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Articles |
i Balic-
unic2
1 Institut des Matériaux Jean Rouxel, UMR 6502 CNRS-Université de Nantes, 2, rue de la Houssinière, 44 322 Nantes Cedex 3, France
2 Department of Geography and Geology, University of Copenhagen, Østervoldgade 10, 1350 Copenhagen, Denmark
3 IGEM, Russian Academy of Sciences, Staromonetny per. 35, Moscow 109017, Russia
4 Leslie Research and Consulting, 316 Rosehill Wynd, Tsawwassen, B.C. V4M 3L9, Canada
5 Natural History Museum (Geology), University of Oslo, Postboks 1172 Blindern, 0318 Oslo, Norway
6 South Australian Museum, Department of Mineralogy, North Terrace, Adelaide, South Australia 5000, Australia
7 Department of Materials Engineering and Physics, University of Salzburg, Hellbrunnerstraße 34, 5020 Salzburg, Austria
8 CSIRO-Exploration & Mining, PO Box 5, Wembley, Western Australia 6913, Australia
9 Naturhistorisches Museum, Augustinerstraße 2, 4001 Basel, Switzerland
10 Institute of Mineral Industry, Danish Technical University, 2800 Lyngby, Denmark
11 Dipartimento Geomineralogico, Università degli Studi di Bari, via E. Orabona 4, 70125 Bari, Italy
12 Museo di Storia Naturale, Sezione di Mineralogia, Università degli Studi di Firenze, via La Pira 4, 50121 Firenze, Italy
13 Institute of Mineralogy, Crystallography and Material Science, University of Leipzig, Scharnhorststraße 20, 04275 Leipzig, Germany
14 Department of Earth Sciences, Faculty of Sciences, University of Toyama, Toyama 9308555, Japan
* Corresponding author, e-mail: Yves.Moelo{at}cnrs-imn.fr
** Corresponding author, e-mail: emilm{at}ged.ku.dk
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Abstract |
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 Top Abstract PreamblePart I. Revision of...Part II. Review of...3. Lead sulfosalts based...4. Sulfosalts based on...5. Specific Tl(Pb) and...6. Sulfosalts with an...7. Unclassified sulfosalts8. ConclusionAppendix: Additional list of...References |
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Key-words: sulfosalt, nomenclature, crystal chemistry, systematics.
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Preamble |
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TopAbstractPreamblePart I. Revision of...Part II. Review of...3. Lead sulfosalts based...4. Sulfosalts based on...5. Specific Tl(Pb) and...6. Sulfosalts with an...7. Unclassified sulfosalts8. ConclusionAppendix: Additional list of...References |
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The International Mineralogical Association (IMA) was founded in 1958. To coordinate its regular activity between general meetings (held every two years initially, and every four years since 1982), the IMA organized different specialized commissions, the best known being the Commission on New Minerals and Mineral Names (CNMMN – now Commission on New Minerals, Nomenclature and Classification, CNMNC). The Commission on Ore Microscopy (COM), since renamed the Commission on Ore Mineralogy, was originally created to establish quantitative data on the optical properties of opaque minerals. The data were subsequently published as Quantitative Data File volumes (see the Web-site of the IMA-COM). Within this Commission, the aim of the Sulfosalt Sub-Committee, under the direction of late Dr Roy Phillips, Chairman, was primarily to collect data for a complex group of ore minerals which, at the time, were poorly characterised. During the 13th General Meeting of IMA at Varna, Bulgaria (1982), Dr N. Mozgova succeeded R. Phillips as the new chair, with Dr. Y. Moëlo as secretary and the active collaboration of D.C. Harris (CANMET, Ottawa). Since the 15th IMA meeting at Beijing, China (1990), the activity of the Sulfosalt Sub-Committee has been carried on by us (Moëlo & Makovicky), primarily by compiling the internal reports and disseminating these among the committee members and specialists.
During the last four decades there has been a tremendous evolution of knowledge in the field of mineral systematics. More than 60 % of the mineral species known today were described since the foundation of the IMA-CNMMN. The percentage is even higher in the field of ore minerals, especially the complex groups of sulfosalts and the minerals of the platinum-group elements (Cabri, 1981, 2002). Together with the classic procedures to define the ore minerals, the increasing number of crystal-structure studies has permitted a general deciphering of the crystal chemistry of sulfosalts, which is the basis for a precise definition of mineral species and an understanding of their limits of validity.
This report is an update of the systematics of sulfosalts, reflecting a fruitful collaboration, past and present, of many specialists of sulfosalt mineralogy. Part I presents generalities concerning the definition and chemistry of sulfosalts, as well as some basic principles relevant to sulfosalt crystal-chemical classification. Part II is a detailed presentation of all known sulfosalts species, with selected references about their definition (if recent) and crystal structure (if solved). Problems concerning the definition and nomenclature of some species are discussed on the basis of published data.
The choice of the crystal-chemical scheme used for the classification in Part II is a development of the modular approach to crystal structures. This choice does not necessarily reflect that of all the contributors and committee members, who may have adopted other points of view; above all, the choice is intended to promote the use of crystal-structure analysis as a basis for understanding the complex chemistry of sulfosalts in nature.
A draft version of this report was presented by E. Makovicky during the 19th General Meeting of the IMA at Kobe, Japan (July 23–28, 2006). A copy of this internal report was sent to the national representatives of the COM and CNMNC, for information and critical reading. This circulation led to significant improvements in the preparation of the final manuscript. The report has been approved as a whole by the CNMNC, through the direction of its Secretary, W.D. Birch. Nevertheless, due to the complexity of the sulfosalt group, this final version may contain errors and imperfections, for which we (Y.M. & E.M.) accept sole responsibility. Above all, this report must be considered as a guide for specialists interested in the field of ore mineralogy, and as help for the discovery and description of new mineral species. Without any excessive pretention, we hope that the report will be considered as the "state of the art" in sulfosalt systematics; however, the details of the classification of these species are considered as a basis for further work rather than a definitive scheme. The review of sulfosalt systematics may also be useful in the field of solid-state chemistry and material sciences, as sulfosalts today have aroused increasing attention in the search for new materials with interesting physical properties, such as in thermoelectricity, photovoltaic conversions, and magnetism.
