The main accessory
minerals in gehlenite paralava are Cr-Si-bearing perovskite, with the mean empirical for-
mula being (Ca0.97Na0.02Sr0.01)Σ1.00(Ti4+0.78Si0.11Cr3+0.04V3+0.03Al0.03 Mg0.01)Σ1.00O2.93, chromite with
the formula (Fe2+0.78Mg0.22Ca0.03Mn2+0.01Zn0.01)Σ1.05 (Cr3+1.59Al0.16V3+0.10Ti4+0.08 Si0.01)Σ1.94O4, Cr-V-
bearing pyrrhotite and fluorapatite.
Figure 2. (a) Weakly altered massive gehlenite–flamite rock with native iron inclusions; BSE. In the
inset, polished sample of gehlenite paralava, where fragments magnified in Figure 2a,b are shown.
(b) Fragment of porous gehlenite–rankinite paralava enriched in sulphides with single prismatic
pseudowollastonite crystals, cuspidine and flamite relics; BSE. (c) Pyrite and goethite aggregates
with сaswellsilverite crystals; BSE image. (d) Caswellsilverite crystals replaced by schöllhornite and
“mineral Х”. Csp = cuspidine; Cws = сaswellsilverite; Gh = gehlenite; Gth = goethite; Fe = native iron;
Flm = flamite; Prv = perovskite; Pwo = pseudowollastonite; Py = pyrite; Rnk = rankinite; Slh =
schöllhornite; X = “mineral X”.
4. Chromium Disulphides
Caswellsilverite forms prismatic crystals, which are usually partially or completely
replaced by “mineral X” (Figure 3a,b). Caswellsilverite crystals are grey and exhibit pro-
nounced bireflectance (Figure 3c,d). Their reflectance varies from 21.8% to 31.0% (Figure
4, Table 1). The chemical composition of caswellsilverite (Figure 3b; Table 2) is
Figure 2.
(
a
) Weakly altered massive gehlenite–flamite rock with native iron inclusions; BSE. In the
inset, polished sample of gehlenite paralava, where fragments magnified in Figure 2a,b are shown.
(
b
) Fragment of porous gehlenite–rankinite paralava enriched in sulphides with single prismatic
pseudowollastonite crystals, cuspidine and flamite relics; BSE. (
c
) Pyrite and goethite aggregates
with caswellsilverite crystals; BSE image. (
d
) Caswellsilverite crystals replaced by schöllhornite and
“mineral X”. Csp = cuspidine; Cws = caswellsilverite; Gh = gehlenite; Gth = goethite; Fe = native iron;
Flm = flamite; Prv = perovskite; Pwo = pseudowollastonite; Py = pyrite; Rnk = rankinite;
Slh = schöllhornite; X = “mineral X”.
4. Chromium Disulphides
Caswellsilverite forms prismatic crystals, which are usually partially or completely
replaced by “mineral X” (Figure 3a,b). Caswellsilverite crystals are grey and exhibit
pronounced bireflectance (Figure 3c,d). Their reflectance varies from 21.8% to 31.0%
(Figure 4, Table 1). The chemical composition of caswellsilverite (Figure 3b; Table 2)
is characterised by a Na deficit compared with the ideal formula, and the mineral prob-
ably contains a small amount of water. Its empirical formula is (Na
0.77
Sr
0.03
Ca
0.01
)
Σ0.81
(Cr
3+0.79
Cr
4+0.18
V
3+0.01
Fe
3+0.01
)
Σ0.99
S
2·
0.1H
2
O (end-member content NaCrS
2
= 76%). The

Minerals 2023,13, 381 5 of 20
calculated formula of “mineral X”, which forms a thin rim on caswellsilverite (Figure 3b),
has a ratio of Cr/S
≈
1:2 and has an unbalanced charge (4.51+/4
−
). Its empirical formula
is {(Fe
3+0.24
Si
0.04
Al
0.01
)(Ba
0.12
Ca
0.10
Na
0.05
Sr
0.03
Zn
0.01
)}
Σ0.60
(Cr
3+0.99
V
3+0.02
)
Σ1.01
S
2·
0.74H
2
O
(Table 2). The chemical elements occupying sites between the disulphide layers (CrS
2
)
1−
are those in curly brackets. Here, it should be emphasised that because of the small size
of chromium disulphide grains, microprobe measurements were performed at a small
beam size of 1–2
µ
m, which could lead to sodium and water loss in the course of an
experiment. Grokhovskyite forms exsolution lamellas in twinned pyrrhotite grains with
a composition of (Fe
0.85
Cr
0.02
V
0.02
Ca
0.01
)
Σ0.90
S located at the wall of a gaseous channel
(Figure 5). Grokhovskyite lamellas are intensively replaced by secondary undiagnosed
Cr-bearing sulphates (Figure 5), as can be clearly seen in the X-Ray maps
(Figure 6, Table 3). Grokhovskyite has unbalanced charge (4.31+/4
−
) and the empirical for-
mula {Cu
+0.84
Fe
3+0.10
Ca
0.06
Na
0.01
Sr
0.01
Ba
0.01
}
Σ1.03
(Cr
3+0.94
Fe
3+0.05
V
3+0.01
)
Σ1.00
S
2·
0.35H
2
O
(Table 3). This is probably connected with its partial substitution by “mineral X”. Addition-
ally, it cannot be ruled out that a pyrrhotite matrix can affect the results of the grochowskiite
composition (Figure 5b). Nevertheless, 75%–80% of the content is the end-member CuCrS
2
.
“Mineral X”, replacing the grokhovskyite plate (Figure 5b), is characterised by the empirical
formula (charge 4.66+/4
−
): {(Fe
3+0.39
Al
0.01
Si
0.01
)(Ca
0.08
Cu
+0.05
Ba
0.05
Sr
0.04
K
0.02
Na
0.01
)}
Σ0.66
(Cr
3+0.86
Fe
3+0.13
V
3+0.01
)
Σ1.00
S
2·
0.79H
2
O (Table 3). In this cavity of paralava, there is
pyrrhotite (Fe
0.85
Cr
0.03
V
0.02
)
Σ0.9
S with intergrowths of a totally replaced chromium disul-
phide plate (grokhovskyite?) (Figure 5a–c). Interestingly, in this altered sulphide aggregate,
it was possible to detect caswellsilverite crystal partially replaced by “mineral X” and
relics of a mineral of the djerfisherite group—Ba-bearing gmalimite, (K,Ba)
6
(Fe,Cu,Ni)
25
S
27
(Figure 5d). The chemical composition of “mineral X” from pseudomorph after grokhovskyite
has the empirical formula (charge 4.3+/4
−
): {(Fe
3+0.29
Si
0.01
)(Ba
0.08
Ca
0.05
Mn
2+0.02
Sr
0.02
K
0.01
Zn
0.01
Cu
2+0.01
Na
0.01
)}
Σ0.51
(Cr
3+0.95
Fe
3+0.04
V
3+0.01
)
Σ1.00
S
2·
0.48H
2
O (Table 3).
Grokhovskyite exhibits a strong bireflectance, and its reflectance varies between 27.2 and
33.0% (Tabel 1; Figure 6a,b). Grokhovskyite was also detected as thin rims on caswellsilver-
tite crystals replaced by “mineral X” (Figure 7).
Minerals 2023, 13, x FOR PEER REVIEW 6 of 21
Figure 3. (a,b) Prismatic сaswellsilverite crystals in sulphide aggregate; BSE. (c,d) Caswellsilverite
is characterised by strong bireflectance reflected light: (c) parallel to polarizer; (d) perpendicular to
polarizer. Cws = сaswellsilverite; Gh = gehlenite; Prv = perovskite; Pwo = pseudowollastonite; Py =
piryte; X = “mineral X”
Figure 4. Reflectance spectra of chromium disulphides and pyrrhotite from gehlenite paralava. The
approximate orientation of crystals during measurements is shown by rectangles on the right side
of the figure.
Table 1. Reflectance of pyrrhotite (Pyh), schöllhornite (Slh), caswellsilverite (Cws), AgCrS2 (Ag),
“mineral X” (MinX) and grokhovskyite (Ghy) measured in random sections parallel (II), perpendic-
ular (pr) and at an angle (X) to the elongation of lamellar crystal.
nm Pyh_II Pyh_pr Slh_II Slh_pr Cws_II Cws_pr Ag_II Ag_pr MinX_II MinX_pr Ghy_II Ghy_X Chy_pr
400 29.5 27.0 19.0 23.8 21.8 28.9 23.5 25.2 26.6 29.1 27.2 27.2 27.8
420 30.5 28.0 20.2 24.9 22.3 30.0 24.9 26.5 26.2 30.0 28.2 28.2 29.0
440 31.6 29.0 22.0 25.8 23.0 31.0 26.0 28.0 26.0 30.6 29.2 29.8 30.7
460 33.0 30.0 23.8 26.9 23.6 32.0 27.2 29.5 25.0 31.0 30.0 30.9 32.0
470 (COM) 34.0 30.3 24.8 27.3 24.0 32.4 28.0 30.2 25.5 31.1 30.2 31.1 32.8
Figure 3.
(
a
,
b
) Prismatic caswellsilverite crystals in sulphide aggregate; BSE. (
c
,
d
) Caswellsilverite
is characterised by strong bireflectance reflected light: (
c
) parallel to polarizer; (
d
) perpendicular
to polarizer. Cws = caswellsilverite; Gh = gehlenite; Prv = perovskite; Pwo = pseudowollastonite;
Py = piryte; X = “mineral X”.

Minerals 2023,13, 381 6 of 20
Minerals 2023, 13, x FOR PEER REVIEW 6 of 21
Figure 3. (a,b) Prismatic сaswellsilverite crystals in sulphide aggregate; BSE. (c,d) Caswellsilverite
is characterised by strong bireflectance reflected light: (c) parallel to polarizer; (d) perpendicular to
polarizer. Cws = сaswellsilverite; Gh = gehlenite; Prv = perovskite; Pwo = pseudowollastonite; Py =
piryte; X = “mineral X”
Figure 4. Reflectance spectra of chromium disulphides and pyrrhotite from gehlenite paralava. The
approximate orientation of crystals during measurements is shown by rectangles on the right side
of the figure.
