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8-1-2008 Recommended Nomenclature for the Sapphirine and Surinamite Groups (Sapphirine Supergroup) Edward S. Grew University of Maine - Main, [email protected]
U. Hålenius
M. Pasero
J. Barbier
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Repository Citation Grew, Edward S.; Hålenius, U.; Pasero, M.; and Barbier, J., "Recommended Nomenclature for the Sapphirine and Surinamite Groups (Sapphirine Supergroup)" (2008). Earth Science Faculty Scholarship. 168. https://digitalcommons.library.umaine.edu/ers_facpub/168
This Review is brought to you for free and open access by DigitalCommons@UMaine. It has been accepted for inclusion in Earth Science Faculty Scholarship by an authorized administrator of DigitalCommons@UMaine. For more information, please contact [email protected]. Mineralogical Magazine, August 2008, Vol. 72(4), pp. 839–876
Recommended nomenclature for the sapphirine and surinamite groups (sapphirine supergroup)
1 2 3 4 E. S. GREW ,U.HA˚ LENIUS ,M.PASERO AND J. BARBIER 1 Department of Earth Sciences, University of Maine, 5790 Bryand Research Center, Orono, 04469-5790 Maine, USA 2 Department of Mineralogy, Swedish Museum of Natural History, Box 50007, SE-104 05 Stockholm, Sweden 3 Dipartimentodi Scienze della Terra, Universita` di Pisa, Via S. Maria 53, I-56126 Pisa, Italy 4 Department of Chemistry, McMaster University, Hamilton, Ontario, Canada L8S 4M1 [Received 3 September 2008; Accepted 13 October 2008]
ABSTRACT Minerals isostructural with sapphirine-1A, sapphirine-2M, and surinamite are closely related chain silicates that pose nomenclature problems because of the large number of sites and potential constituents, including several (Be, B, As, Sb) that are rare or absent in other chain silicates. Our recommended nomenclature for the sapphirine group (formerly aenigmatite group) makes extensive use of precedent, but applies the rules to all known natural compositions, with flexibility to allow for yet undiscovered compositions such as those reported in synthetic materials. These minerals are part of a polysomatic series composed of pyroxene or pyroxene-like and spinel modules, and thus we recommend that the sapphirine supergroup should encompass the polysomatic series. The first level in the classification is based on polysome, i.e. each group within the supergroup corresponds to a single polysome. At the second level, the sapphirine group is divided into subgroups according to the occupancy of the two largest M sites, namely, sapphirine (Mg), aenigmatite (Na), and rho¨nite (Ca). Classification at the third level is based on the occupancy of the smallest M site with most shared edges, M7, at which the dominant cation is most often Ti (aenigmatite, rho¨nite, makarochkinite), Fe3+ (wilkinsonite, dorrite, høgtuvaite) or Al (sapphirine, khmaralite); much less common is Cr (krinovite) and Sb (welshite). At the fourth level, the two most polymerized T sites are considered together, e.g. ordering of Be at these sites distinguishes høgtuvaite, makarochkinite and khmaralite. Classification at 2+ the fifth level is based on XMg = Mg/(Mg + Fe ) at the M sites (excluding the twolargest and M7). In principle, this criterion could be expanded to include other divalent cations at these sites, e.g. Mn. To 2+ date, most minerals have been found to be either Mg-dominant (XMg > 0.5), or Fe -dominant (XMg < 0.5), at these M sites. However, XMg ranges from 1.00 to 0.03 in material described as rho¨nite, i.e. there are two species present, one Mg-dominant, the other Fe2+-dominant. Three other potentially new species are a Mg-dominant analogue of wilkinsonite, rho¨nite in the Allende meteorite, which is distinguished from rho¨nite and dorrite in that Mg rather than Ti or Fe3+ is dominant at M7, and an Al- dominant analogue of sapphirine, in which Al > Si at the two most polymerized T sites vs. Al < Si in sapphirine. Further splitting of the supergroup based on occupancies other than those specified above is not recommended.
KEYWORDS: nomenclature, aenigmatite, sapphirine, surinamite, chain silicates.