All participating members are sincerely thanked for their contribution. We mention especially Dr N. Mozgova, past President of the Sulfosalt Sub-Committee, as well as Drs J.L. Jambor, N. Cook (Chairman of the IMA-COM) and E.H. Nickel (former Vice-Chairman of the CNMMN), for their careful reading of the text. We also thank E.A.J. Burke and W.D. Birch (Chairman and Secretary of the CNMNC, respectively), and anonymous members of this commission, as well as Prof. Y. Takéuchi (University of Tokyo) and Dr. Y. Matsushita (National Institute for Materials Science), for their useful comments and corrections.
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Part I. Revision of sulfosalt definition and nomenclature: generalities |
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TopAbstractPreamblePart I. Revision of...Part II. Review of...3. Lead sulfosalts based...4. Sulfosalts based on...5. Specific Tl(Pb) and...6. Sulfosalts with an...7. Unclassified sulfosalts8. ConclusionAppendix: Additional list of...References |
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1. Definition and general formula
1.1. What is a sulfosalt?
The term "sulfosalt" (or "thiosalt") was created by chemists during the XIXth century, by analogy to complex salts of oxygen, such as sulfate, phosphate, arsenate, antimonate, arsenite and antimonite. Oxysalts generally correspond to the combination of a simple cation with a complex anion (MeOm)n–; this has been confirmed by crystal-structure studies and bond-valence calculations. In sulfosalts, S is considered to play the role of oxygen to similarly form complex anions. Although the configurations found in most modern studies of sulfosalts are more complicated than those encountered in similar oxysalts (e.g., oxyarsenites), the term "sulfosalt" has been preserved as a practical, working category in the field of ore mineralogy. The main reason is that sulfosalt minerals form a genetically well-defined group encountered in specific conditions of ore formation, usually referred to as hydrothermal processes.
1.2. Chemical nomenclature: an extended definition
In the literature, the definition of sulfosalts takes either formal chemistry or structural considerations as the starting point. According to the chemical definition, most sulfosalts are thioarsenites, thioantimonites, thiobismuthites and their combinations, i.e., sulfosalts in which As, Sb and Bi have the same oxidation state +3. Goldfieldite is the only natural example of a thiotellurite (i.e., with Te4+).
Remark: In the chemical literature, elements of group 15 of the periodic system, P, As, Sb and Bi (but not N, chemically very different) are designated as "pnictogens" (like "chalcogens" for S, Se and Te). Compounds in which pnictogens act as anions correspond to pnictides (see "sulfosalt-pnictides" below).
If the bond-valence concept is accepted as a basis for classification, the sulfosalts of both the lower- or higher valence elements [with groups such as (As3+S3)3– or (As5+S4)3–] represent classification categories equally well justified as those of oxyarsenites (As3+O3)3– or oxyarsenates (As5+O4)3–. This aspect was first considered by Nowacki (1968, 1969). Any problem encountered for some sulfosalts using this concept will have a near-mirror image in the oxy-realm as well, with somewhat diminished covalence.
A very limited number of natural sulfosalts correspond to thioarsenates (As5+ – enargite, luzonite) or thioantimonates (Sb5+ – famatinite). There are about 15 thiostannates (Sn4+), mainly related to the ZnS archetypes (sphalerite and wurtzite), and a few thiogermanates (Ge4+). Similarly, sulvanite could be considered as a thiovanadate (V4+), whereas thio tungstates (W6+), and thio molybdates (Mo6+) are exceptional. Thiophosphates (P5+) are as yet unknown in nature. Minerals corresponding to selenio- and telluro-salts, with trivalent As, Sb or Bi, or, exceptionally, Sb5+ (permingeatite) are uncommon.
Table 1 enumerates these different types of chalcogeno-salts. The present report deals only with the definition and nomenclature of chalcogeno-salts with As3+, Sb3+, Bi3+ and Te4+, having lone-pair electrons with generally a strong stereochemical activity, that enhances the complexity of crystal structures. However, Table 2 summarizes all mineral species corresponding to other chemical types of chalcogeno-salts.
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In cylindrite and related compounds (its homeotype lévyclaudite and its homologue franckeite), the composite crystal structure is built on the regular alternation of two types of layers (Makovicky, 1976; Evain et al., 2006a), one pseudo-tetragonal ("Q" type), probably containing the bulk of Sb3+ or Bi3+, the other pseudo-hexagonal ("H" type), containing principally Sn4+. This series is thus of the thioantimonite/stannate type.
In schlemaite, (Cu,
)6(Pb,Bi)Se4 ( = vacancy), a crystal-structure study (Förster et al., 2003) gave the general formula (Cu6–xx)(Pb1–xBix)Se4 (with x close to 0.4), with identical coordinates for Pb and Bi. This species ought to be considered as a Bi-rich selenide of Pb, whereas the Bi-dominant derivative (x > 0.5), if it exists, would be a selenio-salt.
