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C arn d ian M ino alo gi.s
t,
Vol. 12 pp. 104-112
(1973)
ABsrRAc"r
A new proposal
for the nomenclature
of natural Os-
Ir-Ru alloys is presented
as well as compositional
data
for 105 new micro-analyses
of these natural alloys
from Canada"
Territory of Papua and New Guinea,
and Colombia, South America. The minerals re-
ilefined are osmiridium and iridosmine for binary
alioys,
rutheniridosmine
and mthenosmiridium
for ter-
nary alloys,
and compositional
limia are proposed
for
the end members,
native osmium,
native iridium and
native ruthenium.
The fust occunence
of the minerals rutheniridos-
minq -iridiun, and osmium in Canada is reported,
as well as confrrmation
of the occulrence
of osmiri-
dium. The nature of the Os-Ir-Ru alloys from the
Teritory of Papua
and New Guinea
is alic described.
Irrnopucnrox
In the course of a broads investigation of
minerals of the platinum-group elementi (pGE),
currently underway in the Mineral Sciences Divi-
sion, Mines Branch, it was evident that a more
detailed study and an assessment
of the nomen-
clature of the natural alloys of osmium, iridium,
and ruthenium v/as required. Cabri (1972), in a
rgview on the mineralogy of the platinum-group
elements, briefly discussed the existing nomen-
clature of the Os-Ir-Ru system and pointed out
its disadvantages
and inaccuracies.
- This paper reports the results of a study of
the Os-Ir-Ru alloys, some of which w"te mun-
tioned in Cabri's paper, involving 105
new elec-
tron microprobe analyses of natural alloys from
five localities, widely separated in the' rrorld.
These compositions, together with additional data
from the literaturg have enabled us to revise
the nomenclature of the Os-h-Ru wstem. The
proposed
nomenclatwe has been accepted
by the
International Mineralogical Association (IMA)
Commission on New Minerals and Mineral
Names. le additioru the first Canadian occur-
rence of the minerals rutheniridosmine. iridium
E Mineral Research Program * Non-Sulphide Re-
search Contribution No. 34
THE
NOMENCIATURE
OF THE NATURAT
AILOY' OF OSMIUM,
IRIDIIJM
AND RUTHENIUM
BASED
ON NEW COA,IPOS|TIONAI
DATA
OF AttOYS FROM WORTD-WIDE
OCCURRENCES
X
DONALD
C. HARRIS am LOIIS I. CABRI
Mineral Sciences Diuision, Mines Branch, Depafimmt of Energg, Mines anil Resowca"
Ottawa, Ontario, Canada, KIA lGI.
and osmium is reported, and the Canadian occur-
rence of osmiridium is confirmed.
MarsRrA$
Samples of natural Os-h-Ru alloys were ex-
amined from the following localities: Spruce
Creek, British Columbia; Tulameen River, Bri-
tish Columbia; Atlin, British Columbia; Cari-
boo District, British Columbia; Colombia, South
America, and the Territory of Papua and New
Guinea.
Nuggets from the Spruce Creek locality
(U.B.C. No. MA3) and Colombia, South
America
(U.B.C. M1161, Al) were obtained from the
mineral collection, Geology Departrnenl Uni.
versity of British Columbia. A small nugget from
the former Lincoln ming Tulameen River, B.C.
was purchased privately from a collector in the
aIea.
The mineral collections of the Royal Ontario
Museum, Toronto, provided the following speci-
mens in vials containing numerous grains and
were labelled: 10120
'oiridosmine
or osmiridium",
Atlin, B.C.; M12340
"iridosmine", Atlin, B.C.;
M11735 "osmiridium", Ruby Creek, Atlin, B.C.;
M14274 o'platinum"o Bullion, Kariboo District,
B.C. (modern spelling "Cariboo") ; MI24I0
ooplatinum", above junction of Bear Creek on
Tulameen River,
Tulameen, B.C.
;MlM77'"plat-
inum", Granite Cree( B.C. ; M12339
ooplatinum",
Discovery Atlin, B.C., 10120
"iridosmine", Atlin,
B.C. Only a few grains from each vial were
mounted and polished for examination.
