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Composition of eudialyte group minerals in the Sagåsen pegmatite, data from Table 3b. The grey fields are the ranges of eudialyte group minerals in Langesundsfjord suite pegmatites analysed by Andersen et al. (2010), grey rhombs are analyses from the Sågåsen pegmatite by Larsen et al. (2005).
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Agpaitic nepheline syenites have complex, Na-Ca-Zr-Ti minerals as the main hosts for zirconium and titanium, rather than zircon and titanite, which are characteristic for miaskitic rocks. The transition from a miaskitic to an agpaitic crystallization regime in silica-undersaturated magma has traditionally been related to increasing peralkalinity of...
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... has been analysed in two samples (E1, E3) from the Sagåsen pegmatite, which supplements analyses from Langesundsfjord suite pegmatites published by Andersen et al. (2010), and analyses from Sagåsen itself including minor and trace components by Larsen et al. (2005). Compared to the analyses published by Andersen et al. (2010), the present eudialytes (Table 3b) have clearly higher Mn/(Mn+Fe) ratio, lower Si M(3) and lower combined vacancies and H 3 O + in the N-position (Fig. 4). An appropriate characterization of the mineral in terms of endmembers would be "feklichevite-zirsilite solid solution", with some domains ranging towards kentbrooksite. ...
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... Згідно з даними (Andersen et al., 2013;Schilling et al., 2009), зі зниженням температури розплаву і збільшенням активності Nа та летких компонентів (F, СО 2 і Н 2 О) область кристалізації ринкіту-(Се) розширюється (оскільки для гетценіту такі дані відсутні, передбачаємо, що їх можна екстраполювати на усі мінерали групи ринкіту). Враховуючи асоціацію породоутворювальних мінералів, а також мінерали, які спостерігаються як зрос тання або включення в гетценіті (флюорит, ілерит, кальцит, натроліт, стронціаніт, флюоркафіт, катаплеїт), ортомагматичні флюї ди початкового розплаву(ів) були насичені як лугами, так і леткими компонентами (особливо F). ...
The nepheline syenites of the Pokrovo-Kyriyivo massif in the junction zone of the Dnieper-Donets Rift and the Priazoviаn block of the Ukrainian Shield contain numerous of rare-metal minerals, among them götzenite is the most common. The nepheline syenites are divided into malignites (melanocratic, early) and juvites (leucocratic, late) based on their mineralogical characteristics. In both varieties, the götzenite is presented as euhedral or subhedral grains with a poikilitic texture (numerous rounded inclusions of nepheline). Among rock-forming minerals are observed feldspar, annite, aegirine (± alkaline amphibole), titanite, strontianite ± sodalite ± cancrinite ± Sr-apatite ± calcite ± natrolite. Usually götzenite in malignites has a 'patchy' zonation due to the presence of metasomatically altered areas in the central parts, which have a lower content of Ca, Na, Sr and F, and a higher Si, relative to the outer parts. In comparation to juvite, the götzenite of malignite is more enriched in Zr, Nb and REE, with a low Y content in both types of rocks. A notable feature of the götzenite is high Sr content (up to 3 wt. % SrO), but low Nb (often up to 1.3 wt. % Nb2O5) and REE (often up to 2.4, rarely up to 5.6 wt. % REE2O3). The occurrence of götzenite in nepheline syenites of the Pokrovo-Kyriyivo massif is related with the early stage of the alkaline silicate melt differentiation with increasing activity of Na and volatile components, especially F. During götzenite crystallization the majority of REE and HFSE remained in the fluid as soluble complexes and precipitate own minerals at the postmagmatic stage. This is confirmed by presence of fine inclusions of fluorobritholite-(Ce), strontianite and burbankite in cleavage fractures, in miarole-like inclusions — aeschynite-(Ce), pyrochlore group mineral, bastnaesite, burbankite, etc. The Sr enrichment of götzenite can be explained by early crystallization from an Sr-enriched alkaline silicate melt and the absence of another Ca-rich rock-forming minerals or by external introduction of CO2-F fluids enriched in Sr and REE separated from a carbonatite melt.