Statement of the problem
THE sapphirine group and related mineral surinamite are chain silicates that pose nomen- clature problems because of the large number of * E-mail: [email protected] sites and potential constituents, including several DOI: 10.1180/minmag.2008.072.4.839 (Be, B, As, Sb) that are rare or absent in related
# 2008 The Mineralogical Society E. S. GREW ET AL. chain silicates, together with extensive cation CNMMN (now CNMNC) or in the process of disorder at these sites and the difficulty of being considered by the CNMNC. Our approach deriving Fe valence ratios from electron micro- follows more the direction taken by Hawthorne probe analyses; the question of Ti valence arises and Oberti (2006) for amphiboles, for which in rho¨nite from the Allende meteorite. We have cation sites were grouped for classification (Hatert chosen sapphirine rather than aenigmatite to name and Burke, 2008), rather than treated individually the supergroup and larger group therein because as in the unique-name system adopted by Johnsen sapphirine was the first of these minerals to be et al. (2003) for eudialyte. Our criteria distinguish discovered, chemically analysed and to have its species in a systematic fashion, that is, we have crystal structure refined. There are 15 independent identified critical individual sites or several sites cationic sites in the centrosymmetric triclinic taken together that can be used as criteria. These members of the sapphirine group, 12 in the related criteria include a mixture of chemical and monoclinic mineral surinamite and over 20 in crystallographical properties. Nonetheless, it members lacking a centre of symmetry (welshite) appears that full application of our nomenclature or having a superstructure (khmaralite). Applying will require crystal structure refinements. the standard CNMNC guidelines (Nickel and Our recommended nomenclature has been Grice, 1998) toeach site individually wouldresult approved by the Commission on New Minerals, in a plethora of species that would be difficult to Nomenclature and Classification, International distinguish on a routine basis and have little Mineralogical Association. geological or petrological significance. However, failing to take into account cation distribution and order could result in overly broad species Def|nition of the sapphirine and surinamite definitions. Complicating the situation in the groups sapphirine group are superstructures, polysoma- Strunz and Nickel (2001) broadened the tradi- tism and polytypism and changes in symmetry tional aenigmatite or aenigmatite-rho¨nite group dictated by cation order. Because most (e.g. Kunzmann, 1999) toinclude the closely sapphirine-group minerals have triclinic related minerals sapphirine and surinamite. symmetry, it took some time to agree on a unit Minerals in this group are monoclinic and triclinic cell, namely the Delaunay cell, which was first chain silicates containing kinked, winged chains proposed by Kelsey and McKie (1964) for of tetrahedra and walls of octahedra. Strunz and aenigmatite and generally adopted afterwards. Nickel (2001) alsosuggested that jonesitemight Todate, criteria applied todistinguish one be a related mineral, but a subsequent crystal species from another have been applied ad hoc, structure refinement of jonesite did not bear this making use of site occupancies when available, out (Krivovichev and Armbruster, 2004). Gaines but relying on stoichiometry in the absence of a et al. (1997) suggested that magbasite, 2+ crystal structure refinement. In many cases KBa(Mg,Fe )6(Al,Sc)Si6O20F2,whichwas recognizing a new species seemed relatively described by Semenov et al. (1965), could be in easy because its composition differed so much the sapphirine group, but there is no evidence for from existing species, e.g. Ca vs. Na, presence of such a relationship. Only a powder diffraction Be, Sb, As or B. However, other species proved pattern was reported in the original description more difficult, most recently makarochkinite, (single crystal data could not be obtained) and it where detailed crystallographic study was differs substantially from that of aenigmatite