Table 1. Reflectance of pyrrhotite (Pyh), schöllhornite (Slh), caswellsilverite (Cws), AgCrS2 (Ag),
“mineral X” (MinX) and grokhovskyite (Ghy) measured in random sections parallel (II), perpendic-
ular (pr) and at an angle (X) to the elongation of lamellar crystal.
nm Pyh_II Pyh_pr Slh_II Slh_pr Cws_II Cws_pr Ag_II Ag_pr MinX_II MinX_pr Ghy_II Ghy_X Chy_pr
400 29.5 27.0 19.0 23.8 21.8 28.9 23.5 25.2 26.6 29.1 27.2 27.2 27.8
420 30.5 28.0 20.2 24.9 22.3 30.0 24.9 26.5 26.2 30.0 28.2 28.2 29.0
440 31.6 29.0 22.0 25.8 23.0 31.0 26.0 28.0 26.0 30.6 29.2 29.8 30.7
460 33.0 30.0 23.8 26.9 23.6 32.0 27.2 29.5 25.0 31.0 30.0 30.9 32.0
470 (COM) 34.0 30.3 24.8 27.3 24.0 32.4 28.0 30.2 25.5 31.1 30.2 31.1 32.8
Figure 4.
Reflectance spectra of chromium disulphides and pyrrhotite from gehlenite paralava. The
approximate orientation of crystals during measurements is shown by rectangles on the right side of
the figure.
Table 1.
Reflectance of pyrrhotite (Pyh), schöllhornite (Slh), caswellsilverite (Cws), AgCrS
2
(Ag),
“mineral X” (MinX) and grokhovskyite (Ghy) measured in random sections parallel (II), perpendicular
(pr) and at an angle (X) to the elongation of lamellar crystal.
nm Pyh_II Pyh_pr Slh_II Slh_pr Cws_II Cws_pr Ag_II Ag_pr MinX_II MinX_prGhy_II Ghy_X Chy_pr
400 29.5 27.0 19.0 23.8 21.8 28.9 23.5 25.2 26.6 29.1 27.2 27.2 27.8
420 30.5 28.0 20.2 24.9 22.3 30.0 24.9 26.5 26.2 30.0 28.2 28.2 29.0
440 31.6 29.0 22.0 25.8 23.0 31.0 26.0 28.0 26.0 30.6 29.2 29.8 30.7
460 33.0 30.0 23.8 26.9 23.6 32.0 27.2 29.5 25.0 31.0 30.0 30.9 32.0
470 (COM) 34.0 30.3 24.8 27.3 24.0 32.4 28.0 30.2 25.5 31.1 30.2 31.1 32.8
480 35.0 31.1 25.5 27.5 24.3 32.4 28.1 30.4 25.9 31.1 30.5 31.5 32.8
500 35.1 31.4 24.8 27.6 24.0 32.1 27.4 30.4 26.0 31.6 30.5 32.0 32.9
520 35.9 31.9 24.5 27.5 23.9 32.0 27.0 30.0 26.0 32.1 30.1 32.3 33.0
540 37.1 32.9 24.4 27.5 23.9 32.3 27.0 30.0 26.0 32.1 30.1 32.6 33.1
546 (COM) 37.5 33.1 24.3 27.5 23.9 32.2 26.9 30.0 26.0 32.1 30.3 32.8 33.1
560 38.1 33.8 24.1 27.3 24.0 32.1 26.8 30.0 25.9 32.3 30.7 32.9 33.1
580 39.0 34.2 24.0 27.1 23.5 32.0 26.3 30.0 25.7 32.5 31.0 33.0 33.8
589 (COM) 39.0 34.6 23.9 27.0 23.4 32.0 26.1 30.0 25.5 32.6 31.1 33.0 33.8
600 39.0 34.8 23.8 26.9 23.2 32.0 26.0 29.8 25.3 32.6 31.3 32.9 33.7
620 39.4 35.3 23.5 26.6 23.0 32.3 25.6 29.0 25.0 32.0 31.3 32.8 33.3
640 40.0 36.7 23.0 26.1 22.8 31.9 25.3 28.9 24.6 31.5 32.0 32.7 33.4
650 (COM) 40.3 37.0 22.9 25.8 22.7 31.6 25.1 28.9 24.2 31.5 32.1 32.5 33.3
660 40.8 37.6 22.8 25.3 22.4 31.2 25.0 28.8 24.2 31.5 32.4 32.3 33.1
680 41.8 38.3 22.5 25.7 22.2 30.8 24.9 28.3 24.1 31.7 32.9 32.2 33.3
700 42.2 39.2 22.2 26.0 22.0 31.0 24.7 27.9 24.0 31.4 33.0 32.0 33.8

Minerals 2023,13, 381 7 of 20
Table 2. Chemical composition of caswellsilverite (1) and “mineral X” (2), Figure 3b.
1 2 1 2
n = 9 s.d. range n = 1 apfu apfu
Si n.d. 0.64 S 2.00 2.00
S 46.37 0.24 45.81–46.69 37.58 Si 0.04
Ca 0.31 0.08 0.24–0.46 2.34 Ca 0.01 0.10
Zn n.d. 0.29 Zn 0.01
Fe 0.37 0.06 0.28–0.50 7.94 Fe3+ 0.01 0.24
Cr 36.65 0.36 35.89–37.13 30.18 Cr3+ 0.79 0.99
V 0.33 0.02 0.30–0.35 0.49 Cr4+ 0.18
Ti 0.13 0.07 0.08–0.30 n.d. V3+ 0.01 0.02
Al n.d. 0.14 Al 0.01
Na 12.70 0.52 11.82–13.75 0.60 Na 0.77 0.05
Sr 1.82 0.03 1.78–1.88 1.66 Sr 0.03 0.03
Ba n.d. 9.83 Ba 0.12
H2O 1.32 0–0.23 7.80
Total 100.00 100.00 H2O 0.10 0.74
n.d.: not detected
Minerals 2023, 13, x FOR PEER REVIEW 8 of 21
Figure 5. (a) The wall of the gaseous channel in gehlenite paralava is covered by sulphides (replaced by goethite) with
native iron inclusions; the fragments shown in the frames are magnified in Figure 5b,c. (b) Lamellar pyrrhotite with
parallel intergrowths of grokhovskyite. (c) Pseudomorph after pyrrhotite filled with iron hydroxides and sulphates
with pyrite impurity; the fragment in the frame is magnified in Figure 5d. (d) Pseudomorph after grokhovskyite (?)
(“mineral X”) and gmalimite relics on the boundary of goethite, pyrite and unidentified iron sulphate aggregate. BSE
images. Cws = caswellsilverite; Csp = cuspidine; Ett = ettringite; Fap = fluorapatite; Gh = gehlenite; Gma = gmalimite;
Gth = goethite; Ghy = grokovskyite; Fe = native iron; HSi = hydrosilcates; Prv = perovskite; Pwo = pseudowollastonite;
Py = pyrite; Pyh = pyrrhotite; Rnk = rankinite; Ss = unidentified chromium sulphates; Tch = tacharanite; X = “mineral
X”.
Figure 5.
(
a
) The wall of the gaseous channel in gehlenite paralava is covered by sulphides
(replaced by goethite) with native iron inclusions; the fragments shown in the frames are magnified in
Figure 5b,c. (
b
) Lamellar pyrrhotite with parallel intergrowths of grokhovskyite. (
c
) Pseudomorph
after pyrrhotite filled with iron hydroxides and sulphates with pyrite impurity; the fragment in
the frame is magnified in Figure 5d. (
d
) Pseudomorph after grokhovskyite (?) (“mineral X”)
and gmalimite relics on the boundary of goethite, pyrite and unidentified iron sulphate aggre-
gate. BSE images. Cws = caswellsilverite; Csp = cuspidine; Ett = ettringite; Fap = fluorapatite;
Gh = gehlenite; Gma = gmalimite; Gth = goethite; Ghy = grokovskyite; Fe = native iron; HSi = hydrosil-
cates; Prv = perovskite; Pwo = pseudowollastonite; Py = pyrite; Pyh = pyrrhotite; Rnk = rankinite;
Ss = unidentified chromium sulphates; Tch = tacharanite; X = “mineral X”.

Minerals 2023,13, 381 8 of 20
Minerals 2023, 13, x FOR PEER REVIEW 9 of 21
Figure 6. (a,b) Grokhovskyite exhibits high bireflectance (a—II to polarizer, b—⊥ to polarizer), frag-
ment magnified in Figure 6c is outlined by frame; reflected light. (c) BSE image (grokhovskyite is
shown by an arrow) and X-Ray maps of S, Fe, Cr, Cu, and Ba distribution. Pyh = pyrrhotite; Ghy =
grokhovskyite.
Table 3. Chemical composition of grokhovskyite (1), “mineral Х”(2,4) and pyrrhotite (3,5)..
Figure 5b Figure 5d
1 2 3 4 5
wt.% mean 7 s.d. range mean 3 mean 7 s.d. range mean 8 s.d. range mean 7 s.d. range
Si n.d. n.d. n.d. 0.19 0.04 0.14–0.28 n.d.
Al n.d. n.d. n.d. 0.07 0.01 0.06–0.09 n.d.
S 34.70 0.79 33.33–35.69 37.32 38.57 0.29 37.99–38.90 40.25 1.01 37.68–41.03 38.34 0.47 37.78–39.13
K n.d. 0.41 n.d. 0.29 0.05 0.23–0.38 n.d.
Ca 1.13 0.39 0.70–1.90 1.93 0.29 0.06 0.21–0.36 1.32 0.45 0.97–2.42 n.d.
Zn n.d. 0.12 n.d. 0.59 0.43 0.12–1.47 n.d.
Cu 28.91 0.95 27.49–30.02 1.97 n.d. 0.38 0.33 0.04–0.94 n.d.
Fe 4.41 2.38 2.52–9.96 17.03 57.35 0.31 56.67–57.56 11.62 1.06 9.99–12.96 57.38 0.58 56.34–58.10
Mn n.d. 0.15 0.14 0.09 0.05–0.32 0.78 0.30 0.40–1.21 0.33 0.11 0.18–0.48
Cr 26.51 0.53 25.61–27.09 25.97 1.51 0.25 1.23–2.02 30.88 0.71 29.15–31.75 2.15 0.25 1.74–2.42
V 0.20 0.01 0.18–0.23 0.33 1.00 0.17 0.80–1.30 0.22 0.05 0.15–0.32 1.07 0.11 0.98–1.29
Na 0.07 0.02 0.04–0.09 0.11 n.d. 0.17 0.06 0.10–0.29 n.d.
Sr 0.27 0.05 0.21–0.38 2.03 n.d. 1.24 0.14 1.06–1.54 n.d.
Ba 0.45 0.12 0.20–0.62 4.07 n.d. 6.53 0.68 5.79–7.70 n.d.