1.3. General formula of the principal sulfosalt category with As3+, Sb3+, Bi3+ or Te4+
1.3.1. Basic structural formula
As the bulk of natural thioarsenites, thiostannates, etc. corresponds structurally to homeotypes of simple sulfides, the term "sulfosalt" is usually limited to the vast group of chalcogeno-salts containing trivalent As, Sb or Bi, as well as (exceptionally) Te4+. They correspond to complex sulfides (more generally chalcogenides) wherein one or more of the cations As3+, Sb3+, Bi3+ or Te4+ is associated with one or more metallic cation(s), Me, as essential (intrinsic) constituents. The S2– anion may be replaced by Se2– or Te2– (chalcogeno-salts). Thus, the general chemical formula can be given as:
 | (1) |
From a structural point of view, atoms of the metals and atoms of the metalloids are not bonded to one another, and are bonded only to anions. Thus, compounds such as arsenopyrite, FeAsS, löllingite, FeAs2, or gudmundite, FeSbS, are not sulfosalts, as As or Sb are directly bonded to Fe, and act as anions relative to the metal. In sulfosalts, it is the lone-electron-pair activity of As3+, etc. and, as a consequence, a nearly universally present asymmetric coordination of these metalloids, that causes the structural complexity and specificity of these compounds, setting them apart from nearly all other chalcogenides.
1.3.2. Borderline compounds
Several mineral species combine the structural properties of sulfides (chalcogenides) with those of the other chemical groups, and can be considered as borderline cases.
Sulfur-excess compounds
Sulfur (chalcogen) excess corresponds to S–S bonds in the crystal structure. These occur alongside the metal–sulfur bonds. Such compounds may be qualified as "persulfides" ("perchalcogenides" – the words "polysulfides" and "polychalcogenides" are also convenient). A well-known example among sulfosalts is livingstonite, HgSb4S6(S2) (Srikrishnan & Nowacki, 1975). It is also the case for moëloite, Pb6Sb6S14(S3) (Orlandi et al., 2002), and of the synthetic sulfosalts Cu4Bi4X9 (X = S, Se – Bente & Kupik, 1984; Makovicky et al., 2002). Another possible example is that of museumite, Pb2(Pb, Sb)2S8[Te, Au]2 (Bindi & Cipriani, 2004a).
Subsulfides/subchalcogenides
In this case, the compounds have a sulfur (chalcogen) deficiency relative to those with ‘normal’ valences. Cations in their crystal structure show metal–metal or metalloid–metalloid bonding alongside the metal–chalcogen bonding. The name of "subsulfides" ("subchalcogenides") has been used for such cases.
As the first example, within the tetradymite homologous series of layered structures, all compounds having a chalcogen deficit display pairs of Bi atomic layers, implying Bi–Bi bonding. Such is the case for the thiobismutite babkinite, Pb2Bi2(S, Se)3.
In gabrielite, Cu2AgTl2As3S7, the valence balance is respected. Nevertheless, examination of the crystal structure (Bali
-uni et al., 2006) showed that Tl atoms form Tl–Tl pairs with a short distance (3.09 Å) corresponding to the sum of covalent radii, that indicates a metal–metal interaction. This is similar to the interaction in the Hg–Hg pairs (2.535 Å) in deanesmithite, (Hg2)Hg3CrO5S2 (Szymañski & Groat, 1997). In stalderite, Cu(Zn, Fe, Hg)2TlAs2S6 (Graeser et al., 1995), and its isotype routhierite, CuHg2TlAs2S6, Tl–Tl pairs, with a somewhat longer bond, are also present.
Dervillite, Ag2AsS2, vaughanite, HgTlSb4S7, and fettelite, Ag24HgAs5S20, all with unknown crystal structures, apparently have a small excess of positive charges with respect to the charge balance, thus probably indicating some cation–cation bonding. The "excess" of positive charges is more pronounced in criddleite, Ag2Au3TlSb10S10, and tvalchrelidzeite, Hg3SbAsS3 (Yang et al., accept.). In all of these structures either metalloid–metalloid or metal–metalloid bonds are probably present, or even entire antimonide portions exist. Analogies to these situations are pääkkonenite Sb2AsS2 (Bonazzi et al., 1995) and chalcothallite (a sulfide–antimonide of Tl and Cu) (Makovicky et al., 1980).
The same situation is encountered in two PGE (Platinum Group Elements)-bearing chalcogenides, borovskite, Pd3SbTe4, and crerarite, (Pt,Pb)Bi3(S, Se)4–x, for which the valence state of the metalloid is unknown.
Sulfosalt-pnictides
In the crystal structure of hauchecornite, Ni9Bi(Bi, Sb)S8, the pure Bi atom position is preferentially bound to four S atoms (together with two Ni atoms) and acts partly as a cation, whereas the mixed (Bi, Sb) atom is exclusively bound to Ni atoms, and acts as an anion (Kocman & Nuffield, 1974). The same duality can be observed in other species isotypic with hauchecornite: arsenohauchecornite, bismutohauchecornite, tellurohauchecornite and tucekite. All these minerals are transition compounds between sulfosalts and pnictides.
Halide-sulfides (or halogeno-sulfides)
Ardaite, Pb17Sb15S35Cl9, dadsonite, Pb23Sb25S60Cl, and playfairite, Pb16(Sb, As)19S44Cl, are three examples of natural chloro-sulfosalts. Only the crystal structure of dadsonite is known (Makovicky et al., 2006b), but here, despite the very low Cl/S ratio, the Cl atom is fixed in a specific atomic position. Consequently Cl is essential for the formation of the mineral species.
Oxide (hydroxide)-sulfides
In scainiite, Pb14Sb30S54O5 (Moëlo et al., 2000), the O atoms are bound preferentially to Sb atoms, in a way analogous to that in kermesite Sb2S2O. Scainiite can be considered as an oxy-sulfosalt.
In cetineite, ~NaK5Sb14S6O18(H2O)6, both the SbS3 and SbO3groups are present, and K is bound almost exclusively, and Na completely, to O atoms (Sabelli et al., 1988; Wang & Liebau, 1999), with additional H2O molecules bound only to Na. This compound is thus a hydrated thio-oxysalt, like its Na-pure end-member, attensite (Sejkora & Hyrsl, 2007).
