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Study of the Eudialyte Group Minerals

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A special issue of Minerals (ISSN 2075-163X). This special issue belongs to the section "Crystallography and Physical Chemistry of Minerals & Nanominerals".

Deadline for manuscript submissions: closed (30 April 2021) | Viewed by 32947

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Special Issue Editors

Dr. Ramiza K. Rastsvetaeva

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Guest Editor

Federal Scientific Research Center "Crystallography and Photonics", Russian Academy of Sciences, 119991 Moscow, Russia
Interests: eudialyte group; silicate minerals; microporous materials; crystal structure; crystal chemistry of minerals

Dr. Sergey M. Aksenov

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Co-Guest Editor

Kola Science Center, Russian Academy of Sciences, 184209 Apatity, Russia
Interests: X-ray crystallography; inorganic crystal chemistry; crystallography of modular materials; topology of crystal structures; systematics and nomenclature of minerals and inorganic compounds
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Special Issue Information

Dear Colleagues,

It is our pleasure to announce a Special Issue of the journal Minerals on the topic of "The Study of Eudialyte-Group Minerals". Members of the eudialyte group, including 27 valid mineral species, are important components of some specific types of alkaline rocks which are known in many alkaline provinces. Due to selective features of some crystallographic sites, these minerals play an important role in petrology and geochemistry as indicators of mechanisms of rock-forming processes. A distinctive feature of the eudialyte-group minerals is the unique complexity and variability of their crystal structures. These minerals have proven to be a very effective model, based on which many crystal–chemical, geochemical, and genetic patterns have been established. Complex mechanisms of isomorphic substitutions involving numerous crystallographic sites put this group into the category of unique minerals in terms of the number of potential new species. Eudialyte-group minerals concentrate different important and strategic metals, including zirconium, hafnium, niobium, and rare-earth elements. This feature allows us to consider eudialyte-rich rocks as a prospective source of these elements. Thanks to the microporous character of the structure, which is based on a heteropolyhedral framework hosting different cations and anions, eudialyte-group minerals exhibit ion-exchange properties. However, the extraction of strategic elements from the eudialyte concentrate is rather challenging because of the structural and compositional complexity of the crystal structure of eudialyte and related minerals. This Special Issue is a good chance to summarize recent data on different aspects of the study of eudialyte-group minerals. We hope that this solid work will be an important contribution to the knowledge on the genesis, mineralogy, geochemistry, petrology, crystallography, spectroscopy, processing, and industrial importance of eudialyte-group minerals and will stimulate their further investigation.

Dr. Ramiza K. Rastsvetaeva
Dr. Sergey M. Aksenov
Guest Editors

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Keywords

eudialyte-group minerals
mineral species
isomorphic substitutions
ion-exchange properties
extraction of strategic elements

Published Papers (13 papers)

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Research

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16 pages, 3411 KiB

Open AccessArticle

Recovery of Uranium, Thorium, and Other Rare Metals from Eudialyte Concentrate by a Binary Extractant Based on 1,5-bis[2-(hydroxyethoxyphosphoryl)-4-ethylphenoxy]-3-oxapentane and Methyl Trioctylammonium Nitrate

by Alfiya M. Safiulina, Alexey V. Lizunov, Aleksandr A. Semenov, Dmitriy V. Baulin, Vladimir E. Baulin, Aslan Yu. Tsivadze, Sergey M. Aksenov and Ivan G. Tananaev

Minerals 2022, 12(11), 1469; https://doi.org/10.3390/min12111469 - 20 Nov 2022

Cited by 3 | Viewed by 1772

Abstract

Eudialyte-group minerals are of scientific interest as important concentrators of rare elements (mainly Zr and REE) in agpaitic alkaline rocks and a potential source of REE, Zr, Hf, Nb, and Ta for industrial use. Extraction of uranium(VI), thorium(IV), zirconium(IV), hafnium(IV), titanium(IV), and scandium(III) by a binary extractant based on 1,5-bis[2-(hydroxyethoxyphosphoryl)-4-ethylphenoxy]-3-oxapentane and methyl trioctylammonium nitrate from eudialyte breakdown solutions is studied. Extraction isotherms were obtained and exhaustive extraction was investigated. It is shown that uranium, thorium, hafnium, zirconium, scandium, and titanium are almost completely recovered in two-stage extraction by a mixture of 1,5-bis[2-(hydroxyethoxyphosphoryl)-4-ethylphenoxy]-3-oxapentane and methyltrioctylammonium nitrate in 1,2-dichloroethane. Quantitative characteristics were compared for uranium(VI), thorium(IV), zirconium(IV), hafnium(IV), titanium(IV), and scandium(III). It was shown that the extraction efficiency of the metals by the binary extractant based on 1,5-bis[2-(hydroxyethoxyphosphoryl)-4-ethylphenoxy]-3-oxapentane and methyltrioctylammonium nitrate in 1,2-dichloroethane is much higher in comparison with the commercially available tributyl phosphate. Full article