The Atlin district is in the northwest corner
of British Columbia, adjacent to the Yukon Ter-
ritory. This district produced about $15 million
of gold between 1898
and lg46 and $1 million
between 1946
and 1953. The town of Discovsy
is on the north banl of Pine Creek, which con-
nects Surprise Lake with Atlin Lake. Ruby Creek
drains into Surprise Lake and iridosmine from
Ruby Creek is the only mineral of the platinum
group that had prwiously been reported from
this area (Gledhill l92I). Spruce Cre& is a
104
THE NO]VIENCLATURE OF THE NATURAL ALLOYS OF OSMIUM r05
tributary of Pine Creek and may be the Spruce
Creek from which the sample
of the U.B.C. col-
lection (No. MA3) originated. Numerous out-
crops of ultramafic and mafic intrusions, refer-
red to as fhe "Atlin intrusions" (Aitken 1959),
occur associated with Paleozoic greenstones in
the area between the town of Atlin and Surprise
Lake as well as to the north of Surprise Lake
in the headland of Ruby Creek.
Platinum and "osmiridium'o have been re-
ported from the Quesnel River area, Cariboo
Mining Division, about 350 km due north of
Hope, B.C. This area is noted mainly for its
gold production. The history and some details
of assays reporting platinum, palladium and
"osmiridium" from the Bullion mine are given
by O'Neill & Gunning (1934). This may be the
locality from rvhich ROM sample M14274 was
obtained.
The geologr of the Tulameen River area, in
south-central British Columbia, has been de.
scribed by Camsell (1913) ; Rice (1947) has
summarized the origin, history, and description
of its gold and platinum-bearing placers. The
petrology and origin of the ultramafic Tulameen
layered complex, discussed
by Findlay (1969),
is considered to be a ooconcentric"
intrusion (Jack-
son & Thayer 1972). Early assays for "platinum"
nuggets,
tabulated by Rice (1947) and O'Neill &
Gunning (1934), reported
mainly platinum with
minor quantities of "osmiridium", palladium,
osmium, and rhodium. The Lincoln mine is
thought to have been located about half a mile
below the mouth of Britton Creek (formerly
Eagle Creek).
The grains from British Columbia are between
200 p.:n (sample M12339,
gr. 5) and about 2 mm
(sample M12340, gr. 6) in diameter. They are
usually rounded to sub-rounded
with a metallic
lustre. A few grains of iridosmine are hexagonal
in cross
section (e.g.
sample M12339,
gr. 1). The
Os-Ir-Ru minerals were always found in the
non-magnetic fractions (hand magnet).
Many inclusions were observed even though
several of tle grains appeared free of inclusions
in polished sections. Most common were iron-
bearing platinum, irarsite (hAsS), and osmian
irarsite.
hidosmine occurs with osmiridium in two
grains (samples
10120,
9.2 and M12339,
gr. l).
The first of these is shown in Figure I with
minor irarsite (hAsS) ; the second grain occurs
as a small (16 X X-pm) inclusion in an iridos-
mine matrix rvhich is hexagonal in cross
section.
Iridosmine was also found as laths in iron-
bearing platinum, (e.g. sample MlM77, gt. I,
8 X 93-pm lath and, in the Lincoln mine sam-
ple, as a25 X 100-pm lath). Omium was found
as a large homogeneous inclusion-free grain
(M12340, gr. 6, 1.5
X 2 mm) and as a lath
(i0 X 100-pm in a grain of iron-bearing plati-
Frc. L Photomicrograph of a nugget from Atlin, B.C.
(10120 gr. 2) showing iridosmine (light sey) in
contact with osmiridium (medium grey). Finely
disseminated irarsite rims and partly replaces the
iridosmine.
Frc. 2. Photomicrograph showing inclusions of iridium
(light grey) in a matrix of iron-bearing platinum.
The nugget is from Bear Cree\ B.C. (M12410,
s.4).
Frc. 3. Photomicrograph showing curved veinlets ol
'oosmiridium" (light grey) in a matrix of ruthen-
iridosmine (Ml2g0, gr. 2, Atlin, B.C.).
r06 THE CANADIAN MINERAIJOCIST
num, M11735" g. 4). hidium was observed as
numerous inclusions in a matrix of iron-bearing
platinum (M12410, gr. 4, shown in Fig. 2). In
one case, rutheniridosmine was found to contain
curved veins of what was tentatively identified
as osmiridium (Fig. 3).