H2O 3.36 8.23 n.d. 5.45 n.d.
Total 100.00
100.00 98.87
100.00 99.28
apfu
Si 0.01 0.01
Al 0.01
S 2.00 2.00 1.00 2.00 1.00
K 0.02 0.01
Ca 0.05 0.08 0.01 0.05
Zn
0.01
Cu 0.84 0.05 0.01
Fe 0.15 0.52 0.85 0.33 0.86
Mn
0.02
Cr 0.94 0.86 0.02 0.95 0.03
V 0.01 0.01 0.02 0.01 0.02
Figure 6.
(
a
,
b
) Grokhovskyite exhibits high bireflectance (
a
—
k
to polarizer,
b
—
⊥
to polarizer),
fragment magnified in Figure 6c is outlined by frame; reflected light. (
c
) BSE image (grokhovskyite
is shown by an arrow) and X-Ray maps of S, Fe, Cr, Cu, and Ba distribution. Pyh = pyrrhotite;
Ghy = grokhovskyite.
Table 3. Chemical composition of grokhovskyite (1), “mineral X”(2,4) and pyrrhotite (3,5).
Figure 5b Figure 5d
1 2 3 4 5
wt.% mean 7 s.d. range mean 3 mean 7 s.d. range mean 8 s.d. range mean 7 s.d. range
Si n.d. n.d. n.d. 0.19 0.04 0.14–0.28 n.d.
Al n.d. n.d. n.d. 0.07 0.01 0.06–0.09 n.d.
S 34.70 0.79 33.33–35.69 37.32 38.57 0.29 37.99–38.90 40.25 1.01 37.68–41.03 38.34 0.47 37.78–39.13
K n.d. 0.41 n.d. 0.29 0.05 0.23–0.38 n.d.
Ca 1.13 0.39 0.70–1.90 1.93 0.29 0.06 0.21–0.36 1.32 0.45 0.97–2.42 n.d.
Zn n.d. 0.12 n.d. 0.59 0.43 0.12–1.47 n.d.
Cu 28.91 0.95 27.49–30.02 1.97 n.d. 0.38 0.33 0.04–0.94 n.d.
Fe 4.41 2.38 2.52–9.96 17.03 57.35 0.31 56.67–57.56 11.62 1.06 9.99–12.96 57.38 0.58 56.34–58.10
Mn n.d. 0.15 0.14 0.09 0.05–0.32 0.78 0.30 0.40–1.21 0.33 0.11 0.18–0.48
Cr 26.51 0.53 25.61–27.09 25.97 1.51 0.25 1.23–2.02 30.88 0.71 29.15–31.75 2.15 0.25 1.74–2.42
V 0.20 0.01 0.18–0.23 0.33 1.00 0.17 0.80–1.30 0.22 0.05 0.15–0.32 1.07 0.11 0.98–1.29
Na 0.07 0.02 0.04–0.09 0.11 n.d. 0.17 0.06 0.10–0.29 n.d.
Sr 0.27 0.05 0.21–0.38 2.03 n.d. 1.24 0.14 1.06–1.54 n.d.
Ba 0.45 0.12 0.20–0.62 4.07 n.d. 6.53 0.68 5.79–7.70 n.d.
H2O 3.36 8.23 n.d. 5.45 n.d.
Total 100.00 100.00 98.87 100.00 99.28
apfu
Si 0.01 0.01
Al 0.01
S 2.00 2.00 1.00 2.00 1.00
K 0.02 0.01
Ca 0.05 0.08 0.01 0.05
Zn 0.01
Cu 0.84 0.05 0.01
Fe 0.15 0.52 0.85 0.33 0.86
Mn 0.02
Cr 0.94 0.86 0.02 0.95 0.03
V 0.01 0.01 0.02 0.01 0.02
Na 0.01 0.01 0.01
Sr 0.01 0.04 0.02
Ba 0.01 0.05 0.08
H2O 0.35 0.79 0.48
n.d.–not detected.

Minerals 2023,13, 381 9 of 20
Minerals 2023, 13, x FOR PEER REVIEW 10 of 21
Na 0.01 0.01 0.01
Sr 0.01 0.04 0.02
Ba 0.01 0.05 0.08
H2O 0.35 0.79 0.48
n.d.–not detected.
Figure 7. Grokhovskyite forms a rim on an altered сaswellsilverite crystal (a, BSE; b, reflected light).
Cws = caswellsilverite; Gh = gehlenite; Ghy = grokhovskyite; Slh = schöllhornite; X = “mineral X”.
Figure 8. (a) Potentially new mineral AgCrS2 in gehlenite–pseudowollastonite paralava. The frag-
ment magnified in Figure 8b is outlined by the frame. (b,c) Crystal of AgCrS2: b, BSE; c, reflected
light. (d) Schreibersite–iron eutectic and pyrrhotite with daubréelite lamellas from an association
with AgCrS2. a, b, d—BSE; c, reflected light. Csp = cuspidine; Dbr = daubréelite; Ett = ettringite; Fap
= fluorapatite; Fe = native iron; Gh = gehlenite; Prv = perovskite; Pwo = pseudowollastonite; Pyh =
pyrrhotite; Scb = schreibersite.
Table 4. Chemical composition of Ag analogue of grokhovskyite.
wt.% n = 14 s.d. Range apfu
S 29.10 1.65 25.27–31.82 2.00
V 0.25 0.15 0–0.50 0.01
Cr 23.07 1.26 20.89–24.59 0.98
Fe 0.72 0.83 0–3.10 0.03
Ni 0.31 0.35 0–1.00 0.01
Cu 2.06 0.99 0–3.60 0.07
Ag 43.60 2.91 39.91–49.85 0.89
Total 99.11
Schöllhornite usually forms thin transition zones between caswellsilvertite and “min-
eral Х” (Figure 3d). More rarely, relatively large relics are preserved in the central part of
“mineral X” pseudomorphs (Figure 9). Because of the small size of schöllhornite, micro-
probe measurements were performed using an electron beam size of 1–2 μm, so during
Figure 7.
Grokhovskyite forms a rim on an altered caswellsilverite crystal ((
a
), BSE; (
b
), reflected light).
Cws = caswellsilverite; Gh = gehlenite; Ghy = grokhovskyite; Slh = schöllhornite; X = “mineral X”.
A potentially new mineral Ag analogue of grokhovskyite was found only once in
gehlenite paralava, where pseudowollastonite was widely distributed (Figure 8a–c). In
this paralava, especially on the boundary with the altered country rock, rounded ag-
gregates of schreibersite–iron eutectic are intergrown with pyrrhotite containing very
thin lamellas of daubréelite. In Figure 8d, the darker part of the aggregate has the
composition ~(Fe
0.57
Cr
0.24
V
0.06
)
Σ0.84
S, and the lighter part ~(Fe
0.64
Cr
0.20
V
0.07
)
Σ0.91
S. The
composition of the Ag analogue of grokhovskyite was obtained using SEM/EDS:
(Ag
+0.89
Cu
+0.07
)
Σ0.96
(Cr
3+0.98
Fe
3+0.03
V
3+0.01
Ni
0.01
)
Σ1.04
S
2
(Table 4). The measured reflectance
varies within the range of 23.5%–30.4% (Figure 4; Table 1), but the reflectance values were
probably lowered as the mineral is quickly altered in air.
Minerals 2023, 13, x FOR PEER REVIEW 10 of 21
Na 0.01 0.01 0.01
Sr 0.01 0.04 0.02
Ba 0.01 0.05 0.08
H2O 0.35 0.79 0.48
n.d.–not detected.
Figure 7. Grokhovskyite forms a rim on an altered сaswellsilverite crystal (a, BSE; b, reflected light).
Cws = caswellsilverite; Gh = gehlenite; Ghy = grokhovskyite; Slh = schöllhornite; X = “mineral X”.
Figure 8. (a) Potentially new mineral AgCrS2 in gehlenite–pseudowollastonite paralava. The frag-
ment magnified in Figure 8b is outlined by the frame. (b,c) Crystal of AgCrS2: b, BSE; c, reflected
light. (d) Schreibersite–iron eutectic and pyrrhotite with daubréelite lamellas from an association
with AgCrS2. a, b, d—BSE; c, reflected light. Csp = cuspidine; Dbr = daubréelite; Ett = ettringite; Fap
= fluorapatite; Fe = native iron; Gh = gehlenite; Prv = perovskite; Pwo = pseudowollastonite; Pyh =
pyrrhotite; Scb = schreibersite.
Table 4. Chemical composition of Ag analogue of grokhovskyite.
wt.% n = 14 s.d. Range apfu
S 29.10 1.65 25.27–31.82 2.00
V 0.25 0.15 0–0.50 0.01
Cr 23.07 1.26 20.89–24.59 0.98
Fe 0.72 0.83 0–3.10 0.03
Ni 0.31 0.35 0–1.00 0.01
Cu 2.06 0.99 0–3.60 0.07
Ag 43.60 2.91 39.91–49.85 0.89
Total 99.11
Schöllhornite usually forms thin transition zones between caswellsilvertite and “min-
eral Х” (Figure 3d). More rarely, relatively large relics are preserved in the central part of
“mineral X” pseudomorphs (Figure 9). Because of the small size of schöllhornite, micro-
probe measurements were performed using an electron beam size of 1–2 μm, so during
Figure 8.
(
a
) Potentially new mineral AgCrS
2
in gehlenite–pseudowollastonite paralava. The frag-
ment magnified in Figure 8b is outlined by the frame. (
b
,
c
) Crystal of AgCrS
2
: (
b
), BSE; (
c
), reflected
light. (
d
) Schreibersite–iron eutectic and pyrrhotite with daubréelite lamellas from an association
with AgCrS
2
. (
a
,
b
,
d
)—BSE; (
c
), reflected light. Csp = cuspidine; Dbr = daubréelite; Ett = ettringite;
Fap = fluorapatite; Fe = native iron; Gh = gehlenite; Prv = perovskite; Pwo = pseudowollastonite;
Pyh = pyrrhotite; Scb = schreibersite.