(This article belongs to the Special Issue Study of the Eudialyte Group Minerals)

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19 pages, 4489 KiB

Open AccessArticle

Dissolution of the Eudialyte-Group Minerals: Experimental Modeling of Natural Processes

by Julia A. Mikhailova, Yakov A. Pakhomovsky, Galina O. Kalashnikova and Sergey M. Aksenov

Minerals 2022, 12(11), 1460; https://doi.org/10.3390/min12111460 - 18 Nov 2022

Cited by 3 | Viewed by 1451

Abstract

Eudialyte-group minerals (EGMs) are typical accessory or rock-forming minerals of the Lovozero peralkaline massif (Kola Peninsula, Russia). The EGM grains in the rocks of the massif are often replaced by an association of various secondary minerals such as lovozerite and wöhlerite group minerals, as well as terskite, catapleiite, elpidite, gaidonnayite, vlasovite, zircon, and loparite-(Ce). However, EGMs in the Lovozero massif can be not only pseudomorphized, but also partially or completely dissolved. The partial dissolution of eudialyte grains was simulated in three series of experiments, and the results obtained were compared with natural samples. Observations in natural samples and experimental studies have shown that the partial dissolution of eudialyte-group minerals occurs in two stages: (1) loss of sodium and hydration; (2) loss of other cations not included in the zirconosilicate framework. This process proceeds most intensively in acidic hydrothermal solutions and may be responsible for the appearance of new mineral species in the eudialyte group. Full article

(This article belongs to the Special Issue Study of the Eudialyte Group Minerals)

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19 pages, 3988 KiB

Open AccessArticle

Chlorine-Deficient Analog of Taseqite from Odikhincha Massif (Russia): Genesis and Relation with Other Sr-Rich Eudialyte-Group Minerals

by Victor A. Zaitsev, Nikita V. Chukanov and Sergey M. Aksenov

Minerals 2022, 12(8), 1015; https://doi.org/10.3390/min12081015 - 12 Aug 2022

Cited by 1 | Viewed by 1455

Abstract

Eudialyte-group minerals are important accessory minerals of peralkaline rocks of nepheline-syenite massifs and alkaline–ultramafic complexes. Here, we report the complex study of a eudialyte-group mineral (EGM) from peralkaline pegmatite of the alkaline-ultrabasic Odikhincha massif (Polar Siberia). The chemical composition of the studied EGM is intermediate between those of taseqite and eudialyte, with small admixtures of other members of the eudialyte group. The crystals of EGMs were formed during the postmagmatic stage in the temperature range of 300–350 °C and partly replaced by late eudialite along cracks during the zeolite stage (~230 °C). The chemical compositions, structural features and mineral association of the studied EGM are similar to those of Sr-Nb-dominant EGM found in other nepheline-syenite massifs, such as Khibiny, Lovozero and Pilansberg. The EGM studied in this work is a Cl-deficient taseqite variety (“monochlore taseqite”), which differs from “dichlorotaseqite” (found only in the Ilimaussaq massif) by a lower amount of chlorine. Full article

(This article belongs to the Special Issue Study of the Eudialyte Group Minerals)

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16 pages, 2571 KiB

Open AccessEditor’s ChoiceArticle

Who Is Who in the Eudialyte Group: A New Algorithm for the Express Allocation of a Mineral Name Based on the Chemical Composition

by Julia A. Mikhailova, Dmitry G. Stepenshchikov, Andrey O. Kalashnikov and Sergey M. Aksenov