The New Guinea material, originally labelled
as 'oosmiridium", was purchased in the early
1960's from Johnson,
Matthey and Mallory Ltd.,
Montreal. The exact origin of tlle material is
uncertain, but information obtained lrom the
company's
associate
in Australia states
"The ma-
terial rvas probably found by the natives rrhen
they were gold prospecting
and more than likely
has been pidced out by hand from alluvial
gold. . . . The material was delivered to the Bank
at Port Moresby." Correspondence
(9/3/72) with
Nfu. A. Renwick, Chief Government Geologist,
Territory of Papua and New Guinea, states that
"It is almost certain that the osmiridium referred
to comes from the Ioma area of the northern
district of Papua. . . . The area lies within the
Papuaa Ultramafic Belt." According to Davies
(1968), who has studied trhe area in detail, our
material could have come from either the Waria
River (Bowutu Mountains) or the Yodda Gold-
field, part of the broad Papua Ultramafic Belt.
The concentrate consists of several hundred
nuggets ranging from I00 pm up to 2 mm in di-
ameter. The nuggets occur in various shapes
from rounded to flattened irregular forms to
tabular, short, hexagonal-prismatic crystals. A
few of the nuggets occur as tlin cleavage flakes
derived from larger pieces, though a few have
a spongy appearance. Under a binocular micro-
scope,
the material has a metallic luster varying
from a dull mat finish to smooth, bright {0001}
cleavage
planes; however, most of the grains are
steel grey. Numerous inclusions of iron-bearing
platinum, irarsite, laurite and two unidentified
ruthenian and iridian arsenides
were observed
and these will be described in another note in
preparation.
MrrHot oF TNVEsTIGATIoN
The individual nuggets \Mere mounted in cold
setting Araldite (several to a section), polished
on water-cooled lead laps with final buffing
using MgO. The sections 'were examined under
an ore microscope and analyzed with a Materials
Analysis Company microprobe. The normal cor-
rections to the r-ray intensity data were made
with a computer prograln of Rucllidge & Gas-
parrini (1969), revised and updated. Each grain
lvas analyzed for nine elements
using the follow-
ing standards and r-ray lines: iridium metal
h.L.,, osmium metal Os.Lo, ruthenium metal
RuZd, palladium metal Pdlo, copper metal
CuK- nickel metal NiK- iron metal FeKo, a
PtgoRha alloy Ptl.,, Rhlo. Allowances were
made for the enhancement of CuK., intensities
by iridium and slits were used to improve the
peak/ba&ground of osmium and iridium. Since
the pure ruthenium and osmium ctuld be ob-
tained in powder form only, a chemical vapow
transport technique was used to recrystallize
the
material into coarser
fragments.
Op:rcal Pnoppnrrss aNo CnvsreLLocRAPI{Y
Osmium, iridosmine, and rutheniridosmine are
rn'hite,
with a bluish grey tinge in reflected
light.
They are weakly to moderately
anisotropig some-
times exhibiting waly extinction, but bireflec-
tance is weak to absent.
Iridium and osmiridium
are white, vdth a cream-coloured
tinge, in re-
flected light. Both are isotropic.
The bluish white
colour of the hexagonal anisotropic minerals is
enhanced, as is the cream-white colour of the
isotropic
minerals,
when they occur
together.
The
bluish white coloru of the anisotropic minerals
is also enhanced when they occur with white
iron-bearing platinum.
The crystal system of pure osmium and ruthe'
nium has long been known to be hexagonal
whereas
pure iridium is cubic. The x-ray diffrac-
tion data and unit cell dimensions
are listed in
the PD File as folloq/s:
File No.
Symmetry
Soace sroup
aA
cA
Osmium Ruthenium lridium
6-0662 6-0663 6-0598
Ho<agonal Hexagonal Cubic
P6s/rnmc P6s/mrnc FmSm
2.7Ut 2.7058 3.8394
4.3197 42819
The syrnmetry of natural compositions was
confirmed by x-ray powder patterns using a
5'1.3-mm-diameter
Gandolfi camera.