needed to demonstrate ordering of Ti at a single reported by Kelsey and McKie (1964). The M site. chemical composition recalculated on a Kunzmann (1999) proposed a classification for 28 cation basis (cf. 15 cations in the given the sapphirine group that was not reviewed by the formula) gave 4.9 F, 1.6 Ba and 1.8 K, none of CNMMN. His classification included only the Na- which are reported in comparable quantities, if at and Ca-bearing members, aenigmatite and rho¨nite all, in sapphirine-group minerals and compounds subgroups, respectively, and was based largely on (cf. 4OH in a synthetic isostructural with composition with much less reliance on crystal aenigmatite, Yang and Konzett, 2000). structure. Consequently, as models to follow in We agree with Strunz and Nickel (2001) that developing a classification, we have sought sapphirine and aenigmatite should be included in examples from other mineral groups that have the same group, but we disagree that surinamite been reviewed recently and approved by the also belongs there. Instead, classification of
840 SAPPHIRINE AND SURINAMITE NOMENCLATURE
sapphirine and related minerals are better under- chemical analysis, was reported by Stromeyer stood in terms of a polysomatic series involving (1819, 1821), whoretained Giesecke’s name one clinopyroxene-like module (or a close-packed ‘saphirine’, later changed tothe present spelling isotype of clinopyroxene like CoGeO3, which was with double p. Over a century of study (e.g. refined by Peacor, 1968) and one spinel module Ussing, 1889; Lorenzen, 1893), including single- (Dornberger-Schiff and Merlino, 1974; Christy crystal X-ray diffraction (XRD) (Goßner and and Putnis, 1988; Barbier and Hyde, 1988; Mußgnug, 1928; Kuzel, 1961; McKie, 1963; Bonaccorsi et al., 1990, Arakcheeva and Ivanov, Fleet, 1967), gave a range of compositions from 1993; Merlinoand Pasero,1997; Gasparik et al., Mg2Al4Si2O10 tosomewhatricher in Al than 1999; Zvyagin and Merlino, 2003), which more Mg7Al18Si3O40, the formula given in Table 1; specifically defines the relationship of surinamite these formulae are related by the Tschermak’s tosapphirine and aenigmatite and leaves openthe substitution Mg + Si > 2Al (e.g. Vogt, 1947). possibility of other polysomes being included in However, a fuller understanding of its crystal the future. Thus, we are introducing the concept chemistry was not possible until Moore’s (1968; of a sapphirine supergroup that would encompass 1969) successful refinement of the structure of all the polysomes. The sapphirine group includes monoclinic sapphirine from Fiskenæsset. Merlino only the polysome consisting of one clino- (1970, 1972) recognized that the crystal structures pyroxene or pyroxene-like module and one of sapphirine, aenigmatite, krinovite and rho¨nite, spinel module. The sapphirine group can be were all closely related, and thereby provided the divided into three subgroups on the basis of the conceptual basis for the sapphirine group. Merlino dominant cations in the polyhedra outside the (1980) refined the crystal of the triclinic polytype, octahedral walls; a fourth subgroup needs more further linking the sapphirine subgroup with the study (Table 1). In the aenigmatite and rho¨nite other two subgroups. In addition to the 1A and 2M subgroups, the octahedral walls are cross-linked polytypes, which dominate natural sapphirine intocontinuoussheets by 7 À8coordinated (e.g. Christy, 1989), Merlinoand Pasero(1987) polyhedra containing Na and Ca, respectively. and Christy and Putnis (1988) found 3A,4M and The corresponding sites in the sapphirine 5A polytypes as domains ranging from less than subgroup are 6 coordinated, and the octahedral 100 A˚ toseveral thousanda ˚ngstro¨ms thick. walls are not cross-linked. Grew (1981) described a ‘beryllian sapphirine’ The surinamite group would include the containing 1.4 Be per formula unit of 28 cations polysome consisting of two pyroxene modules from Zircon Point, a small exposure in Khmara and one spinel module. To date, there is only one Bay, Enderby Land, East Antarctica. Christy known natural compound in this group occurring (1988), using transmission electron microscopy