Minerals 2022, 12(2), 224; https://doi.org/10.3390/min12020224 - 9 Feb 2022

Cited by 6 | Viewed by 1854

Abstract

Eudialyte-group minerals (EGMs) are Na-Ca zirconosilicates typical for peralkaline plutonic rocks. In the zeolite-like crystal structure of these minerals, there are many sites of different volumes and configurations, and therefore EGMs can include up to one-third of the periodic table. Although there are preferred sites for many elements in the crystal structure of eudialyte-group minerals, the same element can appear in several sites. In addition, many sites may be partially or fully vacant. Currently, 30 mineral species are established in the eudialyte group. However, this diversity is, in fact, limited to holotype specimens. To name any mineral from the eudialyte group, you need to solve its crystal structure and compare it with holotypes. Meanwhile, the composition (and, therefore, the name) of any mineral of the eudialyte group is an excellent indicator of the composition of the mineral-forming media, which is very important to petrological and mineralogical studies. In this article, we propose a diagnostic scheme for minerals of the eudialyte group, based only on the chemical composition. The scheme includes five consecutive steps, each of which evaluates the content of a species-forming element (or the sum of such elements). This scheme can be supplemented by new members without changing its hierarchical structure. Full article

(This article belongs to the Special Issue Study of the Eudialyte Group Minerals)

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19 pages, 5118 KiB

Open AccessArticle

Zr-Rich Eudialyte from the Lovozero Peralkaline Massif, Kola Peninsula, Russia

by Taras L. Panikorovskii, Julia A. Mikhailova, Yakov A. Pakhomovsky, Ayya V. Bazai, Sergey M. Aksenov, Andrey O. Kalashnikov and Sergey V. Krivovichev

Minerals 2021, 11(9), 982; https://doi.org/10.3390/min11090982 - 9 Sep 2021

Cited by 3 | Viewed by 3219

Abstract

The Lovozero peralkaline massif (Kola Peninsula, Russia) has several deposits of Zr, Nb, Ta and rare earth elements (REE) associated with eudialyte-group minerals (EGM). Eudialyte from the Alluaiv Mt. often forms zonal grains with central parts enriched in Zr (more than 3 apfu) and marginal zones enriched in REEs. The detailed study of the chemical composition (294 microprobe analyses) of EGMs from the drill cores of the Mt. Alluaiv-Mt. Kedykvyrpakhk deposits reveal more than 70% Zr-enriched samples. Single-crystal X-ray diffraction (XRD) was performed separately for the Zr-rich (4.17 Zr apfu) core and the REE-rich (0.54 REE apfu) marginal zone. It was found that extra Zr incorporates into the octahedral M1A site, where it replaces Ca, leading to the symmetry lowering from R

\bar{3}

m to R32. We demonstrated that the incorporation of extra Zr into EGMs makes the calculation of the eudialyte formula on the basis of Si + Al + Zr + Ti + Hf + Nb + Ta + W = 29 apfu inappropriate. Full article

(This article belongs to the Special Issue Study of the Eudialyte Group Minerals)

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14 pages, 4639 KiB

Open AccessArticle

Compositional Variation of Eudialyte-Group Minerals from the Lovozero and Ilímaussaq Complexes and on the Origin of Peralkaline Systems

by Lia N. Kogarko and Troels F. D. Nielsen

Minerals 2021, 11(6), 548; https://doi.org/10.3390/min11060548 - 21 May 2021

Cited by 5 | Viewed by 2002

Abstract

The Lovozero complex, Kola peninsula, Russia and the Ilímaussaq complex in Southwest Greenland are the largest known layered peralkaline intrusive complexes. Both host world-class deposits rich in REE and other high-tech elements. Both complexes expose spectacular layering with horizons rich in eudialyte group minerals (EGM). We present a detailed study of the composition and cryptic variations in cumulus EGM from Lovozero and a comparison with EGM from Ilímaussaq to further our understanding of peralkaline magma chambers processes. The geochemical signatures of Lovozero and Ilímaussaq EGM are distinct. In Lovozero EGMs are clearly enriched in Na + K, Mn, Ti, Sr and poorer Fe compared to EGM from Ilímaussaq, whereas the contents of ΣREE + Y and Cl are comparable. Ilímaussaq EGMs are depleted in Sr and Eu, which points to plagioclase fractionation and an olivine basaltic parent. The absence of negative Sr and Eu anomalies suggest a melanephelinitic parent for Lovozero. In Lovozero the cumulus EGMs shows decrease in Fe/Mn, Ti, Nb, Sr, Ba and all HREE up the magmatic layering, while REE + Y and Cl contents increase. In Lovozero EGM spectra show only a weak enrichment in LREE relative to HREE. The data demonstrates a systematic stratigraphic variation in major and trace elements compositions of liquidus EGM in the Eudialyte Complex, the latest and uppermost part of Lovozero. The distribution of elements follows a broadly linear trend. Despite intersample variations, the absence of abrupt changes in the trends suggests continuous crystallization and accumulation in the magma chamber. The crystallization was controlled by elemental distribution between EGM and coexisting melt during gravitational accumulation of crystals and/or mushes in a closed system. A different pattern is noted in the Ilimaussaq Complex. The elemental trends have variable steepness up the magmatic succession especially in the uppermost zones of the Complex. The differences between the two complexes are suggested to be related dynamics of the crystallization and accumulation processes in the magma chambers, such as arrival of new liquidus phases and redistributions by mush melts. Full article