In sarabauite, (Sb4S6)(CaSb6O10), Sb atoms again bind both to S and O atoms, whereas Ca atoms are exclusively bound to O atoms (Nakai et al., 1978). This compound could be considered to be a "thio-oxysalt".
Apuanite and versiliaite are two Sb-containing oxy-sulfides, derived from the oxide schafarzikite (Mellini & Merlino, 1979). In apuanite, ideally Fe2+Fe43+Sb43+O12S, the Sb is bound only to O; thus the mineral cannot be considered to be an oxy-sulfosalt. In versiliaite, Fe22+(Fe33+Sb0.5?+Zn0.52+)
= 4Sb63+O16S, the situation is more complicated, as some Sb partly replaces Fe in a tetrahedral site, coordinated by 1 S and 3 O atoms. The Sb should correspond to Sb5+, which suggests that versiliaite is a combination of antimonite-antimonate with thio-antimonate.
Hydrated sulfosalts
In gerstleyite, Na2(Sb, As)8S13·2H2O (Nakai & Appleman, 1981), Sb is bound only to S atoms, whereas Na is bound to S atoms and H2O molecules; the mineral corresponds to a hydrated sulfosalt. Numerous synthetic hydrated sulfosalts have been synthesized.
Oxy-chloro-sulfides
Minor contents of O and Cl have been recently discovered in two new Pb–Sb sulfosalts, pillaite, Pb9Sb10S23ClO0.5, and pellouxite, (Cu, Ag)2Pb21Sb23S55ClO. Crystal-structure studies proved the O and Cl to be intrinsic components (Meerschaut et al., 2001; Palvadeau et al., 2004). These two minerals correspond to oxy-chloro-sulfosalts.
1.4. Conclusion
Taking into account the mineral species listed in Table 2 (more than 40 compounds) and those corresponding to the general formula [1] above (see the alphabetical index), as well as the borderline compounds, more than 260 mineral species belong to the "sulfosalt group" (sulfosalts and other chalcogeno-salts). There are also about 200 incompletely defined minerals (so-called "UM" – unnamed minerals) in the literature related to this vast group (Smith & Nickel, 2007), mainly because the chemical composition alone was determined by EPMA, which is generally easier to obtain than crystallographic data.
The "sulfosalt group" is as heterogeneous from a crystal-chemical point of view as, e.g., the silicate group. Consequently, a rigorous classification and nomenclature of sulfosalts is much more complicated than that of more restricted mineral groups which have been reexamined in the past by specific committees of the IMA (amphiboles, micas, zeolites...). As already mentioned, some sulfosalts fit perfectly in specific sulfide groups; for instance, most of the sulfostannates belong structurally within the sphalerite group. Only the vast group of sulfosalts with As3+, Sb3+, Bi3+ or Te4+ stands structurally as an almost separate family – this group is the topic of the present report. At the present stage of research, some groups of these sulfosalts can already be neatly classified on a crystal-chemical basis, whereas others await further discoveries for achieving the same depth of classification. The latter are grouped on purely chemical principles. The intention of the report is to assist further development of mineralogical studies in the field of complex sulfides.
2. Sulfosalts with As3+, Sb3+, Bi3+ or Te4+: chemistry and classification principles
2.1. General outline
There are various ways of classifying minerals. Some classifications are extrinsic (i.e., a paragenetic classification), but intrinsic ones are the best for development of the scientific field of mineralogy. Today, the deeper level of knowledge about minerals is that of their crystal structure (their "genetic code"); thus, the best classification ought to be a crystal-chemical classification. The first general crystal-chemical approach for sulfide minerals and related species was presented by Hellner (1958). Since the end of the 1960s, several mineralogical crystallographers have paid special attention to the sulfosalt group: Makovicky (1967), Nowacki (1969), Takéuchi & Sadanaga (1969), Povarennykh (1971), Wuensch (1974) and Edenharter (1976). In the following decade, some important aspects of the systematics of sulfosalts were emphasized: polymerization of complex anions and comparison with the classification of silicates (Ramdohr & Strunz, 1978; Kostov & Mineva-Stefanova, 1981; Nakai & Nagashima, 1983), problems of non-stoichiometry (Mozgova, 1984), modular analysis of the crystal structures (Makovicky, 1981, 1985a, 1989). Noteworthy is also the more recent work of Takéuchi (1997) on tropochemical cell-twinning (Remark: ‘cell-twinning’, defined by Takéuchi et al. (1979), differs from ordinary twinning – see Nespolo et al., 2004).
Table 3 presents the hierarchical structure of the system chosen for this review. Whenever possible, the system is based on the level of structural relationships among mineral species. Thus, for a large number of species the system is essentially a modular classification. The general definition of isotypic, homeotypic, and homologous series is given in "Nomenclature of Inorganic Structure Types" (Lima-de-Faria et al., 1990). The best known example of homeotypic series is certainly the aikinite–bismuthinite series (Topa et al., 2002a). A clear example of homologous series is that of the plagionite series, Pb3+2nSb8S15+2n (with n = 0, 1, 2, or 3). The lillianite series is more complex, with numerous homeotypic and homologous phases. Dimorphism has been recognized in several, relatively rare cases, e.g. for proustite versus xanthoconite, Ag3AsS3, for pyrargyrite versus pyrostilpnite, Ag3SbS3, or for clerite versus synthetic monoclinic MnSb2S4.