... The deposits are characterized by complex mineralogy. The most common primary hosts for Nb, Zr and REE are eudialyte group minerals, loparite, apatite, titanite, rinkite group minerals, zircon or baddeleyite, and wöhlerite group minerals (Marks et al., 2008;Andersen et al., 2010;Andersen et al., 2013;Linnen et al., 2014;Tukiainen, 2014;Kalashnikov et al., 2016;Marks and Markl, 2017). Table 1 lists the Zr and Nb minerals mentioned in text and tables including their formulas and typical occurrences. ...
... The deposits in feldspathoid syenites and those in peralkaline granites are evidence that the solubilities of HFSE and REE minerals in peralkaline silicate melts must be unusually high, which indicates drastic changes in the mechanism of HFSE and REE dissolution compared to that in aluminosilicate melts without excess of alkalis. Important parameters causing this may include peralkalinity, halogen and water contents, temperature of the magma, and perhaps silica activity as indicated by pronounced differences in mineralogy between silica-saturated and silica-undersaturated rocks (Kynicky et al., 2011;Andersen et al., 2013;Marks and Markl, 2017). However, little is known from experiments, particularly at silicaundersaturated conditions, with the exception of the solubilities of zircon (ZrSiO 4 ), columbite-(Mn) (MnNb 2 O 6 ), and tantalite-(Mn) (MnTa 2 O 6 ) in felsic melts, which are fairly well studied. ...
... This is highly important not only for a better understanding of the formation of magmatic Zr and Nb deposits, but also for the interpretation of trace element data, for which Nb and Zr are often Table 1 Zirconium and niobium minerals mentioned in text and tables, with typical occurrence in miaskitic, agpaitic, or hyperagpaitic peralkaline (Marks and Markl 2017) taken as reference elements because of their immobility at most conditions. The stability field of wöhlerite in a H2O -a HF -a Na2Si2O5 space is fairly small (Andersen et al., 2010;Andersen et al., 2013), thus reaction with alkali silicate melts may produce other Zr and Nb phases. As an additional result, our study may then provide tentative information on Zrand Nb-mineral stabilities. ...
The solubility of w¨ohlerite, ideally Na2Ca4ZrNb(Si2O7)2O3F, in peralkaline SiO2-undersaturated melts
(Na2O–CaO–Al2O3–SiO2 ± F ± H2O) was studied at the following temperature (T) and pressure (P) conditions:
750 ◦C, 200 MPa, 850 ◦C, 100 MPa, and 1000 ◦C, 200 MPa. W¨ohlerite appeared to be stable up to high temperature,
with increasing solubility, which is consistent with field observations of early w¨ohlerite crystallization
in pegmatites in the Larvik Plutonic Complex. A lovozerite-group mineral (combeite–zirsinalite–lovozerite) was
frequently observed to crystallize in the experiments at 750 ◦C, and, at very high Na/Al ratios, also at 850 ◦C.
Fluorcalciopyrochlore formed at 1000 ◦C in experiments where water was added. The concentrations of Zr and
Nb in the quenched glasses were generally very high and found to increase strongly with temperature. Moreover,
they also increase with addition of water and with increasing peralkalinity. The effect of CaF2 addition was
insignificant. Based on comparison with the limited information in the available literature, the solubilities of Cabearing
Zr and Nb minerals (w¨ohlerite, lovozerite-group minerals, fluorcalciopyrochlore) in peralkaline silicaundersaturated
melts may be lower than those of nominally Ca-free Zr and Nb minerals (zircon, baddeleyite, wadeite, columbite-(Mn)). The experimental data do not support the existence of significant Zr–F or Nb–F complexation. The high concentrations of Nb and Zr in the reacted peralkaline melts can be explained by strongly
enhanced formation of alkali-Nb/Zr-silicate complexes compared to that at peraluminous conditions. These complexes are the underlying chemical reason for characteristic high-field-strength-element (HFSE) enrichment
in agpaitic and hyperagpaitic rocks.