as an independent phase, surinamite itself, and (TEM), recognized this mineral as having a thus designating a surinamite group anticipates superstructure with doubled a axis (P21/c the recognition of more species. The surinamite setting). Refinement of the structure using XRD structure differs from those of the sapphirine became possible only when the very weak group in the proportion of wing to chain superstructure reflections could be measured, tetrahedra: 20% vs. 33%, and in the position of which Barbier et al. (1999) succeeded in doing the wings, which are all on one side of the chains with a Siemens diffractometer and a SMART area in surinamite, but on both sides in the sapphirine detector, and thus were able to demonstrate group. ordering of Be at alternating T2 and T3 sites in doubled tetrahedral chains. The refinement served todistinguish khmaralite fromsapphirine-2 M Historical synopsis both by the presence of the 26a superstructure Sapphirine, khmaralite and the predominance of Be at one tetrahedral Sapphirine is the first sapphirine-group mineral to site. The name ‘beryllosapphirine’ was not be discovered, chemically analyzed and to have applied by Barbier et al. (1999) because they its crystal structure refined. Giesecke found reasoned that a mineral of this name should have sapphirine in 1809 at Fiskenæsset, West the same space group as sapphirine-2M and Greenland, and called it ‘blauer Diamantspath similar cell parameters, and thus they named the (saphirine)’ in his catalogues (Bøggild, 1953). mineral for the locality. Grew et al. (2000) The first description of Giesecke’s mineral, reported a weak 26a superstructure in a sample including a density measurement and full from a second locality in Khmara Bay that
841 TABLE 1. Minerals of the sapphirine supergroup, including possible species not yet approved by IMA CNMNC (in italics)
Mineral symmetry End-member formula* First report; structure refinement{
Sapphirine group:
3+ { GREW S. E. Krinovite Triclinic P1¯ Na4(Mg8Cr4 )O4[Si12 O36 ] Olsen and Fuchs (1968); Bonaccorsi et al. (1989) Rho¨nite subgroup: Ca-dominant 3+ { Rho¨nite Ca4(Mg8Fe2 Ti2)O4[Si6Al6O36 ] Soellner (1907); Bonaccorsi et al. (1990) 842 2+ 2+ Unnamed Fe -analogue of rho¨nite Ca4(Fe10 Ti2)O4[Si8Al4O36 ] Gru¨nhagen and Seck (1972); Havette et al. (1982); Olsson (1983); Gamble and Kyle (1987); TAL. ET Kuehner and Irving (2007); Treiman (2008) 3+ 3+ 4+ { Unnamed Ti -bearing Mg-analogue of rho¨nite Ca4(Mg7AlTi2 Ti2 )O4[Si5Al7O36 ] Fuchs (1971); Bonaccorsi et al. (1990) (Allende meteorite) Triclinic P1¯ ¯ 3+ 3+ Dorrite Triclinic P1 or P1Ca4(Mg3Fe9 )O4[Si3Al8Fe O36 ] Cosca et al. (1988) Serendibite Triclinic P1¯ Ca4(Mg6Al6)O4[Si6B3Al3O36 ] Prior and Coomaraswamy (1903); {Van Derveer et al. (1993) ¯ 2+ 3+ { Høgtuvaite Triclinic P1 Ca4(Fe6 Fe6 )O4[Si8Be2Al2O36 ] Grauch et al. (1994); Grew et al. (2005) ¯ 2+ 3+ { Makarochkinite Triclinic P1 Ca4(Fe8 Fe2 Ti2)O4[Si8Be2Al2O36 ] Polyakov et al. (1986); Yakubovich et al. (1990); {Grew et al. (2005) 5+ 3+ { Welshite Triclinic P1¯ Ca4(Mg9Sb3 )O4[Si6Be3AlFe2 O36 ] Moore (1978); Grew et al. (2007) Fe-Ga subgroup Unnamed Fe-Sn-Ga-Ge mineral (Fe,Ga,Sn,Zn)16 O4[(Ga,Ge)12 O36 ] Johan and Oudin (1986) Surinamite group
* Except for unnamed Al analogue of sapphirine, for which the formula was calculated from electron microprobe data. { Only complete refinements listed. SAPPHIRINE AND SURINAMITE NOMENCLATURE
contained 0.87À1.05 Be per 28 cations, i.e. the (1887, 1890) confirmed by detailed comparison of appearance of the superstructure defining khmar- the chemical composition and crystal alite coincides with Be occupancy approaching morphology. Thus, Bro¨gger (1887, 1890) gave 50% at the T2 and T3 sites considered together. aenigmatite priority, and considered the name ‘cossyrite’ to be only a synonym. Discredition of ‘cossyrite’ was complete when powder X-ray data Aenigmatite, wilkinsonite, krinovite by A.S. Anisimova confirmed its identity as Breithaupt (1865) simultaneously introduced two aenigmatite (Fleischer, 1964). new monoclinic minerals ‘ko¨lbingite’ and ‘ainig- Bro¨gger (1887, 1890) suggested that aenigma- matite’, which he discovered