X-ray pow-
der patterns were obtained for two compositions
(indicated in Table 1) of rutheniridosmine
lrom the Territory of Papua and New Guinea,
of iridosmine, 8r. 1, Spruce Creek, 8.C., and of
o-.miridium, gr. 5, Spruce
Creek, B.C.
Determination of the unit cell dimension of
this iridosmine gave a 2.724, c 4.333A whereas
the osmiridium gave 4 3.8224. A11 the natural
alloys of rutheniridosmine are hexagonal and
isomorphous with pure osmium and ruthenium
in spite of minor substitution of other elements.
Couposrrrows oF THE Nerunar- Os-Ir-Ru Ar.r.ovs
The results
of the electron
microprobe
analyses
of the natural Os-h-Ru alloys are listed in
Table 1. These analyses, with others taken from
TIIE NOMENCLATURE OF THE NATURAL ALLOYS OF OSMIU]VI
Ru
107
tr SPRUCE
CK- B.C.
0 cauronrun
@LOMBIA
0 unmowru
l. JAPAN
A URALS
Os IRIDOSMINE
Pt
the literatwe, are plotted in Figure 4. The com-
positions plotted have been recalculated
to atomic
per cent, based on the tlree major elements, and
are given in Table 1. The compositions used
from the literature are the same as reported by
Cabri (1972). The sources
of the daia ate as
follows : California (Snetsinger
1971), unlnown
(L6vy & Picot 1961), Japan (Aoyama 1936),
Urals (L6vy & Picot 1961
; Westland & Beamish
1958) southeast Bomeo (Stumpfl & Clark 1966)
and Brazil (L6vy & Pimt 1961).
These composi-
tions were considered the most reliable of the
numerous analyses quoted in the literaturg con-
sidering the completeness and method of analysis
and the size and microscopic descriptions of the
nuggets. Even then, one must accept the analyses
with caution because many of the nuggets ex-
amined in this study were found to consist of
more than one phase for which the microprobe
must be considered
the most reliable method of
analysis.
TULAMEEN
R" BC.-i*
NEW
GUINEA
.
SE BORNEO
g
BULL|oN,BC
o/
BRAZL/D\
ATUN,B.C
O
lr
%
Pt
Frc. 4. Natural Os-Ir-Ru and Os-Ir-Pt minerals from this study and from the
Iiterature. The two analyses hom Granite Creelq B.C, (see Table 1) have
been plotted with the symbol for Tulameen River because Granite Creek is
one of its tributaries. The four compositions indicated with an ar"ow repre-
sent two sets of co-erdsting iridosmine and osmiridium. The tlree composi-
tions labelled "Il'signify a lath
Subsequent
to writing this paper, additional
microprobe analyses
of natural Os-h-Ru alloys
from Borneo by Stumpfl & Tarkian (1973) were
found to be consistent with our data.
THs TTRNARy SvsrsM Os-Ir-Ru
Work in the synthetic Os-Ir qystem
by Vacher
et al. (1954) and by Rudman (1967) has indi-
cated that a miscibility gap exists, though its
boundaries have not been precisely
defined.
Raub
(1964) showed that in the Ru-h qystem
a mis-
cibility gap exists from 45 to 57 atomic % Tr at
1300'C and widcns at lower tempoatures. Raub
(1959) reported complete hexagonal solid solu-
tion for the Os-Ru binary. Our analytical results
(Table 1) of natural Os-h-Ru alloys with addi-
tional data from the literature has enabled us to
more precisely define the boundaries (Fig. 4).
The cubic alloy extends from 100 atomic /s to
about 62 atomic /6 k, whueas the hexagonal
THE CANADIAN
108
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E
110 T}IE CANADIAN MINEP,AI.OGIST
alloy octends from 100 atomic % to about 55
atomic /e Os. These new boundaries for the mis-
cibility gap are slightly changed from Cabri's
(1972) proposal
because
of the larger number oI
analyses now available. In particular, two sam-
ples ftom Atlin, B.C., which mnsist of co-existing
hexagonal
and cubic ternary alloys, help to define
the boundary along the Os-Ir join. These co-
existing grains are indicated with arrows point-
ing to the locality symbol in Figure 4. The two
phase field extends into the Pt-Os-h system, as
shown in Figure 4, and must intercept the Os-Pt
binary at a position which has not yet been
exactly determined. This is assumed because it
is unlikely that a solid solution exists between
hexagonal osmium and cubic platinum. On the
other hand, it is probable that complete solid
solution exists between cubic iridium and cubic
platinum.