... The occurrence of these minerals defines the so-called agpaitic rocks, as opposed to miaskitic rocks, where minerals as zircon, titanite, and ilmenite are the main Zr -Ti sinks (Marks and Markl, 2017;Sørensen, 1997). Among the agpaitic minerals, astrophyllite is an important HFSE-bearing accessory in a diversity of nepheline syenites (Andersen et al., 2013;Macdonald and Saunders, 1973;Piilonen et al., 2003b), peralkaline granites (Abdel-Rahman, 1992;Birkett et al., 1996;Marks et al., 2003), and related pegmatites (Layne et al., 1982;Macdonald et al., 2007;Macdonald and Saunders, 1973), and less commonly in silicic subvolcanic rocks (Žáček et al., 2016). Astrophyllite crystallizes in these rocks during late-magmatic and/or post-magmatic stages, and shows significant compositional variability, which allows monitoring and estimating some extensive and intensive parameters of its crystallization environments such as fluid compositions, T, f O2 , and aH 2 O (Abdel-Rahman, 1992;Piilonen et al., 2003b;Piilonen et al., 2004). ...
... Zoned crystals show increasing Ti (up to 1.68 apfu) and decreasing Zr (0.19 apfu) and Nb (0.05 apfu) towards crystal rims (see Tables 2 and S1). As compared with typical astrophyllite from other occurrences (Fig. 5b), MAN Ast-1 shares similar compositions with astrophyllite from nepheline syenite pegmatites in the Oslo Rift Valley (Andersen et al., 2013), alkaline metasomatites in the Oktyabrsky Massif (Kryvdik et al., 2011), and rhyolite dikes in the Mongolian Altai (Žáček et al., 2016). Furthermore, the zoned MAN Ast-1 depicted in Fig. 4g shows a well-marked compositional gap between the main crystal and the darker rims with higher Zr/Nb ratios, similar to post-magmatic astrophyllite compositions from the Strange Lake peralkaline granites (Piilonen et al., 2003a). ...
... Among the Ast-2 groups, the MAN and PAP Ast-2b crystals have relatively high average Ti values (up to 1.76 and 1.98 apfu, respectively), whereas Zr and Nb contents are down to 0.02 and 0.01 (apfu), respectively (Tables 1 and S1). Overall, the compositions of the postmagmatic Ast-2b group overlap those registered by Piilonen et al. (2003a) in post-magmatic astrophyllite crystals from pegmatites in the Kangerdlugssuaq Intrusion, and from nepheline syenite pegmatites in the Khibina Massif and in the Oslo Rift Valley (Andersen et al., 2013;Piilonen et al., 2003a). The MAN Ast-2a group has intermediate Ti (up to 1.80 apfu) and Nb + Zr (up to 0.37 apfu) abundances when compared to Ast-1 and Ast-2b, and these are comparable to the compositions of postmagmatic astrophyllite from pegmatitic dykes in the Kangerdlugssuaq Intrusion (Layne et al., 1982;Piilonen et al., 2003a). ...
Astrophyllite is a common “agpaitic” accessory mineral in evolved peralkaline alkali feldspar granites from the Mandira and Papanduva plutons in the Graciosa Province (S-SE Brazil). Textural and in-situ chemical (major and trace element) data provide new insights on the mechanism of formation and evolution of astrophyllite in magmatic and post-magmatic environments. Magmatic astrophyllite forms isolated or aggregates of micaceous crystals that, in part, co-precipitated with sodic amphiboles (arfvedsonite and riebeckite) and aegirine, and with Tisingle bondZrsingle bond and/or REE-rich accessories. It presents relatively Nb- and Zr-rich and Ti-poor compositions and the Mn contents are significantly higher in the Papanduva crystals. These crystals have significant REEs contents (up to 3949 ppm), and efforts were made to obtain rough estimates for the REEs partition coefficients (ast/meltDREE) between astrophyllite and modeled evolved melts to examine their controls. Except for Nd to Tb, the calculated ast/meltDREE are higher for the Na-richer crystals from the Mandira samples, suggesting a crystal chemical control on their partitioning, especially the preference of trivalent REEs to charge-balance Na+ incorporation by the coupled substitution Na+ + REE3+ ↔ 2Ca2+. Lattice strain modeling supports the entrance of the REEs mainly in the [10]B cationic site of the astrophyllite structure. Post-magmatic astrophyllite occurs mainly as acicular and radiating crystals by replacing magmatic arfvedsonite, riebeckite, and aegirine. They are Ti-rich, close to the ideal end member, with lower Zr, Hf, Th, U, Nb, Ta, Ga, Li, Sc, Y, and REE contents than the primary crystals. Their formation occurred mainly via disequilibrium processes and substitution reactions of early sodic amphiboles and clinopyroxenes triggered by the circulation of relatively K- and Ti-rich hydrothermal fluids. Compositional variations between both the astrophyllite groups reveal that the parameters Zr/(Zr + Ti) and Mn/(Mn + Fe) can be used as chemical indicators to discriminate magmatic and post-magmatic (hydrothermal) crystallization environments, as well as to evaluate their redox conditions.