(This article belongs to the Special Issue Study of the Eudialyte Group Minerals)

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27 pages, 6269 KiB

Open AccessArticle

Eudialyte Group Minerals from the Lovozero Alkaline Massif, Russia: Occurrence, Chemical Composition, and Petrogenetic Significance

by Julia A. Mikhailova, Yakov A. Pakhomovsky, Taras L. Panikorovskii, Ayya V. Bazai and Victor N. Yakovenchuk

Minerals 2020, 10(12), 1070; https://doi.org/10.3390/min10121070 - 29 Nov 2020

Cited by 8 | Viewed by 2584

Abstract

The Lovozero Alkaline Massif intruded through the Archean granite-gneiss and Devonian volcaniclastic rocks ca. 360 Ma ago and formed a large laccolith-type body. The lower part of the massif (the Layered complex) is composed of regularly repeating rhythms: melanocratic nepheline syenite (lujavrite, at the top), leucocratic nepheline syenite (foyaite), foidolite (urtite). The upper part of the massif (the Eudialyte complex) is indistinctly layered, and lujavrite enriched with eudialyte-group minerals (EGM) prevails there. In this article, we present the results of a study of the chemical composition and petrography of more than 400 samples of the EGM from the main types of rock of the Lovozero massif. In all types of rock, the EGM form at the late magmatic stage later than alkaline clinopyroxenes and amphiboles or simultaneously with it. When the crystallization of pyroxenes and EGM is simultaneous, the content of ferrous iron in the EGM composition increases. The Mn/Fe ratio in the EGM increases during fractional crystallization from lujavrite to foyaite and urtite. The same process leads to an increase in the modal content of EGM in the foyaite of the Layered complex and to the appearance of primary minerals of the lovozerite group in the foyaite of the Eudialyte complex. Full article

(This article belongs to the Special Issue Study of the Eudialyte Group Minerals)

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16 pages, 3052 KiB

Open AccessArticle

Odikhinchaite, Na₉Sr₃[(H₂O)₂Na]Ca₆Mn₃Zr₃NbSi (Si₂₄O₇₂)O(OH)₃(CO₃)·H₂O, a New Eudialyte-Group Mineral from the Odikhincha Intrusion, Taimyr Peninsula, Russia

by Yuliya D. Gritsenko, Nikita V. Chukanov, Sergey M. Aksenov, Igor V. Pekov, Dmitry A. Varlamov, Leonid A. Pautov, Svetlana A. Vozchikova, Dmitry A. Ksenofontov and Sergey N. Britvin