NoMsNcrdruRn FoR NATUnAL
Os-Ir-Ru Arr.ovs
An excellent historical review on the nomen-
clature of natural Os-h alloys vras made by Hey
(1963). From this review, he suggested that the
most suitable nomenclature for the natural Os-h
alloys, now in common usage,
be the following:
For the cubic alloys ; osmiridium with Os < 32
at.%
For the hexagonal alloys: iridosmine with
32<Os<80 at /e
Native osmium for Os > 80 x. /o
The name ruthenosmiridium was proposed
by
Aoyama (1936) for a hexagonal Os-h-Ru natural
alloy with composition RuOsIr. Strunz (1966)
howeve, introduced the term ruth,en-iridosmium
for Aoyama's mineral. In this study, it has been
shown (Fig. 4) that there is a very extensive
range of compositions for hexagonal Ru-Os-h
alloys. The name ruthenosmiridium proposed by
Aoyama is unfortunate because it includes the
term "osmiridium", which from Hey's proposal"
is associated with cubic alloys. Based on our
analytical results, it is obvious that the names
osmiridium and iridosmine should be re-defined
to make provision for a miscibility gap in the
Os-Ir system and also to provide flexibility for
the solid solution of specific
maximum quantities
of other platinum-group elements.
It is also
neces-
sary to re-examine the nomenclature for hexa-
gonal ternary alloys and to propose a name for
cubic ternary alloys. At the same time, uniform
definitions are proposed
for the native metal end-
members and alloys along the Os-Ru and Ir-Ru
binary joins.
Our proposals
for alloys in the Os-h-Ru system
are that:
a) the name osmium is for hexagonal alloys with
\ 80 at. To Os;
b) the name iridium is for cubic alloys with
s80 at.
% h;
c) the name ruthenium is for hexagonal alloys
with = 80 at. To Ru;
d) the name ruthenosrniridium of Aoyama
(1936) be applied to cubic (h, Os, Ru)
alloys, where Ir < 80 at. % of (Ir * Ru *
Os) and Ru > 10 at. /6 ot (Ir * Ru * Os) ;
also with no single other element
> L0 at. /6
of total;
e) Iridosmine of Hey (1963) be redefined as
hexagonal
(Os, h) alloys with no single other
element > l0 at. /o of total, and where Os
< 80 at. % of (Os * k) ; the presence
of the
miscibility gap defines the other boundary at
approximately 55 at. % Os;
t) Osmiridium of Hey (1963) be redefined as
cubic (Ir, Os) alloys with no single other
element > 10 at. /o of. total, and where Ir
< 80 at. % of (k * Os) ; again the misci-
bility gap limits the field to approximately
62 at % Ir;
e) Rutheniridosmine or ruthen-iridosmium of
Strunz (1966) be re.defined as hexagonal
(Os, h, Ru) alloys where Os < 80 at. /6 of
(Os * Ir * Ru) and Ru is 10 to 80 at. /6 ot
(Os *Ir * Ru), also where no single other
element
> l0 at. % ol totaT; and
h) to be consistent with our proposal on the
binaty join Os-h, similar lines must be
drawn parallel to the Ru-Os and Ru-h
edges; these alloys would not require new
names, but using Schaller's (1930) adjectival
modifiers these compositions may be simply
known as ruthenian osntiunt, osmian ruthe-
niurn, iridian ruthenium, and ruthenian hi-
dium i these fields would have similar bound-
aries (where no single other element ) 10
at. % of total) as
proposed
for iridosmine and
osmiridium; for the former two minerals, the
boundary between them is arbitrarily taken
at 50 at. /e Os whereas the boundary between
the latter two minerals is as defined by the
miscibility gap, i.e., to a minimum 57 a't. %
Ir for ruthenian iridiurn and to a minimum
of 55 at. % Ru for iridian ruthenium.