... Zr-bearing accessory minerals form over a very large P -T (pressure and temperature) range and in a wide variety of lithologies. The stability of these minerals relative to their host rock compositions and to other Zr-bearing phases is complex and variable (e.g., Marks et al., 2011;Andersen et al., 2013). Relatively little is known of the factors controlling the distribution of the phases, and the textural relationships between them are often poorly documented. ...
The mineral occurrences, parageneses, textures, and compositions of
Zr-bearing accessory minerals in a suite of UK Paleogene granites from
Scotland and Northern Ireland are described. Baddeleyite, zirconolite, and
zircon, in that sequence, formed in hornblende + biotite granites (type 1)
and hedenbergite–fayalite granites (type 2). The peralkaline microgranite
(type 3) of Ailsa Craig contains zircon, dalyite, a eudialyte-group mineral,
a fibrous phase which is possibly lemoynite, and Zr-bearing aegirine.
Hydrothermal zircon is also present in all three granite types and documents
the transition from a silicate-melt environment to an incompatible
element-rich aqueous-dominated fluid. No textures indicative of inherited
zircon were observed. The minerals crystallized in stages from magmatic
through late-magmatic to hydrothermal. The zirconolite and eudialyte-group
mineral are notably Y+REE-rich (REE signifies rare earth element). The crystallization sequence of the
minerals may have been related to the activities of Si and Ca, to melt
peralkalinity, and to local disequilibrium.
... The compositions of all these accessory minerals are in Supplementary Table S14. (Melluso et al., 2014), Phlegrean Fields , Gharyan (Lustrino et al., 2012), Sushina Hill (Chakrabarty et al., 2018), Itatiaia , Passa Quatro (Guarino et al., 2019) and Oslo Rift nepheline syenites (Andersen et al., 2010(Andersen et al., , 2012]. The reference compositions of rinkite-and wöhlerite-groups are from the Handbook of Mineralogy and MINDAT. ...
The Late Cretaceous (~78 Ma) Poços de Caldas massif is the largest alkaline complex in Brazil and the second in the world by extension (>800 km²). It is considered the westernmost outcrop of the Cabo Frio magmatic lineament, in the northern sector of Serra do Mar potassic-ultrapotassic igneous province, central-eastern Brazil. The outcropping rocks are peralkaline phonolites (~80%) and nepheline syenites (~15%) with rarer (<5%) basic-ultrabasic rocks (leucite basanites, basanites, basalts and lamprophyres). The phonolites have different levels of volatile (F and Cl) and other trace elements, which tend to decrease with increasing evolution, due to removal of F-, Mn-, HFSE- and REE-rich accessory phases accompanying cotectic alkali feldspar and nepheline. The geochemical variability of titanite, eudialyte, F-disilicates, aenigmatite, lamprophyllite, clinopyroxene, amphibole and other phases indicate the effects of removal of accessory phases and the presence of independent liquid lines of descent in the various intrusive pulses. The initial Sr−Nd isotopic ratios of the basic-ultrabasic lavas [⁸⁷Sr/⁸⁶Sri = 0.70440–0.70498; εNdi = −3.7 to −1.2] are within the range of the other Late Cretaceous-Paleogene rocks of the northern sector of Serra do Mar, indicating a highly metasomatized K-rich lithospheric source. Nepheline syenites and phonolites have SrNd isotopes largely overlapping with that of the basic-ultrabasic lavas (⁸⁷Sr/⁸⁶Sri = 0.70503–0.70540 and εNdi = −3.9 to −2.5 for nepheline syenites; ⁸⁷Sr/⁸⁶Sri = 0.70511–0.70527 and εNdi = −3.4 to −3.2 for phonolites). Prolonged fractional crystallization processes dominated by clinopyroxene removal from melts with compositions resembling those of the basic-ultrabasic compositions can produce residual liquids qualitatively comparable with those represented by the phonolites and nepheline syenites.