Minerals 2020, 10(12), 1062; https://doi.org/10.3390/min10121062 - 27 Nov 2020

Cited by 6 | Viewed by 2316

Abstract

The new eudialyte-group mineral, odikhinchaite, was discovered in a peralkaline pegmatite vein hosted by melteigite at the Odikhincha ultrabasic alkaline–carbonatite intrusion, Taimyr Peninsula, Krasnoyarsk Krai, Russia. Associated minerals are orthoclase, albite, aegirine, cancrinite, ancylite-(Ce), catapleiite, and wadeite. Odikhinchaite occurs as dense rosette-like aggregates up to 11 mm across, consisting of split lamellar individuals. The mineral is translucent to transparent, deep purple, with vitreous luster. Odikhinchaite is brittle, with uneven fracture; distinct cleavage on (001) is observed. Hardness determined by the micro-indentation method is equal to 430 kgf/mm²; the Mohs hardness is 5. D(meas.) is 2.97(1) g·cm⁻³, D(calc.) is 3.04 g·cm^–3. Odikhinchaite is optically uniaxial (–), ω = 1.638(2), ε = 1.630(2). The IR spectrum shows the presence of the ^IVMn²⁺O₄ polyhedra, H₂O molecules and CO₃^2– anions. The chemical composition is (electron microprobe, H₂O determined by the modified Penfield method, CO₂ determined by selection sorption of gaseous annealing products; wt%): Na₂O 9.25, K₂O 0.59, CaO 12.77, MnO 5.49, FeO 0.75, MgO 0.24, La₂O₃ 0.38, Ce₂O₃ 0.39, Nd₂O₃ 0.15, Al₂O₃ 0.07, SiO₂ 44.80, ZrO₂ 11.13, TiO₂ 0.07, Nb₂O₅ 4.17, Cl 0.69, CO₂ 0.90, H₂O 2.22, –O = Cl –0.16, total 99.72. The crystal structure was solved using single-crystal X-ray diffraction data. Odikhinchaite is trigonal, space group R3m; the unit-cell parameters are: a = 14.2837(2) Å, c = 30.0697(3) Å, V = 5313.04(12) Å³. The new mineral is isostructural with other 12-layered members of the eudialyte group with the space group R3m. Its crystal chemical formula is (Z = 3): {^N¹(Na_2.58Ca_0.42)^N²[Na_2.37Ca_0.51(H₂O)_0.12]^N³(Sr_2.00K_0.45Na_0.35REE_0.20)^N⁴Na₃^N⁵[(H₂O)_1.8Na_1.2]}{^ZZr₃^M¹Ca₆^M²(Mn_2.49Fe²⁺_0.51)[^M³Nb(OH)_1.82O_1.18](^M⁴SiOH)[Si₃O₉]₂[Si₉O₂₇]₂^X¹[(CO₃)_0.53Cl_0.47]^X²[(H₂O)_0.6(O,F)_0.4]^XM⁴(CO₃)_0.15. The strongest lines of the powder X-ray diffraction pattern [d, Å (I, %) (hkl)] are: 11.42 (64) (101), 4.309 (41) (205), 3.405 (53) (131), 3.208 (45) (208, 036), 3.167 (44) (217), 2.978 (100) (315), 2.858 (86) (404). Full article

(This article belongs to the Special Issue Study of the Eudialyte Group Minerals)

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18 pages, 3339 KiB

Open AccessArticle

Chemical Composition and Petrogenetic Implications of Eudialyte-Group Mineral in the Peralkaline Lovozero Complex, Kola Peninsula, Russia

by Lia Kogarko and Troels F. D. Nielsen

Minerals 2020, 10(11), 1036; https://doi.org/10.3390/min10111036 - 20 Nov 2020

Cited by 12 | Viewed by 3795

Abstract

Lovozero complex, the world’s largest layered peralkaline intrusive complex hosts gigantic deposits of Zr-, Hf-, Nb-, LREE-, and HREE-rich Eudialyte Group of Mineral (EGM). The petrographic relations of EGM change with time and advancing crystallization up from Phase II (differentiated complex) to Phase III (eudialyte complex). EGM is anhedral interstitial in all of Phase II which indicates that EGM nucleated late relative to the main rock-forming and liquidus minerals of Phase II. Saturation in remaining bulk melt with components needed for nucleation of EGM was reached after the crystallization about 85 vol. % of the intrusion. Early euhedral and idiomorphic EGM of Phase III crystalized in a large convective volume of melt together with other liquidus minerals and was affected by layering processes and formation of EGM ore. Consequently, a prerequisite for the formation of the ore deposit is saturation of the alkaline bulk magma with EGM. It follows that the potential for EGM ores in Lovozero is restricted to the parts of the complex that hosts cumulus EGM. Phase II with only anhedral and interstitial EGM is not promising for this type of ore. Nor is the neighboring Khibiny complex despite a bulk content of 531 ppm of Zr. Khibiny only has interstitial and anhedral EGM. The evolution of the Lovozero magma is recorded in the compositions EGM up through a stratigraphy of 2400 m in Phase II and III of the complex, and distinct in elements like rare earth elements (REE), Sr, Ba, Th, U, Rb, Mn, Fe. The compositional evolution reflects primarily fractional crystallization processes within the magma chamber itself in combination with convective magma flow and layering by precipitation of minerals with different settling velocities. The suggested mechanism for the formation of the EGM deposits is flotation of very small, suspended EGM crystals in the convective magma and concentration below the roof of the magma chamber. Phase III EGM is enriched in total REE (1.3%) and in HREE (Ce/Yt = 8.8) and constitutes a world class deposit of REE in the million tons of Phase III eudialyte lujavrites. Full article