in samples of tite could be a triclinic member of the amphibole peralkaline plutonic rocks from the Ilı´maussaq group despite the nearly 10º difference in the complex, Kangerdluarssuk, Greenland (Bøggild, angle between the cleavages (66º vs. 56º for 1953). He named the first for his late friend arfvedsonite) and a significant difference in axial Ko¨lbing and the second from the Greek ainigma ratio, both of which he attributed to substitution of for its enigmatic nature by comparison with Si by Ti. In contrast, Soellner (1909) placed ‘ko¨lbingite’; indeed, aenigmatite has proven to ‘cossyrite’ and aenigmatite in a separate group be a most appropriate name. Breithaupt (1865) that was on a par with pyroxenes and amphiboles. reported both minerals as being greenish to X-ray studies by Goßner and Mußgnug (1929) velvet-black in colour and having the identical showed that aenigmatite is not related to prismatic habit, but differing in streak, density amphibole, and this conclusion was confirmed and hardness, and suggested that ‘ainigmatite’ by morphological crystallography (Palache, 1933) was pseudomorphous after ‘ko¨lbingite’. No and chemical analyses (Fleischer, 1936). On the quantitative analysis was given for either basis of literature data and new analyses, Kelsey mineral; preliminary analyses gave Ca, Fe and and McKie (1964) settled on the now accepted Si, with Fe largely ferrous in ‘ko¨lbingite’ and crystallographic orientation (Delaunay cell), unit ferric in aenigmatite. Lorenzen (1882) doubted cell content and formula (Table 1). Thompson the pseudomorphous nature of aenigmatite and Chisholm (1969) synthesized aenigmatite because the aenigmatite crystals available tohim with the composition deduced by Kelsey and were all very fresh and unaltered (he did not have McKie (1964). any crystals of ‘ko¨lbingite’ to compare). Forsberg Three groups simultaneously solved the crystal (in Bro¨gger, 1887, 1890) was the first toobtaina structure of aenigmatite: Merlino (1970); Cannillo complete analysis of the major constituents in and Mazzi; and Fang, Robinson and Ohya; the aenigmatite including Ti, which he found was latter twogroups reported their results in a joint major. Bro¨gger (1887, 1890) alsogave some publication (Cannillo et al. 1971). Choi (1983) and optical properties of aenigmatite, and thus was Choi and Burns (1983) reported Mo¨ssbauer able tofinally confirmits validity as a mineral spectroscopic evidence for the presence of Fe3+ species. Bro¨gger (1887, 1890) alsosuggested that on tetrahedral sites. A new refinement and ‘ko¨lbingite’ was an intergrowth of arfvedsonite Mo¨ssbauer spectrum (Grew et al., 2008) confirm and aenigmatite by noting that the density and the essential features reported earlier, but bring streakcolorof‘ko¨lbingite’ are intermediate greater precision to cation ordering in aenigmatite. between those of arfvedsonite and aenigmatite. Hodges and Barker (1973) reported extensive Ussing (1898) was able toexamine a ‘ko¨lbingite’ solid solution by the substitution of Fe2+ +Tiby crystal from the material studied by Breithaupt, 2Fe3+ between ‘ideal aenigmatite’ and the and showed that similar specimens in the titanium-free aenigmatite which had been synthe- Mineralogical Museum in Copenhagen consisted sized by Ernst (1962) in the Na-Fe-Si-H-O of aenigmatite coated with aegirine, leading him system. Duggan (1990) described the latter as toconcludethat Breithaupt’s (1865) ‘ko ¨lbingite’ the new mineral wilkinsonite from peralkaline, was but a mixture of aenigmatite and aegirine. silica-undersaturated trachyte of Warrumbungle Foerstner (1881) described the new triclinic volcano, New South Wales, Australia, which he mineral ‘cossyrite’ in volcanic rocks of the island named to honor J.F.G. Wilkinson for his work on Pantelleria, southern Italy (Cossyra in ancient volcanic rocks where the mineral was found. In times), and reported a chemical analysis, but not demonstrating the solid solution between the two including Ti. Groth (1883) noted that ‘cossyrite’ minerals, Hodges and Barker (1973) and Duggan and aenigmatite could be related, which Bro¨gger (1990) did not measure Fe3+ directly, but