... From nepheline syenite to nepheline syenite pegmatite, the melt crystallization temperature decreases from about 700 8C to less than 500 8C, and the melt composition becomes more reduced with sodium, halogen, and water enrichment (as deduced from mineral compositions) and the presence of fluorite (Fig. 3). According to chemographic analyses (Andersen et al. 2013, Andersen & Friis, 2015, the lower temperature and stronger activities of sodium, halogen, and water allow the extensive crystallization of rinkite-(Ce) in the late pegmatitic stage of the Saima complex through fractional crystallization of nepheline syenite melts. The compositional variations of rinkite-group minerals from different stages in Figure 7 suggest the compositional changes of evolving alkaline melts, and that REEs (especially HREE) are preferentially partitioned into the residual alkaline melts due to their incompatible behaviors. ...
... In contrast to Slepnev (1957) and Sokolova & Hawthorne (2013), a new secondary phase [i.e., mosandrite-(Ce)] resulting from rinkite-(Ce) alteration was not observed in our samples. This may be explained by the relatively low water activity at the initial hydrothermal stage and the low degree of reactivity of rinkite-(Ce) to the alkali metasomatism (Andersen et al. 2013). ...
The nepheline syenite pegmatite in the Saima alkaline complex is characterized by local REE mineralization mainly occurring as rinkite-(Ce) and associated alteration minerals. As the most prominent REE-bearing mineral in the pegmatite, rinkite-(Ce) closely coexists with microcline, nepheline, natrolite and calcite. Some rinkite-(Ce) grains show compositional sector-zonation, in which inner core displays relatively high Ti, Ca, and Sr concentrations, but low Zr, REE, and Na contents. Primary rinkite-(Ce) has undergone multiple episodes of fluid interactions, and accordingly, from weak to strong, three different mineral assemblages of hydrothermal alteration can be summarized: (1) rinkite-(Ce) + secondary natrolite ± K-feldspar ± minor fluorbritholite-(Ce), (2) rinkite-(Ce) relics + secondary natrolite + K-feldspar + fluorbritholite-(Ce) + unidentified Ca-Ti silicate mineral + fluorite and calcite, and (3) pseudomorphs after rinkite-(Ce). The pseudomorph can be divided into two groups characterized by distinct mineral associations: (i) Ca-bearing strontianite + fluorbritholite-(Ce) + natrolite + fluorite + calcite coexisting with silicate minerals, and (ii) calcite + fluorite + fluorbritholite-(Ce) + rinkite-(Ce) relics ± Ca-bearing strontianite ± ancylite-(Ce) associated with calcite matrix. These alteration mineral assemblages probably suggest the magmatic-derived alkali-metasomatism associated with an alkali-CO2-F-rich fluid, and the Ca-metasomatism associated with another externally-derived Sr- and Ca-rich fluid. Metasomatic events act as the potential driven force for the rinkite-(Ce) dissolution and pseudomorph formation process. The high concentration of rinkite-(Ce) in the nepheline syenite pegmatite results from the fractional crystallization of the Saima CO2-rich alkaline silicate magma, and the successive alterations of rinkite-(Ce) attest of the important role played by hydrothermal fluids in controlling the remobilization of REE and the crystallization of 2 secondary rare earth minerals.
... Wöhlerite crystals in direct contact with saccharoidal albite are always altered into secondary zircon, pyrochlore and carbonate (Fig. 5B). Wöhlerite may also be altered around the rim with the association of fluorite and hiortdahlite (Andersen et al., 2013). ...