Minerals 2023,13, 381 10 of 20
Table 4. Chemical composition of Ag analogue of grokhovskyite.
wt.% n = 14 s.d. Range apfu
S 29.10 1.65 25.27–31.82 2.00
V 0.25 0.15 0–0.50 0.01
Cr 23.07 1.26 20.89–24.59 0.98
Fe 0.72 0.83 0–3.10 0.03
Ni 0.31 0.35 0–1.00 0.01
Cu 2.06 0.99 0–3.60 0.07
Ag 43.60 2.91 39.91–49.85 0.89
Total 99.11
Schöllhornite usually forms thin transition zones between caswellsilvertite and “min-
eral X” (Figure 3d). More rarely, relatively large relics are preserved in the central part of
“mineral X” pseudomorphs (Figure 9). Because of the small size of schöllhornite, micro-
probe measurements were performed using an electron beam size of 1–2
µ
m, so during the
measurements, some water and sodium were lost. Analytical data were obtained for three
grains (Table 5) as follows: {Na
0.09
Sr
0.03
Ca
0.01
}(Cr
3+0.98
Fe
3+0.01
V
3+0.01
)S
2·
0.55H
2
O (charge
3.17+/4
−
; Figure 9a); {Na
0.16
Sr
0.03
Ca
0.03
K
0.02
Ba
0.01
Sr
0.01
}(Cr
3+0.96
Fe
3+0.01
V
3+0.02
)S
2·
0.22H
2
O
(charge 3.31+/4
−
; Figure 9b); and {Na
0.27
Sr
0.03
Ca
0.03
Mn
2+0.01
}(Cr
3+0.98
Fe
3+0.02
V
3+0.02
)S
2·
0.30H
2
O
(charge 3.47+/4−; Figure 9c).
Minerals 2023, 13, x FOR PEER REVIEW 11 of 21
the measurements, some water and sodium were lost. Analytical data were obtained for
three grains (Table 5) as follows: {Na0.09Sr0.03Ca0.01}(Cr3+0.98Fe3+0.01V3+0.01)S2∙0.55H2O (charge
3.17+/4−; Figure 9a); {Na0.16Sr0.03Ca0.03K0.02Ba0.01Sr0.01}(Cr3+0.96Fe3+0.01V3+0.02)S2∙0.22H2O (charge
3.31+/4−; Figure 9b); and {Na0.27Sr0.03Ca0.03Mn2+0.01}(Cr3+0.98Fe3+0.02V3+0.02)S2∙0.30H2O (charge
3.47+/4−; Figure 9c).
Figure 9. (a–c) Schöllhornite relics in “mineral Х”; BSE. Csp = cuspidine; Fap = fluorapatite; Gh =
gehlenite; Hadr = “hydroandradite”; HSi = undiagnosed hydrosilicates; Pwo = pseudowollastonite;
Py = pyrite; Slh = schöllhornite; X = “mineral X”.
Table 5. Chemical composition of schöllhornite (1,3,5) and “mineral X”(2,4,6) from gehlenite para-
lava.
Figure 9a Figure 9b Figure 9c
1 2 3 4 5 6
wt.% n = 2 n = 6 s.d. range n = 5 s.d. range n = 3 n =1 n = 6 s.d. range
Si 0.07 0.28 0.07 0.18–0.37 0.13 0.06 0.06–0.22 0.13 0.42 0.25 0.08 0.09–0.32
Al n.d. 0.10 0.03 0.07–0.13 n.d. n.d. n.d. 0.06 0.01 0.05–0.08
S 48.95 37.62 0.65 36.69–38.69 49.61 1.61 47.34–51.33 40.24 46.99 38.32 0.49 37.54–39.04
K n.d. 0.15 0.14 0.03–0.44 0.73 0.21 0.39–0.96 0.25 0.14 0.20 0.20 0.04–0.63
Ca 0.36 1.80 0.30 1.37–2.24 0.96 0.68 0.38–2.30 1.07 0.80 1.48 0.28 0.92–1.81
Fe 0.24 10.27 0.70 8.84–11.06 0.30 0.04 0.24–0.33 8.40 0.74 10.82 0.44 10.11–11.46
Mn n.d. 1.00 0.44 0.59–1.93 n.d. 1.07 0.48 0.42 0.14 0.26–0.66
Cr 39.05 30.16 0.54 29.28–30.99 38.78 1.03 37.20–39.76 31.02 37.45 30.32 0.30 29.87–30.75
V 0.31 0.35 0.09 0.26–0.50 0.79 0.15 0.59–0.97 1.16 0.62 0.65 0.19 0.42–1.01
Na 1.57 0.06 0.01 0.05–0.08 2.92 1.98 1.25–6.75 0.42 4.61 0.08 0.05 0.04–0.19
Sr 1.88 1.68 0.02 1.64–1.71 2.13 0.41 1.86–2.93 1.78 2.03 1.69 0.04 1.64–1.77
Ba n.d. 11.22 0.63 10.34–12.05 0.58 0.84 0.03–2.24 11.21 1.35 11.35 0.96 9.44–12.54
H2O 7.58 5.32
3.08 3.25 4.38 4.36
Total 100.00 100.00
100.00 100.00 100.00 100.00
Si apfu 0.02
0.01 0.01 0.02 0.02
Al 0.01
S 2.00 2.00
2.00 2.00 2.00 2.00
K 0.01
0.02 0.01 0.01
Ca 0.01 0.08
0.03 0.04 0.03 0.06
Fe 0.01 0.31
0.01 0.24 0.02 0.32
Mn 0.03 0.03 0.01 0.01
Cr 0.98 0.99
0.96 0.95 0.98 0.98
V 0.01 0.01
0.02 0.04 0.02 0.02
Na 0.09 0.16 0.03 0.27 0.01
Sr 0.03 0.03 0.03 0.03 0.03 0.03
Ba 0.14 0.01 0.13 0.01 0.14
H2O 0.55 0.50 0.22 0.29 0.33 0.41
n.d.—not detected.
Figure 9.
(
a
–
c
) Schöllhornite relics in “mineral X”; BSE. Csp = cuspidine; Fap = fluorapatite;
Gh = gehlenite; Hadr = “hydroandradite”; HSi = undiagnosed hydrosilicates; Pwo = pseudowollas-
tonite; Py = pyrite; Slh = schöllhornite; X = “mineral X”.
“Mineral X” replacing schöllhornite has a relatively stable composition (Table 5):
{(Fe
3+0.31
Si
0.02
Al
0.01
)(Ba
0.14
Ca
0.08
Sr
0.03
Mn
2+0.03
K
0.01
}
Σ0.63
(Cr
3+0.99
V
3+0.01
)S
2·
0.5H
2
O (charge
4.61+/4
−
; Figure 9a); {(Fe
3+0.23
Si
0.01
)(Ba
0.13
Ca
0.04
Sr
0.03
Na
0.03
Mn
2+0.03
K
0.01
}
Σ0.63
(Cr
3+0.95
V
3+0.04
Fe
3+0.01
)S
2·
0.29H
2
O (charge 4.23+/4
−
; Figure 9b); and {(Fe
3+0.32
Si
0.02
)
(Ba
0.14
Ca
0.06
Sr
0.03
Mn
2+0.01
K
0.01
Na
0.01
}
Σ0.63
(Cr
3+0.98
V
3+0.02
)S
2·
0.41H
2
O (charge 4.54+/4
−
;
Figure 9c).
The composition of “mineral X” in association with pyrite (Fe
0.99
Ni
0.01
)S
2
and native
iron, respectively (Table 6), is as follows: {(Fe
3+0.33
Si
0.02
)(Ba
0.11
Ca
0.07
Sr
0.03
Mn
2+0.02
K
0.02
}
Σ0.60
(Cr
3+0.97
V
3+0.02
Fe
3+0.01
)S
2·
0.33H
2
O (charge 4.55+/4-; Figure 10a); and {(Fe
3+0.38
Si
0.01
)
(Ba
0.08
Ca
0.06
Sr
0.05
Na
0.02
Mn
2+0.01
K
0.01
}
Σ0.60
(Cr
3+0.99
V
3+0.01
)S
2·
0.40H
2
O (charge 4.61+/4
−
;
Figure 10b).

Minerals 2023,13, 381 11 of 20
Table 5.
Chemical composition of schöllhornite (1,3,5) and “mineral X”(2,4,6) from gehlenite paralava.
Figure 9a Figure 9b Figure 9c
1 2 3 4 5 6
wt.% n = 2 n = 6 s.d. range n = 5 s.d. range n = 3 n =1 n = 6 s.d. range
Si 0.07 0.28 0.07 0.18–0.37 0.13 0.06 0.06–0.22 0.13 0.42 0.25 0.08 0.09–0.32
Al n.d. 0.10 0.03 0.07–0.13 n.d. n.d. n.d. 0.06 0.01 0.05–0.08
S 48.95 37.62 0.65 36.69–38.69 49.61 1.61 47.34–51.33 40.24 46.99 38.32 0.49 37.54–39.04
K n.d. 0.15 0.14 0.03–0.44 0.73 0.21 0.39–0.96 0.25 0.14 0.20 0.20 0.04–0.63
Ca 0.36 1.80 0.30 1.37–2.24 0.96 0.68 0.38–2.30 1.07 0.80 1.48 0.28 0.92–1.81
Fe 0.24 10.27 0.70 8.84–11.06 0.30 0.04 0.24–0.33 8.40 0.74 10.82 0.44 10.11–11.46
Mn n.d. 1.00 0.44 0.59–1.93 n.d. 1.07 0.48 0.42 0.14 0.26–0.66
Cr 39.05 30.16 0.54 29.28–30.99 38.78 1.03 37.20–39.76 31.02 37.45 30.32 0.30 29.87–30.75
V 0.31 0.35 0.09 0.26–0.50 0.79 0.15 0.59–0.97 1.16 0.62 0.65 0.19 0.42–1.01
Na 1.57 0.06 0.01 0.05–0.08 2.92 1.98 1.25–6.75 0.42 4.61 0.08 0.05 0.04–0.19
Sr 1.88 1.68 0.02 1.64–1.71 2.13 0.41 1.86–2.93 1.78 2.03 1.69 0.04 1.64–1.77
Ba n.d. 11.22 0.63 10.34–12.05 0.58 0.84 0.03–2.24 11.21 1.35 11.35 0.96 9.44–12.54
H2O 7.58 5.32 3.08 3.25 4.38 4.36
Total
100.00 100.00
100.00
100.00
100.00
100.00
Si
apfu 0.02 0.01 0.01 0.02 0.02
Al 0.01
S 2.00 2.00 2.00 2.00 2.00 2.00
K 0.01 0.02 0.01 0.01
Ca 0.01 0.08 0.03 0.04 0.03 0.06
Fe 0.01 0.31 0.01 0.24 0.02 0.32
Mn 0.03 0.03 0.01 0.01
Cr 0.98 0.99 0.96 0.95 0.98 0.98
V 0.01 0.01 0.02 0.04 0.02 0.02
Na 0.09 0.16 0.03 0.27 0.01
Sr 0.03 0.03 0.03 0.03 0.03 0.03
Ba 0.14 0.01 0.13 0.01 0.14
H2O 0.55 0.50 0.22 0.29 0.33 0.41
n.d.—not detected.