843 E. S. GREW ET AL.
calculated it from stoichiometry. The structure of melt-rock (paralava) in the Powder River Basin, wilkinsonite is the most recent of sapphirine- Wyoming, as the new mineral dorrite in honor of group minerals to be refined (Burt et al., 2007). John A. Dorr, Jr., a professor at the University of Olsen and Fuchs (1968) described krinovite as Michigan. Negligible Ti content and dominance a monoclinic Na-Mg-Cr silicate from three ofFe3+ at octahedral sites were cited to octahedrite meteorites. The mineral was named distinguish dorrite from rho¨nite. On the basis of to honor E.L. Krinov for his work on meteorites. single-crystal data and absent a structure refine- Its relationship to aenigmatite was not demon- ment, Cosca et al. (1988) inferred that dorrite was strated until Merlino(1972) carried outa crystal- isostructural with aenigmatite and rho¨nite, and lographic study establishing its triclinic thus calculated dorrite composition assuming symmetry, and selected a triclinic cell to aenigmatite-group stoichiometry. Calculated conform to the Delaunay cell used by Kelsey Fe3+ occupies 66À73% of the octahedral sites in and McKie (1964) for aenigmatite. Bonaccorsi et type dorrite, and Al + Fe3+ exceeds Si at the al. (1989) solved the structure. tetrahedral sites. Refinements of SFCA (silico- ferrite of Ca and Al) and SFCAM (plus Mg) in the matrix of sinter ore show that these ferrites are Rh˛nite, dorrite, hÖgtuvaite, makarochkinite, welshite, isostructural with rho¨nite and compositionally serendibite closest to dorrite (Mumme, 1988, 2003; Soellner (1907) first recognized rho¨nite, which he Hamilton et al., 1989; Mumme et al., 1998; named for the Rho¨n Mountains of central Sugiyama et al., 2005). Germany, as a distinct triclinic mineral and Makarochkinite is named for Boris A. realized it was isomorphic with aenigmatite and Makarochkin, Russian chemist and mineralogist, ‘cossyrite’. Soellner found rho¨nite in alkaline whostudied the rare minerals fromthe Il’men basaltic rocks not only in the Rho¨n Mountains, but Mountains, southern Urals, near Miass, Russia alsoat several localitieselsewhere in Germany where the mineral was found in a pegmatite and in Bohemia plus one in Sweden. Walenta (Polyakov et al., 1986). These authors reported (1969) confirmed triclinic symmetry using single- that a proposal for makarochkinite was submitted crystal methods, and Merlino (1972) fixed the tothe CNMMN, but apparently there is norecord triclinic cell to conform to the Delaunay cell used of a vote; Shcherbakova et al. (2004) were by Kelsey and McKie (1964) for aenigmatite. skeptical that the materials ever reached the Bonaccorsi et al. (1990) first refined the structure. Commission. Høgtuvaite was first introduced as Although rho¨nite had a simpler history than a new species with an end-member formula 2+ aenigmatite, settling on a formula was compli- Ca4(Fe10Ti2)O4[Si10Be2]O36 from Be-rich ortho- cated by the greater compositional variation in gneiss at Høgtuva, a window of Proterozoic rocks rho¨nite. Fleischer (1936) suggested that aenigma- in the Caledonides, Nordland County, Norway tite and rho¨nite were related by the substitution Ca (Grauch et al. 1994; Burt 1994). The mineral was +Al> Na + Si by analogy with feldspar, but distinguished from rho¨nite because it contained Cameron et al. (1970) found that other substitu- sufficient Be tofill onetetrahedral site. In the tions were involved and noted the substantial absence of a structure refinement, Burt (1994) compositional gap between the two minerals. applied the vector method to define høgtuvaite. Fuchs (1971, 1978), Mason and Taylor (1982) Grauch et al. (1994) equated makarochkinite with and Simon et al. (1999) described rho¨nite høgtuvaite, but learned too late of the crystal containing about twice as much Ti as in other structure refinement of makarochkinite, which rho¨nite from calcium and aluminum rich inclu- gave 50% Be occupancy at two sites (Yakubovich sions in the Allende meteorite. Stoichiometry et al., 1990), toinclude it in their discussion. requires that a substantial portion of the Ti be Makarochkinite remained a synonym for trivalent. The presence of Ti3+ in a synthetic høgtuvaite until Grew et al. (2005) obtained analogue ‘baykovite’ is indicated by its distinctive CNMMN approval for its being distinct from absorption (Rudneva and Malysheva, 1960). høgtuvaite on the basis of new structural Structures of Allende rho¨nite and ‘baykovite’ refinements showing dominance of Ti at M7, were refined by Bonaccorsi et al. (1990) and whereas distinction from rho¨nite remained based Arakcheeva (1995), respectively. on stoichiometry, i.e. sufficient Be to occupy the Cosca et al. (1988) described a Ti-poor, Fe3+- equivalent of one tetrahedral site. The formulae rich analogue of rho¨nite from pyrometamorphic proposed by Grew et al. (2005) for høgtuvaite and