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Definition of many of these series is fortified by data for a number of synthetic sulfosalts that do not have natural equivalents (e.g., especially in Makovicky 1989, 1997, and Ferraris et al., 2004). The current presentation, which in many aspects is distinct from the general classification of Strunz & Nickel (2001), is not intended to be an overall crystal-chemical classification; rather, the presentation is a review of sulfosalt species, organized on the basis of chemistry and, where possible, on the basis of crystal chemistry. In the future, discovery of new sulfosalt species, as well as the resolution of up to now unknown crystal structures, will permit the development and improvement of this sulfosalt systematization.
2.2. Chemistry
The formula indicated is the ideal formula derived from a crystal-structure study or, if the species is poorly characterised, it is the simplified formula given for the type sample. For non-commensurate composite structures (for instance cylindrite), a reduced formula is given, which is always an approximation of the true formula.
Many sulfosalts have a complex chemistry, and frequently a minor chemical component appears to be essential for the stabilization of a mineral species (e.g., Cu in natural meneghinite, Cl in dadsonite). For a given species, the choice of the structural formula must indicate such minor components, whereas other elements, which are verifiably not essential (solid solution), can be excluded from the ideal formula as much as possible.
For the derivation of simplified formulae, it is important to know the principal substitution rules encountered among sulfosalts. For instance, if there is minor As together with major Sb, in many cases As can be totally substituted by Sb, and thus will disappear from the final structural formula. On the contrary, Cl even in low concentration (some tenths of a percent – see dadsonite), is expected to play a specific role and therefore, generally, must be retained in the formula. The avoidance or retention of a minor component necessitates a precise knowledge of the crystal structure, particularly of the specific atomic positions at which this minor component is located. Experimental studies are often the only way to obtain the compound without the minor component, and to verify that this pure compound has the same crystallographic characteristics. For instance, natural geocronite always contains minor amounts of As, but synthetic As-free geocronite is known (Jambor, 1968).
Table 4 presents a non-exhaustive list of various substitution rules encountered in sulfosalts. It represents a first step in the examination of new EPMA data, in order to correlate them more or less precisely with a chemical group of sulfosalts or a definite mineral species.
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The role of temperature can be important in controlling the substitution. Extended solid solutions at high temperature (in hydrothermal conditions: 300 to 400 °C) may be drastically restricted at low temperature (epithermal conditions). For instance this aspect is particularly important in the aikinite–bismuthinite series (Topa et al., 2002a). The substitution rules in Table 4 generally correspond to solid solutions, but the rules may also describe the homeotypic derivation of a species of complex chemistry, from another species that has a very close structure but a simpler composition (e.g., all Pb- and Cu-containing derivatives of bismuthinite in the aikinite–bismuthinite homeotypic series).
Careful EPMA of sulfosalts in routine conditions (for instance, 20 kV, 20 nA, counting time 10 s, compositionally close secondary standards) permits a very good mineral identification, if no minor element is omitted (down to 0.n wt.%). When such minor elements are present, and are not essential constituents (contrary to the 0.4 wt.% Cl in dadsonite, Pb23Sb25S60Cl), their subtraction using the substitution rules from Table 4 gives a simplified chemical formula that generally results in only one mineral species.
Remark: Exceptionally, some sulfosalts have a very low content of oxygen (0.n wt.%), which is nevertheless essential for their stability, as their crystal structure reveals a specific position for oxygen atoms (pillaite, pellouxite). EPMA would not be sufficient to prove the presence of oxygen within the structure, due to the easy formation of an oxidation film at the polished surface of the sample.
The search for minor elements is important both for mineral identification and for ore geochemistry and regional metallogeny, as is well known especially for the tetrahedrite series. Another example is the andorite series, which contains small amounts of Sn, Cd, and In in the Potosi district (Bolivia), whereas in Romania the characteristic minor elements are Mn and Fe.
2.3. Crystal structure and modular analysis
Knowledge of the crystal structure is not necessary for the validation of a new mineral species by the CNMNC of the IMA. Nevertheless, for sulfosalts having a large unit cell (e.g., most of the Pb sulfosalts), a solution of the crystal structure is today strongly recommended in order to prove the uniqueness of a new mineral species, and to reveal the role of minor components in the structure and composition. For these large structures it is also the only way to obtain a precise structural formula, and in some cases to decide whether a solid solution exceeds the 50 % limit in a characteristic site of the crystal structure, thereby giving a new isotypic mineral species.
Differences between the bonding strength and character of the metalloids (As, Sb, Bi) and metals, especially Pb, are less pronounced in sulfosalts than those between the bonding character in tetrahedral/triangular coordinations of Si, B, P, etc. and the associated cations in the relevant oxysalts. This difference, together with the variable types of coordination polyhedra of As, Sb and Bi and other crystal-chemical phenomena connected with the covalent character of bonding in the majority of sulfosalts, makes a polyhedral classification ineffective for most sulfosalt families. The approach at a higher level of organization in accordance with the principles of modular analysis seems to be the most efficient way to obtain a crystal-chemical classification of sulfosalts. Modular analysis of a crystal structure is based on the discrimination of sub-units called building blocks. This does not signify that interatomic bonding between constitutive building blocks is weaker than inside these blocks (they can be as strong, indeed stronger).
Typical for the combined arrays of metalloids and Pb and some other metals (e.g., Ag), as well as for some fairly pure Bi or Sb arrays, are extensive building blocks. The blocks approximate the topology of the PbS structure (cases with low activity of lone electron pairs) or of the SnS structure (TlI, TlSbS2 are also approximations) for arrays that have well-expressed activity of lone electron pairs. lone electron pairs of metalloids are accommodated by the archetypal motif (often congregating in common spaces, so-called "lone electron pair micelles") whereas the contact between blocks takes place via mutually non-commensurate surfaces or by means of unit-cell twinning (details in Makovicky 1989, 1997). Structures with low contents of metalloids tend to follow the topologies dictated by the principal metals, eventually modified to satisfy the metalloid requirements as well.