Minerals 2023, 13, x FOR PEER REVIEW 12 of 21
“Mineral X” replacing schöllhornite has a relatively stable composition (Table 5):
{(Fe3+0.31Si0.02Al0.01)(Ba0.14Ca0.08Sr0.03Mn2+0.03K0.01}Σ0.63(Cr3+0.99V3+0.01)S2∙0.5H2O (charge 4.61+/4−;
Figure 9a); {(Fe3+0.23Si0.01)(Ba0.13Ca0.04Sr0.03Na0.03Mn2+0.03K0.01}Σ0.63(Cr3+0.95V3+0.04Fe3+0.01)S2∙0.29H2O
(charge 4.23+/4−; Figure 9b); and {(Fe3+0.32Si0.02)(Ba0.14Ca0.06Sr0.03Mn2+0.01K0.01Na0.01}Σ0.63(Cr3+0.98
V3+0.02)S2∙0.41H2O (charge 4.54+/4−; Figure 9c).
The composition of “mineral X” in association with pyrite (Fe0.99Ni0.01)S2 and native
iron, respectively (Table 6), is as follows: {(Fe3+0.33Si0.02)(Ba0.11Ca0.07Sr0.03Mn2+0.02K0.02}Σ0.60
(Cr3+0.97V3+0.02Fe3+0.01)S2∙0.33H2O (charge 4.55+/4-; Figure 10a); and
{(Fe3+0.38Si0.01)(Ba0.08Ca0.06Sr0.05Na0.02Mn2+0.01K0.01}Σ0.60(Cr3+0.99V3+0.01)S2∙0.40H2O (charge
4.61+/4−; Figure 10b).
“Mineral Х” is a potentially new mineral, which replaces caswellsilverite and
grokhovskyite, often forming full pseudomorphs (Figure 10c). The composition of its
main components varies considerably but has a constant ratio of Cr(±V,Fe)/S = 1:2: {Fe0.23–
0.38Ba0.08–0.14Ca0.04–0.10Sr0.02–0.05Na0–0.05Mn0–0.03}(Cr0.95–0.99V0.01–0.04Fe0–0.04)S2∙(H2O)0.29–0.74, with traces
of Al, Si, Cu, Zn, K (Tables 5 and 6). The mean crystal–chemical formula is
{Fe3+0.31Ba0.11Ca0.07Sr0.03Mn2+0.02Na0.02}(Cr3+0.97V3+0.02 Fe3+0.01)S2∙0.45H2O.
We failed to extract crystals of the studied minerals for a structural investigation;
therefore, to obtain information about their structural features, we used Raman spectros-
copy.
Figure 10. (a–c) Character of “mineral X” morphology; BSE images. Fe = native iron; Gh = gehlenite;
Pyh = pyrrhotite; Py = pyrite; Fap = fluorapatite; Hem = hematite; Tch = tacharanite; Rnk = rankinite;
Pwo = pseudowollastonite; X = “mineral X”.
Table 6. Chemical composition of “mineral Х” (1,4), pyrite (2,6), native iron (3), and pyrrhotite (5).
Figure 10a Figure 10b Figure 10c
1 2 3 4 5 6
wt.% mean 5 s.d. range mean 2 mean 4 mean 8 s.d. range mean 5 s.d. range mean 5 s.d. range
Si 0.29 0.10 0.17–0.42 n.d. n.d. 0.18 0.07 0.08–0.30 n.d. n.d.
Al 0.06 0.01 0.05–0.07 n.d. n.d. n.d. n.d. n.d. n.d.
S 38.97 0.47 38.29–39.53 53.15 n.d. 39.18 0.34 38.79–39.79 38.98 0.12 38.86–39.20 53.28 0.31 52.71–53.62
K 0.58 0.14 0.42–0.85 n.d. n.d. 0.24 0.12 0.06–0.49 n.d. n.d.
Ca 1.66 0.22 1.38–1.92 0.27 n.d. 1.57 0.38 1.08–2.29 n.d. n.d.
Cu n.d. 0.19 n.d. n.d. n.d. n.d. 0.16 0.03 0.13–0.22
Ni n.d. 0.33 1.63 n.d. n.d. n.d. 0.14 0.04 0.09–0.21
Co n.d. n.d. 0.27 n.d. n.d. n.d. n.d.
Fe 11.67 0.41 11.16–12.33 46.53 98.05 12.94 0.67 12.09–14.26 57.58 0.24 57.26–57.92 46.84 0.19 46.52–47.12
Mn 0.66 0.33 0.41–1.26 n.d. n.d. 0.39 0.20 0.11–0.78 0.41 0.12 0.28–0.57 n.d.
Cr 30.68 0.73 29.67–31.75 n.d. 0.10 31.32 0.35 30.75–31.84 1.84 0.20 1.61–2.09 0.10 0.14 0.02–0.37
V 0.77 0.29 0.32–1.12 n.d. n.d. 0.26 0.06 0.19–0.37 1.21 0.11 1.08–1.35 n.d.
Na 0.05 0.03 0.03–0.11 n.d. n.d. 0.23 0.20 0.06–0.63 n.d. n.d.
Sr 1.65 0.04 1.62–1.71 n.d. n.d. 2.77 0.55 2.08–3.79 n.d. n.d.
Ba 9.35 0.60 8.51–10.05 n.d. n.d. 6.51 1.82 3.40–8.90 n.d. n.d.
H2O 3.61 4.42
Total 100.00 100.46 100.05 100.00
100.02
100.52
Si apfu 0.02 0.01
S 2.00 2.00 2.00 1.00 2.00
K 0.02 0.01
Ca 0.07 0.01 0.06
Ni 0.01 0.02
Fe 0.34 1.00 0.98 0.38
0.85 1.01
Figure 10.
(
a
–
c
) Character of “mineral X” morphology; BSE images. Fe = native iron; Gh = gehlenite;
Pyh = pyrrhotite; Py = pyrite; Fap = fluorapatite; Hem = hematite; Tch = tacharanite; Rnk = rankinite;
Pwo = pseudowollastonite; X = “mineral X”.
“Mineral X” is a potentially new mineral, which replaces caswellsilverite and
grokhovskyite, often forming full pseudomorphs (Figure 10c). The composition of its
main components varies considerably but has a constant ratio of Cr(
±
V, Fe)/S = 1:2:
{Fe
0.23–0.38
Ba
0.08–0.14
Ca
0.04–0.10
Sr
0.02–0.05
Na
0–0.05
Mn
0–0.03
}(Cr
0.95–0.99
V
0.01–0.04
Fe
0–0.04
)S
2·
(H
2
O)
0.29–0.74
, with traces of Al, Si, Cu, Zn, K (Tables 5and 6). The mean crystal–chemical formula
is {Fe3+0.31 Ba0.11Ca0.07 Sr0.03Mn2+0.02 Na0.02}(Cr3+0.97 V3+0.02 Fe3+ 0.01)S2·0.45H2O.
We failed to extract crystals of the studied minerals for a structural investigation; there-
fore, to obtain information about their structural features, we used Raman spectroscopy.

Minerals 2023,13, 381 12 of 20
Table 6. Chemical composition of “mineral X” (1,4), pyrite (2,6), native iron (3), and pyrrhotite (5).
Figure 10a Figure 10b Figure 10c
1 2 3 4 5 6
wt.% mean 5 s.d. range mean 2 mean 4 mean 8 s.d. range mean 5 s.d. range mean 5 s.d. range
Si 0.29 0.10 0.17–0.42 n.d. n.d. 0.18 0.07 0.08–0.30 n.d. n.d.
Al 0.06 0.01 0.05–0.07 n.d. n.d. n.d. n.d. n.d. n.d.
S 38.97 0.47 38.29–39.53 53.15 n.d. 39.18 0.34 38.79–39.79 38.98 0.12 38.86–39.20 53.28 0.31 52.71–53.62
K 0.58 0.14 0.42–0.85 n.d. n.d. 0.24 0.12 0.06–0.49 n.d. n.d.
Ca 1.66 0.22 1.38–1.92 0.27 n.d. 1.57 0.38 1.08–2.29 n.d. n.d.
Cu n.d. 0.19 n.d. n.d. n.d. n.d. 0.16 0.03 0.13–0.22
Ni n.d. 0.33 1.63 n.d. n.d. n.d. 0.14 0.04 0.09–0.21
Co n.d. n.d. 0.27 n.d. n.d. n.d. n.d.
Fe 11.67 0.41 11.16–12.33 46.53 98.05 12.94 0.67 12.09–14.26 57.58 0.24 57.26–57.92 46.84 0.19 46.52–47.12
Mn 0.66 0.33 0.41–1.26 n.d. n.d. 0.39 0.20 0.11–0.78 0.41 0.12 0.28–0.57 n.d.
Cr 30.68 0.73 29.67–31.75 n.d. 0.10 31.32 0.35 30.75–31.84 1.84 0.20 1.61–2.09 0.10 0.14 0.02–0.37
V 0.77 0.29 0.32–1.12 n.d. n.d. 0.26 0.06 0.19–0.37 1.21 0.11 1.08–1.35 n.d.
Na 0.05 0.03 0.03–0.11 n.d. n.d. 0.23 0.20 0.06–0.63 n.d. n.d.
Sr 1.65 0.04 1.62–1.71 n.d. n.d. 2.77 0.55 2.08–3.79 n.d. n.d.
Ba 9.35 0.60 8.51–10.05 n.d. n.d. 6.51 1.82 3.40–8.90 n.d. n.d.
H2O 3.61 4.42
Total 100.00 100.46 100.05 100.00 100.02 100.52
Si
apfu 0.02 0.01
S 2.00 2.00 2.00 1.00 2.00
K 0.02 0.01
Ca 0.07 0.01 0.06
Ni 0.01 0.02
Fe 0.34 1.00 0.98 0.38 0.85 1.01
Mn 0.02 0.01 0.01
Cr 0.97 0.99 0.03
V 0.02 0.01 0.02
Na 0.02
Sr 0.03 0.05
Ba 0.11 0.08
H2O 0.33 0.40
n.d.—not detected.