Drscus$or.r oN TlrE pRoposED
Nolrnucr-eruru
oF TtrE Os-Ir-Ru Ar.r.ovs
Several noteworthy comments made by mem-
bers of the Commission on New Minerals and
Mineral Names (IMA) descve some discussion
ilr order to avoid possible confusion by other
workers. The questions raised were: (a) Is it
necessary to introduce so many names when per-
THE NOMENCLATURE OF TIIE NATURAL ALLOYS OF OSMIUM 111
haps four are sufficient ? (b) Why are special
names needed for iridosmine and osrniridium
and should not the names nevyanskite
(Ir > Os)
ar:d sysertskite
(Os > h) be retained ? (c) Is the
distinction of. rutheniridosmine lrom iridosmine
easy to make by using their physical properties
?
(d) Should new narnes like rutheniurn be pro-
posed if no occur"ence
has been found ? (e)
Should not the proposed
rutheniridosmine field
be further subdivided because,
in its present form,
a mineral with79% Os will bear the same
name
as a mineral wlth79/p Ru ? (f) Should not lines
be drawn parallel to the Ru-Os and Ru-h edges
ao drawn for the Ir-Os edge ?
In reply to the above questions, we feel that
our proposed
nomenclature has not introduced
new or additional names, but is simply a r+defi.
nition of names existing in the literature. Special
names suclr as iridosmine and osmiridiurft were
suitably discussed
by Hey (1963) and are
retained
as more descriptive than such names as nevyan-
skite and sysertskite.
It is necessary
to give a dif-
ferent name or names for the higher Ru-bearing
alloys because
iridosmine and osmiridium are
traditionally known as binarg alloys. The dis-
tinction ol irido:mine fuom rutheniridosrnine is
not easy because both minerals are hexagonal
and have similar optical and x-ray properties.
Our proposed nomenclattue is based on com-
position because many of these alloys occur as
small composite grains suitable only for electron
microprobe analysis.
The field proposed
for ru'
tlrcnhidosmine is large, unfortunately, but we
feel that further subdivision of this field would
lead to more confusion and would require too
many names, not to mention more accurate com-
positional data. We agree that compositions
occnrring in the field at ruthenium and ruthenos-
miridium have not yet been found in nature.
The latter name is suggested
as a redefinition
because it, likewisg is a good descriptive
name,
whereas
rutltenium is the most logical name for
the ruthenium end-member. Our original propo-
sal, submitted to the Commission, did not in-
clude boundary lines parallel to the Ru-Os and
Ru-Ir edges.
This noteworthy suggestion by the
Commission has been incorporated in our pre-
sent proposal,
and, using Schaller's (1930) adjec-
tival modifiers, these compositions may be simply
known as ruthenian osmium, osntian ruthenium,
iridian ruthenium, and ruthen'ian iridium. These
fields would have similar boundaries
(< I0 at, /6
etc.) to those proposed
for iridosmine and os-
mhidium.
After sufficient data are available a similar
rype of nomenclature can be applied to other
ternary systems such as the Pt-Os-h system.
From our present sfridy, ternarg cubic and hexa-
gonal alloys with Pt > l0 at. % can be expected
tc occur ; they would require new species
names
similar to ruthenosmiridium, and rutheniridos-
mine, for example, platinosmiridium and plati-
niridosming respectively.
AcrwowuoceMm.ITs
We are grateful for samples
to Drs. J. A. Man-
darino and R.I. Gait of the Royal Ontario Mu-
seum and to Mr. J. Haight of the Departrnent
of Geology, University of British Columbia,,for
the Spruce Creek and Colombia samples.
We
thank- the following personnel of the Mineral
Sciences
Division for assistance
: Mr. I. H. G. La-
flamme for some quantitative probe analyses
and
for the difficult polished sections, Dr. A. H.
Webster for recrystallization of Ru and Os pow-
ders, Mr. J. M. Stewart for the r-ray diffraction
analyses
and Mr. R. G. Pinard for photomicro'
graphs.
'We are grateful to the various mernbers of
the Commission of New Minerals and Mineral
Na-es for useful suggestions,
and especially
thank Dr. M. Hey of the British Museum fior
reviewing our proposal before its submission to
the Commission.
RsrnnENces
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Marutscript receh;eil
March 1973.