(This article belongs to the Special Issue Study of the Eudialyte Group Minerals)

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23 pages, 3524 KiB

Open AccessArticle

Changes in Halogen (F, Cl, Br, and I) and S Ratios in Rock-Forming Minerals as Monitors for Magmatic Differentiation, Volatile-Loss, and Hydrothermal Overprint: The Case for Peralkaline Systems

by Hans G.M. Eggenkamp, Michael A.W. Marks, Petya Atanasova, Thomas Wenzel and Gregor Markl

Minerals 2020, 10(11), 995; https://doi.org/10.3390/min10110995 - 10 Nov 2020

Cited by 8 | Viewed by 2725

Abstract

We determined the halogen (F, Cl, Br, and I) and sulfur (S) concentrations in Cl-rich rock-forming minerals from five peralkaline complexes. We investigated sodalite (N = 42), eudialyte-group minerals (N = 84), and tugtupite (N = 8) from representative rock samples derived from Ilímaussaq (South Greenland), Norra Kärr (Sweden), Tamazeght (Morocco), Lovozero, and Khibina (Russian Federation). Taken together, sodalite and eudialyte-group minerals dominate the Cl and Br budget of the investigated rocks. For F, however, several other phases (e.g., amphibole, fluorite, villiaumite, and minerals of the rinkite group and the apatite supergroup) are additional sinks, and parts of the S may be scavenged in generally rare sulfides. The investigated minerals contain Cl at the wt.% level, F and S concentrations are in the hundreds to thousands of µg/g-range, Br is less common (0.2–200 µg/g) and I is rare (mostly well below 1 µg/g). Normalized to Cl, sodalite prefers Br relative to eudialyte-group minerals, while F is always enriched in the latter. Our data show that both F and S may represent important components in eudialyte-group minerals, sometimes at similar levels as Cl, which normally dominates. Sulfur reveals redox-dependent behavior: Under reduced crystallization conditions, S is more compatible in eudialyte-group minerals (EGM) than in sodalite, which flips to the opposite under water-rich and presumably more oxidized conditions. We investigate the applicability of F/Cl, Br/Cl, and S/Cl ratios in these minerals in peralkaline systems to better understand the interplay of magmatic differentiation, fluid loss and hydrothermal overprint. Similar to apatite in metaluminous systems, fractionation of sodalite, and eudialyte-group minerals in peralkaline magmas leads to decreasing Br/Cl ratios. The data presented in this study bear implications for the mineral chemistry and compositional variation of sodalite and especially EGM in general. Volatile components in EGM that are not normally considered, such as F and S, can reach concentrations of thousands of µg/g. Especially in the case of F, with its low atomic weight, the results obtained in this study indicate that it is very significant for formulae calculations, neutral charge-balance, and similar aspects at such concentration levels. This study demonstrates that halogen contents and ratios are sensitive monitors for a variety of processes in magmatic-hydrothermal systems, including magmatic fractionation, volatile loss, and fluid–rock interaction. Full article

(This article belongs to the Special Issue Study of the Eudialyte Group Minerals)

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16 pages, 5987 KiB

Open AccessArticle

New Data on the Isomorphism in Eudialyte-Group Minerals. 1. Crystal Chemistry of Eudialyte-Group Members with Na Incorporated into the Framework as a Marker of Hyperagpaitic Conditions

by Ramiza K. Rastsvetaeva, Nikita V. Chukanov, Igor V. Pekov, Christof Schäfer and Konstantin V. Van