844 SAPPHIRINE AND SURINAMITE NOMENCLATURE
makarochkinite take into account the significant ferromagnesian aluminosilicate (de Roever et amounts of Al and Fe3+ present in both minerals al.,1976;Moore,1976).DeRoeveret al., (Table 1). (1981) and Grew (1981) discovered indepen- Ever since its first mention as an unnamed dently that Be is an essential constituent; the monoclinic mineral, Ca2(Mg,Fe)4SbSi4O12(OH)8, formula proposed by de Roever et al., (1981) with from the Fe-Mn skarn deposit of La˚ngban, 1 Be per 11 cations was confirmed by crystal Sweden (Moore, 1967), welshite has been one structure refinements (Moore and Araki, 1983; of the most intractable of the sapphirine group. Barbier et al., 2002). Surinamite being similar in After announcing the name (for Wilfred R. appearance tosapphirine is noaccident. As Welsh, teacher and amateur mineralogist) in mentioned above, both structure types belong to 1970 (Moore, 1970) and obtaining approval by a polysomatic series consisting of pyroxene and the CNMMN in 1973, Moore (1978) finally spinel modules. The sapphirine and surinamite published his description of welshite as a structure types are intergrown on a submicro- sapphirine-group mineral with the formula scopic scale in natural ferromagnesian alumino- 3+ 5+ Ca4Mg8Fe2 Sb2 O4[Si8Be4O36]. Taking advan- silicate (Christy and Putnis, 1988) and synthetic tage of Mo¨ssbauer spectroscopy and ion micro- Mg-Ga germanate (Barbier, 1996). probe analyses of Be, Grew et al. (2001) had a firmer basis for determining a formula and locating Fe in the structure. However, attempts Crystal structures torefine the crystal structure were foiledby Sapphirine-1A polysynthetic twinning and an eclectic composi- In the five polytypes of sapphirine that have been tion until J. Barbier successfully overcame these recognized (Merlino and Pasero, 1987; Christy difficulties to solve one welshite structure, and Putnis, 1988), order-disorder features are showing this mineral to be the only non- present (Merlinoand Zvyagin, 1998), but onlythe centrosymmetric sapphirine-group mineral and centrosymmetric triclinic sapphirine-1A (Fig. 1) allowing for the development of a satisfactory is topologically identical with minerals in the end-member formula (Grew et al., 2007). aenigmatite and rho¨nite subgroups (Table 2). Prior and Coomaraswamy (1903) first There are six tetrahedral sites of equal rank in described serendibite from a calc-silicate skarn chains parallel tothe a axis. Tetrahedral linkage is in Sri Lanka and named it for Serendib, the old 1 for the two tetrahedral wings (T5, T6), 3 for the Arabic designation for this island. Ye. N. Belova twochain tetrahedra ( T2, T3) linked tothe wings (in Pertsev and Nikitina, 1959) and Su¨sse (1968) and 2 for the other chain tetrahedra (T1, T4). carried out single-crystal work on serendibite and There are seven octahedral sites. Five (M1ÀM4, determined that it is triclinic, but Machin and M7) of these constitute the walls, which lie in the Su¨sse (1974) were the first torecognize its (011) plane and extend parallel tothe a axis, and relationship to the sapphirine group and adopted twoare outside the wall ( M8, M9). M7is the Delaunay cell used by Kelsey and McKie distinctive in that it shares the most edges (7) (1964) for aenigmatite. Buerger and with adjacent polyhedra. The main difference Venkatakrishnan (1974) refined the structure, between sapphirine-1A and minerals in the but only to R = 7.1%. They reported B > Al aenigmatite and rho¨nite subgroups is that the M5 and Mg > Ca substitutions, anomalous features and M6 sites (corresponding to M8 and M9 in the that prompted Van Derveer et al. (1993) torefine other subgroups) in sapphirine-1A are 6-coordi- the structures of three serendibite samples nated. These octahedra do not cross-link the differing in Fe content to weighted R = octahedral walls, but can be considered part of 2.8À3.3 wt.%, and thereby established Si > B these walls (Moore, 1969). The oxygen anions are substitution at the T1 and T4 sites and Ca > Na cubic close-packed in sapphirine, whereas Ca and substitution at the M8 and M9 sites. Na disrupt close packing in the other subgroups. In general, cation ordering in the sapphirine group is primarily driven by charge ordering and Surinamite should be similar given the similar topologies of Surinamite was first described as sapphirine in a the structures. However, the degree of ordering metamorphic rock from the Bakhuis Mountains, will depend on the chemical composition of a Surinam (de Roever, 1973), but chemical analyses particular phase through the charges of the cations andX-raystudyshowedittobeanew occupying the various M and T sites. In