5. Raman Investigation of Layered Chromium Disulphides
In the Raman spectra of caswellsilverite, there are two strong bands from Cr-S
vibrations typical for the spectra of synthetic NaCrS
2
: 316 (A
1
) and 252 cm
−1
(E
g
) [
25
]. An
orientation effect is observed: the band at 316 cm
−1
polarizes, and its intensity drops by a
factor of three times at polarization of the laser beam perpendicular to the direction of the
flattening crystal (Figure 11a,b). To avoid artefacts in the spectra of the studied minerals,
we also obtained their spectra after the laser-induced heating in air. The Raman spectrum
of thermally changed caswellsilverite is related to sodium chromate. The strongest band in
the spectrum at about 850 cm
−1
is related to A
1
vibrations in (CrO
4
)
2-
[
26
–
29
] (Figure 11c).
The Raman spectra of grokhovskyite were measured on lamellar crystal in two
orientations (Figure 12). The spectra featured weak bands at 315/319 cm
−1
(A
1
) and
253/251 cm−1(Eg), which are typical for synthetic CuCrS2[30,31].
The bands in the Raman spectrum of the potentially new mineral AgCrS
2
(Figure 13)
had a weak intensity that can be explained by its surface quality due to high instability in
the ambient conditions (Figure 8c). There are also bands in the spectrum related to Cr-S
vibration: 644, 320 (A1), 279(?) и250 (Eg) cm−1[25,32–34].
We measured the Raman spectra of schöllhornite and “mineral X” and their products
as a result of thermal change under the laser beam (Figure 14). It should be emphasised
that in no case did we observe active vibrational modes from OH/H2O.

Minerals 2023,13, 381 13 of 20
Minerals 2023, 13, x FOR PEER REVIEW 13 of 21
Mn 0.02 0.01
0.01
Cr 0.97 0.99
0.03
V 0.02 0.01 0.02
Na 0.02
Sr 0.03 0.05
Ba 0.11 0.08
H2O 0.33 0.40
n.d.—not detected.
5. Raman Investigation of Layered Chromium Disulphides
In the Raman spectra of caswellsilverite, there are two strong bands from Cr-S vibra-
tions typical for the spectra of synthetic NaCrS2: 316 (A1) and 252 сm−1 (Eg) [25]. An orien-
tation effect is observed: the band at 316 cm−1 polarizes, and its intensity drops by a factor
of three times at polarization of the laser beam perpendicular to the direction of the flat-
tening crystal (Figure 11a,b). To avoid artefacts in the spectra of the studied minerals, we
also obtained their spectra after the laser-induced heating in air. The Raman spectrum of
thermally changed caswellsilverite is related to sodium chromate. The strongest band in
the spectrum at about 850 cm−1 is related to A1 vibrations in (CrO4)2- [26–29] (Figure 11c).
Figure 11. (a,b) Raman spectra of caswellsilverite in two orientations: perpendicular (a) and parallel
(b) to the polarized incident laser beam. Spots of Raman spectra measurement are shown by white
circles in reflected light images. (c) Raman spectrum obtained after thermal laser effect.
The Raman spectra of grokhovskyite were measured on lamellar crystal in two ori-
entations (Figure 12). The spectra featured weak bands at 315/319 cm−1 (A1) and 253/251
cm−1 (Eg), which are typical for synthetic CuCrS2 [30,31].
Figure 11.
(
a
,
b
) Raman spectra of caswellsilverite in two orientations: perpendicular (
a
) and parallel
(b) to the polarized incident laser beam. Spots of Raman spectra measurement are shown by white
circles in reflected light images. (c) Raman spectrum obtained after thermal laser effect.
Minerals 2023, 13, x FOR PEER REVIEW 14 of 21
Figure 12. Raman spectra of grokhovskyite in two orientations: perpendicular (a) and parallel (b) to
the polarized incident laser beam Points of spectra measurements are marked by white circles in
reflected light images.
The bands in the Raman spectrum of the potentially new mineral AgCrS2 (Figure 13)
had a weak intensity that can be explained by its surface quality due to high instability in
the ambient conditions (Figure 8c). There are also bands in the spectrum related to Cr-S
vibration: 644, 320 (A1), 279(?) и 250 (Eg) cm−1 [25,32–34].
Figure 13. Raman spectrum of potentially new mineral AgCrS2.
We measured the Raman spectra of schöllhornite and “mineral Х” and their products
as a result of thermal change under the laser beam (Figure 14). It should be emphasised
that in no case did we observe active vibrational modes from OH/Н2О.
In the schöllhornite spectrum (Figure 14c), there were two strong bands at 336 and
276 cm−1 related to vibrations A1 and Eg in the (CrS2)- layers, and there was a strong band
near 467 cm−1, which may correspond to the S-S bond [34]. An effect of the dimerization
of sulphur was noted in NaCr2/3Ti1/3S2 disulphide as a result of the migration of Cr to the
Na-vacancies [35]. It is interesting that schöllhornite, thermally affected by the Raman mi-
croscope laser beam, was replaced by escolaite, Cr2O3 (Figure 14e).
Non-oriented Raman spectra for “mineral X” were obtained for its full pseudomorph
after disulphide, probably grokhovskyite (Figure 14a), with the empirical formula
{Fe3+0.30Ba0.08Ca0.06Sr0.02Si0.02Mn2+0.02Cu0.01Zn0.01Al0.01Na0.01}(Cr0.95Fe3+0.04V3+0.01)S2∙0.53H2O (Ta-
ble 3), and for a rim around schöllhornite (Figures 9a and 14d) with the composition
{Fe3+0.31Ba0.14Ca0.08Sr0.03Mn2+0.03Si0.02Al0.01K0.01}(Cr0.99V3+0.01)S2∙0.50H2O (Table 5). These compo-
sitions are similar and can be described by the simplified formula ∼ {Fe0.3R2+0.2–0.3}CrS2∙
0.5H2O, R2+=Ba,Sr,Ca. Nevertheless, their spectra differ significantly. These differences can
be related both to the orientation effect and to features of the occupation of space between
the (CrS2)1- layers and changes in the Cr valence state. The Raman spectrum of the full
Figure 12.
Raman spectra of grokhovskyite in two orientations: perpendicular (
a
) and parallel (
b
)
to the polarized incident laser beam Points of spectra measurements are marked by white circles in
reflected light images.

Minerals 2023,13, 381 14 of 20
Minerals 2023, 13, x FOR PEER REVIEW 14 of 21
Figure 12. Raman spectra of grokhovskyite in two orientations: perpendicular (a) and parallel (b) to
the polarized incident laser beam Points of spectra measurements are marked by white circles in
reflected light images.
The bands in the Raman spectrum of the potentially new mineral AgCrS2 (Figure 13)
had a weak intensity that can be explained by its surface quality due to high instability in
the ambient conditions (Figure 8c). There are also bands in the spectrum related to Cr-S
vibration: 644, 320 (A1), 279(?) и 250 (Eg) cm−1 [25,32–34].
Figure 13. Raman spectrum of potentially new mineral AgCrS2.
We measured the Raman spectra of schöllhornite and “mineral Х” and their products
as a result of thermal change under the laser beam (Figure 14). It should be emphasised
that in no case did we observe active vibrational modes from OH/Н2О.
In the schöllhornite spectrum (Figure 14c), there were two strong bands at 336 and
276 cm−1 related to vibrations A1 and Eg in the (CrS2)- layers, and there was a strong band
near 467 cm−1, which may correspond to the S-S bond [34]. An effect of the dimerization
of sulphur was noted in NaCr2/3Ti1/3S2 disulphide as a result of the migration of Cr to the
Na-vacancies [35]. It is interesting that schöllhornite, thermally affected by the Raman mi-
croscope laser beam, was replaced by escolaite, Cr2O3 (Figure 14e).
Non-oriented Raman spectra for “mineral X” were obtained for its full pseudomorph
after disulphide, probably grokhovskyite (Figure 14a), with the empirical formula
{Fe3+0.30Ba0.08Ca0.06Sr0.02Si0.02Mn2+0.02Cu0.01Zn0.01Al0.01Na0.01}(Cr0.95Fe3+0.04V3+0.01)S2∙0.53H2O (Ta-
ble 3), and for a rim around schöllhornite (Figures 9a and 14d) with the composition
{Fe3+0.31Ba0.14Ca0.08Sr0.03Mn2+0.03Si0.02Al0.01K0.01}(Cr0.99V3+0.01)S2∙0.50H2O (Table 5). These compo-
sitions are similar and can be described by the simplified formula ∼ {Fe0.3R2+0.2–0.3}CrS2∙
0.5H2O, R2+=Ba,Sr,Ca. Nevertheless, their spectra differ significantly. These differences can
be related both to the orientation effect and to features of the occupation of space between
the (CrS2)1- layers and changes in the Cr valence state. The Raman spectrum of the full
Figure 13. Raman spectrum of potentially new mineral AgCrS2.
Minerals 2023, 13, x FOR PEER REVIEW 15 of 21
pseudomorph of “mineral X” after caswellsilverite (?) resembles that of schöllhornite (Fig-
ure 14a,c). It contains the bands (cm−1): 459, 409, 353, 288, 246, 158 and 102. Band 459 cm−1
is related to S-S vibrations [34]. On the spectrum of the phase from the rim, there is a series
of bands in the range 250–350 cm−1, corresponding to Cr-S vibrations in the disulphide
layers (cm−1): 254, 275, 290, 313, 321, 333, 344. It is notable that after laser heating, the spec-
tra of caswellsilverite and “mineral X” visually differed (Figure 14b,f). However, in both
spectra, three main vibrational modes related to the three new-formed phases can be dis-
tinguished: near 855 cm−1: (CrO4)2-, chromate; 680–700 cm−1, phase of the ACrO3-type; and
540–550 cm−1: (Cr2O3) [36–38].
Figure 14. Raman spectra of caswellsilverite replacement products: (a,b,d,f)—“mineral X” ((a,d):
original; (b,f): thermally effected); (c,e): schöllhornite ((c), original; (e), after thermal effect).
The Raman investigation of the natural chromium disulphides NaCrS2, AgCrS2, and
CuCrS2 confirmed their identity with the synthetic analogues (Figures 11–13).
Figure 14.
Raman spectra of caswellsilverite replacement products: (
a
,
b
,
d
,
f
)—“mineral X”
((a,d): original; (b,f): thermally effected); (c,e): schöllhornite ((c), original; (e), after thermal effect).