The Larvik Plutonic Complex (LPC) contains pegmatites with a wide array of mineral assemblages and morphological features. The pegmatites have traditionally been described as nepheline syenite and syenite pegmatites which carry agpaitic or miaskitic mineral assemblages, respectively. However, several pegmatites fall outside this simple characterisation due to 'agpaitic-like' late magmatic mineral assemblages such as hiortdahlite and eudialyte group minerals. Morphological and mineralogical differences between pegmatites are not unique to, or related with, specific areas of the LPC. Compositional variation and deformation features of the host pluton are the main mechanisms for differing morphology and mineral assemblages between LPC pegmatites. Natrolite replacement of feldspathoid is the most common alteration feature in the nepheline syenite pegmatites. The extent of alteration is closely associated with crystallisation of saccharoidal albite and aegirine. Detailed description of a nepheline syenite pegmatite situated in the Sagåsen quarry provides new insights into the internal evolution and mineral distribution of a large representative pegmatite body. The most important mechanism driving hydrous alteration is the crystallisation of anhydrous primary minerals which leads to an immiscible hydrous fluid driving in situ alterations of primary mineral assemblages.
... Reference compositions are from the Phlegrean Fields (Melluso et al. 2012), Ischia (Melluso et al. 2014),Gharyan (Lustrino et al. 2012),Itatiaia (Melluso et al. 2017), and Sushina Hill (Chakrabarty et al. 2018). The reference compositions of the Oslo Rift nepheline syenites are taken fromAndersen et al. (2010Andersen et al. ( , 2012a. The structural formulae were calculated assuming Si þ Al ¼ 8 cations per formula unit. ...
The Passa Quatro alkaline complex is one of the main intrusions in the Serra do Mar Cretaceous to Paleogene Igneous
Province of southeastern Brazil. It is composed mainly of nepheline syenites and alkali syenites, with minor phonolitic dikes.
The dominant felsic phases are potassic feldspar and nepheline, with minor sodic plagioclase in less silica-undersaturated rocks.
The main mafic phases are clinopyroxene, amphibole, biotite, and oxides. The wealth of accessory phases includes titanite,
eudialyte, astrophyllite–kupletskite, F-disilicates, phosphates, phosphosilicates, and F-REE-carbonates, with their specific
ranges of composition. These accessory minerals often mantle zircon and fluorite corroded crystals, evidence of (1) the
petrographic transition from miaskitic to agpaitic in the same rock, and (2) a decrease in the activity of fluorine in the coexisting
residual magmas, from the stability range of fluorite to that of F-poorer disilicates. There is also a major role, as yet
undervalued, for manganese in the phase stability of the various accessory phases in rocks/magmas devoid of magnesium. The
three neighboring complexes of Itatiaia, Passa Quatro, and Po¸cos de Caldas have significant differences in the types and
amounts of agpaitic minerals in their peralkaline rocks. The Passa Quatro intrusion (with aegirine, titanite, and minor eudialyte)
can be considered slightly more silica undersaturated and peralkaline than the nearby Itatiaia complex and has transitional
features towards the highly agpaitic nepheline syenites of Po¸cos de Caldas (with aegirine, titanite, eudialyte, and aenigmatite).
Eudialyte and titanite represent accessory phases that influence the incompatible element behavior in the residual magmatic
compositions (mostly phonolites and peralkaline phonolites) of the Serra do Mar potassic province.
... The pegmatite has been dated at 293.2(13) Ma (Dahlgren et al. 1998, Müller et al. 2017. The Tuften quarry is one of several actively used sources of larvikite (a local name for alkali syenite or monzonite) and is associated with the Permian-aged Larvik Plutonic Complex (LPC) of the southern part of the Oslo Graben (Petersen 1978, Pedersen et al. 1995, Andersen et al. 2013. The LPC is characterized by relatively large syenite and nepheline syenite pegmatites. ...