The structural principles outlined in the preceding paragraph commonly lead to the presence of homologous series differing in the size of blocks but not in the principles of their recombination into one structure, or to more general families of related structures when the simple homologous expansion is hindered on structural grounds. Increase in the block size alters the Pb(Sn)/metalloid ratio in favour of divalent metals; the same may happen in favour of combined AgBi or, rarely, even CuBi arrays. More extensive arrays and less expressed lone-electron-pair character may be favoured by elevated temperatures and by the substitution of S by Se or even Te.
Blocks of these archetypal structures can be, according to the general vocabulary:
Numerous Pb sulfosalts, among them the boulangerite plesiotypic series, have been described using an intermediate category between 2D- and 1D blocks. The intermediate category is the "rod-layer" type, which results from the connection of rods along one direction (Makovicky, 1993).
The description of the general organization of a crystal structure involves the discrimination of the constitutive building blocks, and how they are interconnected. The description thus permits definition of the type of architecture of the crystal structure. The main part of the architectural types is based on a single type of building block. A significant part results in the combination of two types of blocks, as in some homologous series. The most complex architectural type is the boxwork type, a combination of three distinct blocks, as exemplified by the crystal structure of neyite (Makovicky et al., 2001a).
2.4. Non-stoichiometry in sulfosalts
The concept of non-stoichiometry in sulfosalts has been promoted especially by Mozgova (1984, 2000), and is discussed briefly here by using both a general approach and specific examples. The most common case of non-stoichiometry corresponds to various solid solutions, as presented in Table 4. Some substitution rules, isovalent or heterovalent, do not change the total number of atoms in the structural formula (= in the unit cell); other substitutions imply filling, or creating vacancies, which changes the total number of atoms present.
At the opposite end of the scale, syntactic intergrowths correspond to a mixture, at the (pseudo-)crystal level, of 3D domains of (at least) two species with similar crystal structures. Such intergrowths have various origins and present various textures (exsolution process, myrmekites by decomposition or substitution, simultaneous precipitation...). When the size of domains decreases to a micrometer scale, it becomes difficult to recognize the domains even at the highest magnification with a metallographic microscope, and microprobe analysis typically shows analytical dispersion around theoretical stoichiometric formulae; examples are the plagionite (Mozgova & Borodaev, 1972) and andorite–fizélyite (Moëlo et al., 1989) homologous series.
Intergrowths of the aforementioned type may be present even at a nanometric scale, and are visible with high-resolution techniques such as electron microscopy. SEM may give good images, which generally reveal a strong geometrical anisotropy of intergrowths, towards 2D domains with more or less pronounced stacking disorder. One of the best approaches is HRTEM, which permits a precise crystallographic characterisation of associated sulfosalts. These species correspond to two closely related members of a homologous series (Pring et al., 1999), exceptionally even to more distinct species (Pring & Etschmann, 2002; Ciobanu et al., 2004).
The most complex cases encountered in the sulfosalt group are exsolution aggregates of the bismuthinite series, wherein some samples correspond to a nanometric association of two or three members, some of them with their own deviations from a simple stoichiometry, which are related to a solid-solution mechanism (Topa et al., 2002b).
Of course, these various types of non-stoichiometric members will give different X-ray signatures in powder diagrams or by single-crystal study.
A special example of non-stoichiometry is that of sulfosalts with layered composite non-commensurate structure (cylindrite and related compounds – Makovicky & Hyde, 1981, 1992). In these sulfosalts, each of the two constituent layers may have a stoichiometric formula, but the non-commensurate (non-integer) ratio between one or two pairs of in-plane parameters results in a "non-stoichiometric" (i.e., complex) structural formula.
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Part II. Review of sulfosalt systematics |
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TopAbstractPreamblePart I. Revision of...Part II. Review of...3. Lead sulfosalts based...4. Sulfosalts based on...5. Specific Tl(Pb) and...6. Sulfosalts with an...7. Unclassified sulfosalts8. ConclusionAppendix: Additional list of...References |
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Introduction: general presentation of sulfosalt species
This general presentation takes into account the sulfosalt species given by "Fleischer’s Glossary of Mineral Species" (Mandarino & Back, 2004) (see also Blackburn & Dennen, 1997; Martin & Blackburn, 1999, 2001; Martin, 2003), plus the new species published or approved recently by the CNMNC-IMA (see its website). The presentation is concerned with more than 220 sulfosalt species, for which an alphabetical list is given at the end of the text, together with an appendix that lists discredited species.
As the crystal-chemical classification of sulfosalts is incomplete at present, the following general presentation of sulfosalt mineral species is subdivided into large chemical groups. Within each group, subdivisions are generally based on well-defined structure types.
Sulfosalt species whose specific crystal structure does not have a close relationship to those of other species are indicated separately as "Single type". If the crystal structure of a species is not known, this species is classified, as much as possible, with sulfosalts that have a similar chemistry.
About the references
To reduce as much as possible the number of references cited in this review, only the following have been included:
Crystallographic data (unit-cell parameters, symmetry, space group) have been avoided, except when a change in symmetry or space group appears crucial for the distinction between two very close species (e.g., giessenite versus izoklakeite).
All other references and basic data are available in fundamental books on systematic mineralogy (e.g., Strunz & Nickel, 2001; Mandarino & Back, 2004), as well as in PDF (JCPDF) or ICSD (FIZ – Karlsruhe) databases. Concerning the crystal structures, especially noteworthy is the extensive work of Dr Y. Matsushita, who has compiled systematically all chalcogenide and related structures, both of natural and synthetic phases. Access to the data-library is free at http://www.crystalmaker.co.uk/library/chalcogenides.html.