Minerals 2023,13, 381 15 of 20
In the schöllhornite spectrum (Figure 14c), there were two strong bands at 336 and
276 cm
−1
related to vibrations A
1
and E
g
in the (CrS
2
)
−
layers, and there was a strong band
near 467 cm
−1
, which may correspond to the S-S bond [
34
]. An effect of the dimerization
of sulphur was noted in NaCr
2/3
Ti
1/3
S
2
disulphide as a result of the migration of Cr to
the Na-vacancies [
35
]. It is interesting that schöllhornite, thermally affected by the Raman
microscope laser beam, was replaced by escolaite, Cr2O3(Figure 14e).
Non-oriented Raman spectra for “mineral X” were obtained for its full pseudo-
morph after disulphide, probably grokhovskyite (Figure 14a), with the empirical for-
mula {Fe
3+0.30
Ba
0.08
Ca
0.06
Sr
0.02
Si
0.02
Mn
2+0.02
Cu
0.01
Zn
0.01
Al
0.01
Na
0.01
}(Cr
0.95
Fe
3+0.04
V
3+0.01
)
S
2·
0.53H
2
O (Table 3), and for a rim around schöllhornite (Figures 9a and 14d) with the
composition {Fe
3+0.31
Ba
0.14
Ca
0.08
Sr
0.03
Mn
2+0.03
Si
0.02
Al
0.01
K
0.01
}(Cr
0.99
V
3+0.01
)S
2·
0.50H
2
O
(Table 5). These compositions are similar and can be described by the simplified for-
mula ~ {Fe
0.3
R
2+0.2–0.3
}CrS
2·
0.5H
2
O, R
2+
= Ba, Sr, Ca. Nevertheless, their spectra differ
significantly. These differences can be related both to the orientation effect and to features
of the occupation of space between the (CrS
2
)
1−
layers and changes in the Cr valence state.
The Raman spectrum of the full pseudomorph of “mineral X” after caswellsilverite (?)
resembles that of schöllhornite (Figure 14a,c). It contains the bands (cm
−1
): 459, 409, 353,
288, 246, 158 and 102. Band 459 cm
−1
is related to S-S vibrations [
34
]. On the spectrum of
the phase from the rim, there is a series of bands in the range 250–350 cm
−1
, corresponding
to Cr-S vibrations in the disulphide layers (cm
−1
): 254, 275, 290, 313, 321, 333, 344. It is
notable that after laser heating, the spectra of caswellsilverite and “mineral X” visually
differed (Figure 14b,f). However, in both spectra, three main vibrational modes related
to the three new-formed phases can be distinguished: near 855 cm
−1
: (CrO
4
)
2-
, chromate;
680–700 cm−1, phase of the ACrO3-type; and 540–550 cm−1: (Cr2O3) [36–38].
The Raman investigation of the natural chromium disulphides NaCrS
2
, AgCrS
2
, and
CuCrS2confirmed their identity with the synthetic analogues (Figures 11–13).
6. Genesis and Alteration of Chromium Disulphides in Pyrometamorphic Rock
Highly reducing conditions in the terrestrial pyrometamorphic combustion process is
a rare phenomenon that leads to the appearance of minerals typical for meteorites [
1
,
18
,
39
].
“Meteoritic” minerals, mainly phosphides, form at the contact facies of black, reduced
pyrrhotite-bearing Hatrurim Complex paralavas intruded into the country rocks containing
carbonaceous matter, which play the role of reductant [
1
,
18
]. It should be emphasised that
yellow-green, brown oxidized paralavas with a mineral composition close to that of black
paralava are widespread in the Hatrurim Complex, especially in the Hatrurim Basin, and
contain mainly Fe3+-bearing minerals [19].
Combustion processes during pyrometamorphism of a large area, as in the case of
the Hatrurim Complex, determine the formation of a significant volume of reducing gases
(CH
4
, H
2
, H
2
S, CO, NO) as a result of the pyrolytic decomposition of organic matter
(bitumen, oil) contained in the sedimentary protolith. The crystallization of highly re-
duced phases proceeds along the paths of flow of reducing gases. For example, small
crystals of oldhamite, CaS, formed on the walls of micron-sized channels penetrating
spurrite marble of the Hatrurim Basin [
40
]. Sometimes reducing gases have a significant
effect on pyrometamorphic rocks, which is expressed in the crystallization of rock-forming
oldhamite in larnite rock (Figure 15a) by the reaction: CaO + H
2
S
gas
= CaS + H
2
O
gas
.
In larnite rock, oldhamite is associated with Fe
3+
-bearing minerals such as brownmil-
lerite, Ca
2
FeAlO
5
(Figure 15a), and cannot be an indicator of the reduction conditions for
the entire rock volume.

Minerals 2023,13, 381 16 of 20
Minerals 2023, 13, x FOR PEER REVIEW 17 of 21
Figure 15. (a) Oldhamite-bearing fluormayenite–larnite rock from the Hatrurim Basin (Har Parsa
Mt.). (b) Inclusion of oldhamite in pseudowollastonite from phosphide-bearing breccia. Bmlr =
brownmillerite; Cal = calcite; Fmy = fluormayenite; Hgr = hydrogrossulare; Lar = larnite; Old = old-
hamite; Pwo = pseudowollastonite.
Caswellsilverite crystallizes in the central porous parts of paralava together with pyr-
rhotite (Figure 2b), whereas in non-porous fragments of paralava, small iron drops form
(Figure 2a) that can indicate that the primary iron melt is enriched in sulphur carried by
combustion gases. Experimental studies indicate that caswellsilverite (and grokhovskyite)
form in paralava at relatively higher oxygen activity 0 ≤ ΔIW< −2 in comparison with old-
hamite [42]. This suggests that super- or high-reduction conditions (ΔIW ≈ −6–−2) at the
contact zone of paralava with clasts of altered country rock change within a distance of a
few centimetres (the central parts of paralava zones) to the reduction conditions near the
Fe/FeO (ΔIW ≈ 0) buffer. Caswellsilverite and pyrrhotite crystallize from sulphide melt
mosaically distributed in paralava between previously crystallized silicates (Figure 2b,c).
Sodium, which is necessary for сaswellsilverite genesis, is probably introduced into the
sa me por tion of the sulphide m elt as a result of the repl acement of flami te, Ca2-x (Na,K)x(Si1-
xPx)O4 by rankinite, Ca3Si2O7 [18]. In experiments, NaCrS2 crystals were obtained from al-
kaline polysulfide melt at temperatures below 1000 °C. It was also shown that they de-
compose slowly in the atmosphere at room temperature and are relatively quickly oxi-
dized at temperatures above 1000 °C with the formation of NaCrO2 and Cr2O3 crystals
[43]. Both types of caswellsilverite high-temperature alteration products we observed to
form due to the thermal effect of the Raman probe (Figures 11 and 14).
In a previous analysis of the conditions of the genesis of Cr-V-bearing phosphides
(barringerite, allabogdanite, andreyivanovite) in the same breccia, it was suggested that
high-reduction conditions are necessary for the enrichment of Fe(+P) melt by Cr and V [1].
Additionally, we noted a local enrichment of Fe(±P,C) melt by Cu (Figure 1d). All these
observations can be applied to sulphide melts, the crystallization of which between pre-
viously formed gehlenite crystals (Figure 2b,c), on solidified Fe drops (Figure 10b) and
wall cavities (Figure 5a) led to the formation of Fe-monosulfide with a higher Cr(+Cu)
concentration. Later, monosulphide transformed into lamellar polysynthetic aggregates
of pyrrhotite with the grokhovskyite exsolution structures (Figure 5b). The local enrich-
ment of sulphide melt by Ag led to the crystallization of a potentially new mineral AgCrS2
(Figure 8).
Hexagonal octahedral layers (CrS2)1-, between which M-sites of the monovalent cati-
ons Ag, Cu, and Na set, are present in the structures of layered chromium disulphides,
МCrS2 (Figure 16), [44–48]. The sodium is at the octahedral coordination, whereas Cu and
Ag are in the deformed tetrahedra. There are two types of tetrahedral site: α- and β- (Fig-
ure 16b) [45–49]. Ordered disulphide forms at temperatures below ∼500 °С as a result of
the occupation of the first type of site. In CuCrS2, an effect of some Cr moving into the
space between disulphide layers was observed [45] (Figure 16c).
Figure 15.
(
a
) Oldhamite-bearing fluormayenite–larnite rock from the Hatrurim Basin
(Har Parsa Mt.). (
b
) Inclusion of oldhamite in pseudowollastonite from phosphide-bearing breccia.
Bmlr = brownmillerite; Cal = calcite; Fmy = fluormayenite; Hgr = hydrogrossulare; Lar = larnite;
Old = oldhamite; Pwo = pseudowollastonite.
In considering the super- and high-reduced mineral associations in pyrometamorphic
rocks, two main forms of “meteorite” mineral formation should be taken into account:
(1) mineral formation reactions following the short-distance transport of reacting compo-
nents on the contact of hot paralava and country rock containing the reductant (carbona-
ceous matter); (2) mineral formation as a result of reducing gases reacting with minerals of
the early “clinker” association.
The generation of gehlenite paralava with “meteoritic” chromium disulphides took
place at the combustion foci at a high temperature (probably higher than 1500
◦
C) and
low pressure [
1
]. An intrusion of paralava into brecciated clay-carbonate sedimentary rock
containing phosphatised and graphitized organic matter as well as iron oxides caused
the formation of mineral aggregates of the Fe-P(+C, Cr, V) system on the boundary of
paralava and country rock (Figure 1a–c) as a result of high-temperature carbothermal
reduction reactions [
1
,
18
]. On iron phosphide aggregates presented by barringerite, and
schreibersite, the rim of the Fe-schreibersite eutectic was formed. This is where the mono-
sulphide phase, which later transforms into lamellar pyrrhotite and daubréelite aggregates
(Figures 1f and 8d), was detected. In rare cases, phosphides and pyrrhotite associate with
osbornite, TiN—a mineral-indicator of the super-reducing conditions (fO
2
< iron-wüstite
buffer ∆IW ≈ −6) [18,41].
In the studied phosphide-bearing breccia, a “meteoritic” sulphide, oldhamite, CaS,
rarely encountered as small rounded inclusions in pseudowollastonite from the paralava
contact zone, crystallizes from melt (Figure 15b), and can be an indicator of the reduc-
ing conditions. The investigation of sulphide genesis in “mercurian melt” showed that
oldhamite is stable at about ∆IW ≈ −2 [42].