Minerals 2020, 10(7), 587; https://doi.org/10.3390/min10070587 - 29 Jun 2020

Cited by 21 | Viewed by 2435

Abstract

A review of the crystal chemistry of Fe-deficient eudialyte-group minerals is given. Specific features of cation distribution over key sites in the crystal structure, including partial substitution of Fe²⁺ with Na, Mn and Zr at the M2 site are discussed. It is concluded that Na-dominant (at the M2 site) eudialyte-group members (^M²Na-EGMs) are markers of specific kinds of specific peralkaline (hyperagpaitic) igneous rocks and pegmatites. New data are obtained on the chemical composition, IR spectra and crystal chemistry for two samples of ^M²Na-EGMs with disordered M1 cations, which are a potentially new mineral species with the simplified formula (Na,H₂O)₁₅Ca₆Zr₃[Na₂(Fe,Zr)][Si₂₆O₇₂](OH)₂Cl·nH₂O. Full article

(This article belongs to the Special Issue Study of the Eudialyte Group Minerals)

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Review

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18 pages, 4051 KiB

Open AccessReview

Review on the Compositional Variation of Eudialyte-Group Minerals in the Ilímaussaq Complex (South Greenland)

by Michael A.W. Marks, Hans G.M. Eggenkamp, Petya Atanasova, Felicitas Mundel, Sascha Kümmel, Matthias Hagen, Thomas Wenzel and Gregor Markl

Minerals 2020, 10(11), 1011; https://doi.org/10.3390/min10111011 - 13 Nov 2020

Cited by 7 | Viewed by 2310

Abstract

We review the compositional variation of eudialyte-group minerals (EGM) from the Ilímaussaq complex in South Greenland. Investigated samples cover all major rock units and associated pegmatites and aplites. The whole data set (>3000 analyses from >250 samples) exhibits variable XMn (0.1–0.5), REE (0.2–1.7 apfu), Nb (0.1–0.4), and Cl contents (0.4–1.6 apfu). Most EGM compositions are Na-rich (13–15 apfu), while deviations to Na-rich but also to Na-poor compositions occur because of a combination of primary features (peralkalinity, water activity) and secondary alteration. During magma evolution, REE contents in EGM cores generally increase and reach their highest contents in the most evolved rock units of the complex. This points to the moderate compatibility of REE in EGM and a bulk D (cEGM/cmelt) value of <1 during magma differentiation. Chlorine contents in EGM cores continuously decrease, and are lowest at the rims of individual crystals, suggesting a continuous decrease of Cl activity in the magmas by large-scale EGM and sodalite extraction during the orthomagmatic stage and water enrichment during the late-magmatic stage. The overall variations of XMn across stratigraphy are only minor and likely influenced by the co-crystallization of sodic pyroxene and amphibole (c.f. aegirine, arfvedsonite) and local phase proportions. Similarly, Nb and Ti contents are influenced by co-crystallizing aenigmatite, rinkite, and others. Their presence buffers Ti and Nb contents to rather constant and low values, while their absence may cause variable enrichment on a local scale. Very low Sr contents (<0.1 apfu) in magmatic EGM from Ilímaussaq are related to the basaltic nature of the parental magmas of the complex, as large-scale plagioclase fractionation occurred prior to the formation of the Ilímaussaq magmas, effectively removing Sr from the system. This is in line with very strong negative Eu anomalies in EGM from Ilímaussaq. Consistently, Sr contents in EGM from alkaline complexes, for which foiditic parental magmas are assumed, are much higher and, in such cases, negative Eu anomalies are generally absent. Full article

(This article belongs to the Special Issue Study of the Eudialyte Group Minerals)

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New Data on the Isomorphism in Eudialyte-Group Minerals. 2. Crystal-Chemical Mechanisms of Blocky Isomorphism at the Key Sites

by Ramiza K. Rastsvetaeva and Nikita V. Chukanov

Minerals 2020, 10(8), 720; https://doi.org/10.3390/min10080720 - 17 Aug 2020

Cited by 21 | Viewed by 4027

Abstract

The review considers various complex mechanisms of isomorphism in the eudialyte-group minerals, involving both key positions of the heteropolyhedral framework and extra-framework components. In most cases, so-called blocky isomorphism is realized when one group of atoms and ions is replaced by another one, which is accompanied by a change in the valence state and/or coordination numbers of cations. The uniqueness of these minerals lies in the fact that they exhibit ability to blocky isomorphism at several sites of high-force-strength cations belonging to the framework and at numerous sites of extra-framework cations and anions. Full article

(This article belongs to the Special Issue Study of the Eudialyte Group Minerals)

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