Where problems are present regarding the definition of a species, relevant comments are given after the presentation of each species or group. The aim is to present the current status of sulfosalt definition, nomenclature and classification for all specialists interested in this field of research, thereby pointing out various unsolved questions and facilitating the discovery of new mineral species.
1. Sulfosalts with atom ratio of cation/chalcogen = 1
1.1. Binary sulfosalts (MPnCh2), where M = univalent cation (Cu, Ag, Tl); Pn = pnictogen (As, Sb, Bi); Ch = chalcogen
These sulfosalts are presented according to the organisation of pnictogen polyhedra.
1. Matildite isotypic series (trigonal derivatives of PbS, according to (PbS)111 slices)
All these structures could also be considered as derivatives of the CdI2 archetype (single layer of BiCh6 octahedra), with Ag atoms intercalated between the layers (so-called "intercalation compounds"). However, these old structure determinations appear to be (pseudo)cubic approximations, as it is unrealistic to consider regular BiCh6 octahedra because of the lone-electron-pair of Bi3+.
2. Aramayoite isotypes
3. (Single type)
4. (Single type) (sheared derivative of SnS archetype)
5. (Single type)
6. (Single type) Cyclic trigonal
7. Emplectite isotypic series
8. Weissbergite homeotypic pair
-uni et al. (1995). Weissbergite is a direct substitution derivative of the SnS archetype, whereas lorandite is a stacking variant related to this archetype with a double-layer periodicity.
| Schapbachite and schirmerite (Type 1): the same compound? Schapbachite, initially defined as the cubic form of AgBiS2, was subsequently discredited because it is a high-temperature form that always decomposes at low Tto its trigonal dimorph, matildite. Schapbachite, was recently redefined by Walenta et al.(2004) through the study of a sample containing a significant amount of Pb (~ 20 % of the cation sum). This Pb content seems necessary for the stabilization of schapbachite, and ought to appear in the chemical formula. Previously, Bortnikov et al. (1987) discovered a mineral ("Phase I") that has the composition originally assigned to schirmerite (Type I), Ag4PbBi4S9 (that is, strictly in the AgBiS2–PbS pseudo-binary system), but without X-ray data. This schirmerite is very close to the stable form of schapbachite (Ag4PbBi4S9 = Ag0.445Pb0.11Bi0.445S); however, in the absence of crystallographic data, it is not possible to conclude whether schirmerite is equivalent to schapbachite or corresponds to an ordered dimorph.
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1.2. Ternary sulfosalts (M1+M22+PnS3)
1. Freieslebenite family (3-dimensional PbS-like arrays)
Freieslebenite (isotypic) series
Related
2. Bournonite isotypic series
ekite, CuPbBi(S, Se)3 3. Mückeite isotypic series
4. (Single type)
1.3. Quaternary sulfosalts (M1+M2+M32+Pn2S5)
Hatchite isotypes
2. Lead sulfosalts with a pronounced 2D architecture, their derivatives with a composite structure, and related compounds
2.1. Layered sulfosalts related to the tetradymite archetype
Tetradymite is the archetype of a complex group of chalcogenides, composed of numerous natural and synthetic compounds, of a great interest in the field of thermoelectrics. All crystal structures are derivatives of a NaCl distorted close packing, generally with trigonal symmetry. Within this group, minerals can be classified according to two complementary homologous series:
Details concerning the crystal chemistry of minerals of this group, especially complex Pb–Te derivatives, are presented by Cook et al. (2007a, 2007b). These Pb derivatives relate to the chemical definition of sulfosalt; but one must point that, in all this group, Bi3+ ought to present a fairly its octahedral coordination, indicating a weak stereochemical activity of lone electron pair. Within this group are six Pb-Bi sulfosalts, among which five belong to the aleksite homologous series.
Aleksite homologous series, Pb(n–1)Bi2Ch(n+2)
In this series, the c periodicity corresponds to three seven-atoms-thick layers Ch–Me–Ch–Me–Ch–Me–Ch, with the central Me atom probably corresponding to Pb, and the two marginal ones to Bi.
Remarks: 1. Higher or combined members of the aleksite series require detailed X-ray structure determinations. 2. Cannizzarite (see 2.3) is a composite structure with one of the two layers of the tetradymite type. 3. "Platynite", commonly given as PbBi2(Se, S)7 in the literature, has been discredited (Holstam & Söderhielm, 1999).
2.2. Composite structures from alternating pseudohexagonal and PbS/SnS-like tetragonal layers
1. Commensurate structures
2. Non-commensurate structures
| Potosiite and incaite: two varieties of franckeite Franckeite has a composite layered structure, with in-plane non-commensurability (Makovicky & Hyde, 1981). One layer "H" is of the CdI2 type, (Sn, Fe, Sb)S2, like in cylindrite (Makovicky, 1974); the second one "Q" is of the SnS/TlI type, four atoms thick (twice that of cylindrite): (Pb, Sn, Sb, Fe?)4S4. Sn is tetravalent in H, divalent in Q, where it substitutes for divalent Pb. The synthetic composite compound [(Pb, Sb)S]2.28NbS2 (Lafond et al., 1997) has the same Q layer as franckeite; here Sb is exclusively in the two central atomic planes of this layer. Wolf et al (1981 – definition of potosiite) and Mozgova et al (1976) pointed out that franckeite is crystallographically similar to potosiite and incaite (defined by Makovicky, 1974 and 1976). On the basis of the crystal-chemical model, potosiite is Sn2+-poor franckeite (Makovicky & Hyde, 1992), and incaite is Sn2+-rich franckeite, always with Pb >Sn2+ in natural samples. Thus, potosiite and incaite correspond to varietal compositions in the franckeite solid-solution field (Mozgova et al, 1976) and should be taken of the list of mineral species. In synthetic samples, Sn/Pb can surpass 1 (up to Pb-free franckeite and cylindrite – Moh, 1987). The discovery of such samples in nature would permit redefinition of incaite as a new mineral species.