Caswellsilverite crystallizes in the central porous parts of paralava together with
pyrrhotite (Figure 2b), whereas in non-porous fragments of paralava, small iron drops form
(Figure 2a) that can indicate that the primary iron melt is enriched in sulphur carried by
combustion gases. Experimental studies indicate that caswellsilverite (and grokhovskyite)
form in paralava at relatively higher oxygen activity 0
≤∆
IW<
−
2 in comparison with
oldhamite [
42
]. This suggests that super- or high-reduction conditions (
∆
IW
≈ −
6–
−
2)
at the contact zone of paralava with clasts of altered country rock change within a dis-
tance of a few centimetres (the central parts of paralava zones) to the reduction conditions
near the Fe/FeO (
∆
IW
≈
0) buffer. Caswellsilverite and pyrrhotite crystallize from sul-
phide melt mosaically distributed in paralava between previously crystallized silicates
(Figure 2b,c). Sodium, which is necessary for caswellsilverite genesis, is probably intro-
duced into the same portion of the sulphide melt as a result of the replacement of flamite,
Ca
2-x
(Na,K)
x
(Si
1-x
P
x
)O
4
by rankinite, Ca
3
Si
2
O
7
[
18
]. In experiments, NaCrS
2
crystals
were obtained from alkaline polysulfide melt at temperatures below 1000
◦
C. It was also
shown that they decompose slowly in the atmosphere at room temperature and are rela-
tively quickly oxidized at temperatures above 1000
◦
C with the formation of NaCrO
2
and

Minerals 2023,13, 381 17 of 20
Cr
2
O
3
crystals [
43
]. Both types of caswellsilverite high-temperature alteration products we
observed to form due to the thermal effect of the Raman probe (Figures 11 and 14).
In a previous analysis of the conditions of the genesis of Cr-V-bearing phosphides
(barringerite, allabogdanite, andreyivanovite) in the same breccia, it was suggested that
high-reduction conditions are necessary for the enrichment of Fe(+P) melt by Cr and
V [
1
]. Additionally, we noted a local enrichment of Fe(
±
P, C) melt by Cu (Figure 1d). All
these observations can be applied to sulphide melts, the crystallization of which between
previously formed gehlenite crystals (Figure 2b,c), on solidified Fe drops (Figure 10b) and
wall cavities (Figure 5a) led to the formation of Fe-monosulfide with a higher Cr(+Cu)
concentration. Later, monosulphide transformed into lamellar polysynthetic aggregates of
pyrrhotite with the grokhovskyite exsolution structures (Figure 5b). The local enrichment
of sulphide melt by Ag led to the crystallization of a potentially new mineral AgCrS
2
(Figure 8).
Hexagonal octahedral layers (CrS
2
)
1−
, between which M-sites of the monovalent
cations Ag, Cu, and Na set, are present in the structures of layered chromium disulphides,
MCrS
2
(Figure 16), [
44
–
48
]. The sodium is at the octahedral coordination, whereas Cu
and Ag are in the deformed tetrahedra. There are two types of tetrahedral site:
α
- and
β
-
(Figure 16b) [
45
–
49
]. Ordered disulphide forms at temperatures below ~500
◦
C as a result
of the occupation of the first type of site. In CuCrS
2
, an effect of some Cr moving into the
space between disulphide layers was observed [45] (Figure 16c).
Minerals 2023, 13, x FOR PEER REVIEW 18 of 21
Figure 16. Structures of trigonal synthetic layered chromium disulphides, projection on (010): (a)
Caswellsilverite analogue [44]; (b) analogue of potentially new mineral AgCrS2 [44], chromium oc-
cupies tetrahedral sites of the β-type, empty circles show vacancy sites of the α-type; (c) analogue
of grokhovskyite with vacancies in Cr-disulphide layer, fully occupied Cu-tetrahedral sites and ad-
ditional Cr-sites (deformed octahedron, green balls) in cation layer [45]. Atoms/polyhedra are
shown in green for Cr; dark blue for Cu; light blue for Ag; light yellow for Na; and yellow for S.
Low-temperature alterations of layered chromium disulphides are exclusively re-
flected in changes to the composition and structure of the monovalent cation layer,
whereas the hexagonal octahedral layer (CrS2)1- stays practically unaltered (Tables 2, 3, 5
and 6). Hydrated products of synthetic NaCrS2 were experimentally studied [49], and later
they were discovered in meteorites as the natural minerals schöllhornite, Na0.3CrS2∙H2O
[12], phases of A and B type ≈ (Na,K)0.07–0.12CrS2∙nH2O [14] and cronusite, Ca0.2CrS2∙(H2O)2
[13]. Caswellsilverite and grokhovskyite in gehlenite paralava are replaced by the poten-
tially new “mineral X” with high Fe content. This process proceeds simultaneously with
pyrrhotite oxidation (Fe source) and through an intermediate phase of schöllhornite-type
(Tables 2 and 3; Figures 2d, 3a and 5b). “Mineral X” has a variable (non-stoichiometric)
composition (Figures 2, 3, 5 and 6), but nevertheless, its composition can be described by
a non-idealized formula {Fe0.3(Ba,Ca)0.2}CrS2∙0.5H2O, whose charge can be balanced only
if all Fe is represented by the Fe2+ cation or the Fe3+(OH)- complex. The appearance of Fe2+
in Fe3+-hydroxide aggregates replacing pyrrhotite is hardly probable, and this mineral
needs further investigation. Schöllhornite was found at the central part of pseudomorphs
of “mineral X” after caswellsilverite (Figure 9) and also as thin zones between the “mineral
X” rim and the caswellsilverite core (Figure 2d). The sum of cations (Na+Sr+Ca+Ba+Fe) in
the intermedium layer of caswellsilverite varied from 0.14 (Na = 0.09) to 0.35 (Na = 0.27)
apfu (Table 5).
The content of water in “mineral X” and caswellsilvertite was calculated on the basis
of microprobe analyses as a difference of a total of 100%. The water content of “mineral
X” is lower than that of caswellsilverite or cronusite. This can be connected both with the
conditions of the microprobe analyses and with genuinely low water concentrations in
altered layered sulphides in a hot desert climate.
In conclusion, the necessary conditions for the appearance of ”meteoritic” chromium
disulphides in terrestrial rock are high chromium content, high temperatures up to ∼1500
°С, low pressure, and high reducing formation conditions, i.e., conditions usually realized
in the processes of meteorite genesis.
Author Contributions: E.V.G. and I.O.G. discovered the layered chromium disulfides, the main
idea of the article, performed the optical and Raman investigation and wrote the article. Y.V. carried
out the fieldwork, geological description and verification of the data. G.Z. performed the micro-
probe analyses. All authors have read and agreed to the published version of the manuscript.
Funding: The investigations were supported by the National Science Center of Poland Grant [grant
number 2021/41/B/ST10/00130].
Data Availability Statement: At the request of other researchers, the authors of the article can pro-
vide the original data.
Figure 16.
Structures of trigonal synthetic layered chromium disulphides, projection on (010):
(
a
) Caswellsilverite analogue [
44
]; (
b
) analogue of potentially new mineral AgCrS
2
[
44
], chromium
occupies tetrahedral sites of the
β
-type, empty circles show vacancy sites of the
α
-type; (
c
) analogue
of grokhovskyite with vacancies in Cr-disulphide layer, fully occupied Cu-tetrahedral sites and
additional Cr-sites (deformed octahedron, green balls) in cation layer [
45
]. Atoms/polyhedra are
shown in green for Cr; dark blue for Cu; light blue for Ag; light yellow for Na; and yellow for S.
Low-temperature alterations of layered chromium disulphides are exclusively re-
flected in changes to the composition and structure of the monovalent cation layer, whereas
the hexagonal octahedral layer (CrS
2
)
1−
stays practically unaltered (Tables 2,3,5and 6). Hy-
drated products of synthetic NaCrS
2
were experimentally studied [
49
], and later they were
discovered in meteorites as the natural minerals schöllhornite, Na
0.3
CrS
2·
H
2
O [
12
], phases
of A and B type
≈
(Na,K)
0.07–0.12
CrS
2·
nH
2
O [
14
] and cronusite, Ca
0.2
CrS
2·
(H
2
O)
2
[
13
].
Caswellsilverite and grokhovskyite in gehlenite paralava are replaced by the potentially
new “mineral X” with high Fe content. This process proceeds simultaneously with
pyrrhotite oxidation (Fe source) and through an intermediate phase of schöllhornite-type
(Tables 2and 3; Figures 2d, 3a and 5b). “Mineral X” has a variable (non-stoichiometric)
composition (Figures 2,3,5and 6), but nevertheless, its composition can be described by a
non-idealized formula {Fe
0.3
(Ba,Ca)
0.2
}CrS
2·
0.5H
2
O, whose charge can be balanced only
if all Fe is represented by the Fe
2+
cation or the Fe
3+
(OH)
−
complex. The appearance of
Fe
2+
in Fe
3+
-hydroxide aggregates replacing pyrrhotite is hardly probable, and this mineral
needs further investigation. Schöllhornite was found at the central part of pseudomorphs

Minerals 2023,13, 381 18 of 20
of “mineral X” after caswellsilverite (Figure 9) and also as thin zones between the “mineral
X” rim and the caswellsilverite core (Figure 2d). The sum of cations (Na+Sr+Ca+Ba+Fe) in
the intermedium layer of caswellsilverite varied from 0.14 (Na = 0.09) to 0.35 (Na = 0.27)
apfu (Table 5).
The content of water in “mineral X” and caswellsilvertite was calculated on the basis
of microprobe analyses as a difference of a total of 100%. The water content of “mineral
X” is lower than that of caswellsilverite or cronusite. This can be connected both with the
conditions of the microprobe analyses and with genuinely low water concentrations in
altered layered sulphides in a hot desert climate.
In conclusion, the necessary conditions for the appearance of ”meteoritic” chromium
disulphides in terrestrial rock are high chromium content, high temperatures
up to ~1500
◦
C, low pressure, and high reducing formation conditions, i.e., conditions
usually realized in the processes of meteorite genesis.
Author Contributions:
E.V.G. and I.O.G. discovered the layered chromium disulfides, the main idea
of the article, performed the optical and Raman investigation and wrote the article. Y.V. carried out
the fieldwork, geological description and verification of the data. G.Z. performed the microprobe
analyses. All authors have read and agreed to the published version of the manuscript.
Funding:
The investigations were supported by the National Science Center of Poland Grant [grant
number 2021/41/B/ST10/00130].
Data Availability Statement:
At the request of other researchers, the authors of the article can
provide the original data.
Acknowledgments:
The authors thank the reviewers for their constructive remarks, which improved
the original manuscript.
Conflicts of Interest: The authors declare no conflict of interest.
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