This paper presents the results of 57Fe Mössbauer spectroscopy, SEM-EDS analysis, gamma-ray spectrometry, and X-ray diffraction (XRD) patterns for an unknown metamict phase (UMP) from a syenite pegmatite at Tuften quarry, southern Norway. The sample exhibits²³²Th and²³⁸U activities of 137 and 2.6 Bq g⁻¹, respectively, and a calculated total absorbed a-dose of 83 1015 a-decay mg-1. Its chemical composition falls generally between chevkinite-(Ce)-perrierite-(Ce) and allanite-(Ce)- ferriallanite-(Ce) mineral compositions. The Mössbauer spectrum of an untreated UMP sample can be fitted to two Fe²⁺ and Fe³⁺ quadrupole doublets assigned to octahedral coordination with a relative Fe2+/RFe ratio of 0.11. A sample of the UMP was also annealed in argon for one hour at 1273 K. Powder of the completely recrystallized sample was subjected to XRD analysis and indexed to the P121 space group with unit-cell dimensions of a 8.179 A , b 14.16 A , c 4.291 A , and β = 96.718. The corresponding Mössbauer spectrum is characterized by the presence of three quadrupole doublets also assigned to Fe²⁺ and Fe³⁺ in octahedral coordination with a relative Fe²⁺/RFe ratio of 0.15. One of the Fe3+ doublets shows extremely high quadrupole splitting of 2.60 mm s⁻¹, implying extreme distortion of the coordination octahedra. © 2018 Mineralogical Association of Canada. All rights reserved.
... Table 8) and, consequently, they plot below the line joining the other phases, suggesting cationic vacancies with respect to the formula normalized to eight Si. These low totals have already been observed by Andersen et al. (2013). The compositional characteristics of these phases are best exemplified in the diagrams of Fig. 8 and Suppl. ...
... More generally, there is need of a more stringent chemical classification of these phases, in the absence (and usefulness) of crystallographic determinations made crystalby-crystal, composition-by-composition (e.g. Atencio et al., 1999;Christiansen et al., 2003a,b;Chakhmouradian et al., 2008;Andersen et al., 2013;Melluso et al., 2014b). (Fig. 9a,b,c). ...
... The F-disilicates of Itatiaia are commonly found in other syenites and peralkaline silicaundersaturated rocks worldwide (e.g. Platt, 1986, 1988;Moreau et al., 1996;Atencio et al., 1999;Carbonin et al., 2005;Ridolfi et al., 2006;Andersen et al., 2010Andersen et al., , 2013Lustrino et al., 2012;Melluso et al., 2012a;2014b;Rønsbo et al., 2014). They are the result of the concentration of the remaining fluorine (after fluorite crystallization and/ or fluorite resorption) and other elements in the interstitial liquids after the dominant crystallization of felsic phases, but the (apparently random) combination of different disilicates in a given rock, their widely changing Ca/Na, Mn/Fe, Ti/Zr and Zr/ Nb ratios, and the concentration of REE are still poorly understood from a thermodynamic point of view (Andersen et al., 2010). ...
The Late Cretaceous Itatiaia complex is made up of nepheline syenite grading to peralkaline varieties, quartz syenite and granite, emplaced in the metamorphic rocks of the Serra do Mar, SE Brazil. The nepheline syenites are characterized by assemblages with alkali feldspar, nepheline, Fe-Ti oxides, clinopyroxene, amphibole, apatite and titanite, while the peralkaline nepheline syenites have F-disilicates (rinkite, wöhlerite, hiortdahlite, låvenite), britholite and pyrophanite as the accessory phases. The silica-oversaturated rocks have alkali feldspar, plagioclase, quartz, amphibole, clinopyroxene and Fe-Ti oxides; the chevkinite-group minerals are the featured accessory phases and are found with allanite, fluorapatite, fluorite, zircon, thorite, yttrialite, zirconolite, pyrochlore and yttrocolumbite. The major- and trace-element composition of the Itatiaia rocks have variations linked to the amount of accessory phases, have smooth, enriched chondrite-normalized rare-earth element (REE) distribution patterns in the least-evolved nepheline syenites and convex patterns in the most-evolved nepheline syenites. The REE distribution patterns of the quartz syenites and granites show a typical pattern caused by fractional crystallization of feldspar and amphibole, in an environment characterized by relatively high oxygen fugacity (>NiNiO buffer) and high concentrations of H2O and F, supporting the crystallization of hydrous phases, fluorite and F-disilicates. The removal of small amounts of titanite in the transition from the least-evolved to the most-evolved nepheline syenites stems from petrogenetic models involving REE, and is shown to be a common feature of the magmatic evolution of many other syenitic/ trachytic/ phonolitic complexes of the Serra do Mar and elsewhere.