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Type 2
Remark: "Wittite B" of Large & Mumme (1975) corresponds to proudite (Mumme, 1976).
| Wittite: original species, or Se-rich cannizzarite? Wittite and cannizzarite obey the same crystal-chemical model of composite, non-commensurate structure: a (Pb, Bi)2(S, Se)2 layer "Q" alternating with a (Bi, Pb)2(S, Se)3 layer of the tetradymite type (i.e., a double-octahedral layer). The main difference in the structural formula is the high Se/S ratio of wittite (Mumme, 1980a). This Se/S atomic ratio never exceeds 1, but the tetradymite-type layer is very probably enriched in Se relative to the Q layer (Mozgova et al, 1992). Precise knowledge of the Se partitioning between the two layers is necessary to validate wittite as a species, if Se/S > 1 in the tetradymite-type layer. On the contrary, if in natural compounds the Se/S atomic ratio is always below 1 in the tetradymite-type layer, wittite would correspond to a Se-rich variety of cannizzarite. The pure Se derivative of cannizzarite has been synthesized recently, and its structure solved (Zhang et al, 2005). This complete Se-forS substitution enhances the possibility of validating wittite.
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2.3. Commensurate composite derivatives of cannizzarite
In this group, all structures show an alternation of two types of ribbons or stepped layers resulting from the fragmentation of the two layers comprising the cannizzarite-like structure (one pseudo-quadratic, of the PbS archetype, the other pseudo-hexagonal, of the CdI2 archetype). Three factors govern structural variations: 1) the thickness of each layer/ribbon; 2) the widths between consecutive planes of slip/shear and the width of their interface (according to a mQ/nH ratio); and 3) the spatial offset of ribbons of each type around planes of step (relative to the original layer).
1. Cannizzarite plesiotypic derivatives
This sub-group is described by Makovicky (1997).
2. Boxwork derivatives of cannizzarite
This boxwork type results from a combination of three types of building blocks. There are two types of ribbons (slab fragments) alternating to form complex slabs. These slabs are separated by a layer or ribbon-layer (here three atoms in thickness), giving the final boxwork architecture. One type of ribbons in the complex slabs and the latter layer (both with surfaces of pseudotetragonal character) form a boxwork system of partitions; the remaining type of fragments fills the boxes.
Remark: Complex Pb/Sb oxy-(chloro)-sulfosalts (scainiite, pillaite and pellouxite) belonging to the zinkenite plesiotypic series can also be described by a similar boxwork architecture.
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3. Lead sulfosalts based on large 2D fragments of PbS/SnS archetype |
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TopAbstractPreamblePart I. Revision of...Part II. Review of...3. Lead sulfosalts based...4. Sulfosalts based on...5. Specific Tl(Pb) and...6. Sulfosalts with an...7. Unclassified sulfosalts8. ConclusionAppendix: Additional list of...References |
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The definition and crystal chemistry of this homologous series were presented by Makovicky (1977), and Makovicky & Karup-Møller (1977a, 1977b). Additional data were given in Makovicky & Bali-uni (1993). All structures are based on PbS-like slabs of various thickness (number N of octahedra). Each homologue type is symbolized as NL, or as N1,N2L (when there are two slabs of distinct thickness).
1. Lillianite homeotypic series (4L)
=1.06Pb0.88Sb3.06S6 (~And106)
| Andorites IV and VI: two distinct species These two minerals have distinct symmetry, with very close but distinct chemistry, without solid solution, as they are frequently observed in close epitactic intergrowth (Moëlo et al, 1984a, 1989). Thus they correspond to two homeotypic species, with distinct superstructures (4c and 6c, respectively) and not to two polytypic forms of the same species. The study of Sawada et al (1987) solved the true (6c) crystal structure of andorite VI (or "senandorite"). Nakaséite: a variety of andorite VI
Nakaséite, defined by Ito & Muraoka (1960) as a Cu-rich derivative of andorite with a superstructure of (c x 24), was considered by Fleischer (1960) to be a polytypic variety of andorite (andorite XXIV). A later detailed examination of minerals of the andorite–fizélyite series (Moëlo et al, 1989) confirmed that nakaséite is an oversubstituted, Cu-rich (~ 1 wt.%) variety of andorite VI, with a formula close to (Ag0.93Cu0.13) Ramdohrite: species, or variety of fizélyite? Ramdohrite from the type deposit has a significant Cd content (Moëlo et al, 1989) and is compositionally close to fizélyite (ideally And68.75 and And62.5, respectively), but it is not known if there is a solid solution (ramdohrite = Cd-rich variety of fizélyite?) or an immiscibility gap (ramdohrite =specific species?). Fizélyite from Kisbánya (Romania) shows exsolutions of a (Mn, Fe)-rich variety of ramdohrite; such exsolutions correspond to a specific species (same study). A crystal-structure study of fizélyite from the type deposit is necessary to confirm the distinction between these two species. "Bursaite" Bursaite from the type deposit corresponds to Ag-poor lillianite (Makovicky & Karup-Møller, 1977b). A new occurrence (Shumilovskoe, West Transbaikal) studied by Mozgova et al (1988) was found by X-ray powder and electron-microdifiaction data to be an intergrowth of two lillianite-related phases, each with a distinct unit cell. The electron-microprobe composition, which represents a composite from the two phases, indicates a Pb deficit (N ~ 3.83). Bursaite would correspond to the Pb-poor phase, with cation vacancies.
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2. Heyrovsk
ite homeotypic series (7L)
ite, Pb6Bi2S9 ite as a specific mineral species. 