845 E. S. GREW ET AL.
FIG. 1. Crystal structure of sapphirine-1A. Numbering of sites corresponds to column 1 of Table 2. Oriented to facilitate comparison of site numbering with that in the makarochkinite structure shown in Fig. 3. Green tetrahedra: Si = Al or Si > Al; yellow tetrahedra: Al or Al > Si.
sapphirine-1A there is a moderately high degree more highly charged cation, e.g. Ti in aenigmatite of cation order at both the M and the T sites. and Cr in krinovite, and M3ÀM6 sites by divalent cations. Cr also occupies the M1 and M2 sites in krinovite. The new refinement of aenigmatite Sapphirine-2M and khmaralite (Grew et al., 2008) gives greater cation order at The two monoclinic minerals in the sapphirine M1ÀM7 sites than earlier reported (Cannillo et subgroup are not topologically identical to al., 1971), viz. 100% (vs. 59%) of Ti at M7 and sapphirine-1A, but differ in the number of M subordinate Mg substitutes for Fe only at sites: the twonon-wall M sites in the triclinic M3ÀM6. Fe3+ is dominant at the M1, M2 and structure are equivalent in sapphirine-2M. M7 sites in wilkinsonite (Burt et al., 2007). Khmaralite differs from sapphirine-2M in having a supercell due to doubling along the a axis; it has Rh˛nite, rh˛nite (Allende), hÖgtuvaite, makarochkinite, 12 T sites and 16 M sites (Fig. 2; Table 3). This welshite response to Be incorporation differs from that in the rho¨nite subgroup, and allows a maximum of Compositions of the M1ÀM7 and T sites are more only 2 Be per 28 cations. complex and cation disorder greater in the five rho¨nite subgroup minerals for which structure refinements are known (Fig. 3; Table 2). M8 and Aenigmatite, wilkinsonite, krinovite M9 are dominantly Ca and the distinction between The compositions of the aenigmatite subgroup the seven shorter bonds and one longer bond is minerals whose structures have been refined commonly more marked. Be and B are concen- (Tables 2, 3) are relatively highly ordered, with trated on the most polymerized T sites (T1, T4). Ti all the T sites occupied by Si; M7 occupied by the is ordered at M7 in høgtuvaite, makarochkinite
846 SAPPHIRINE AND SURINAMITE NOMENCLATURE
TABLE 2. Simplified occupancies in minerals of the aenigmatite subgroup, rho¨nite subgroup (except dorrite) and sapphirine-1A based on crystal structure refinements.
Spr-1A Aen Wlk Krin Rho¨ Rho¨-All Høg Mkr Welshite* Srd S.G. P1¯ P1¯ P1¯ P1¯ P1¯ P1¯ P1¯ P1¯ P1 P1¯
T3** Si = Al T1** Si Si Si Si = Al Si = Al Si = Be Si = Be Si/Be B 5 Si T4Al>SiT2 Si Si Si Si = Al Si = Al Si Si Si/Be Si T1Al T3 Si Si Si Si = Al Si = Al Si > Al Si = Al Be = Al/Si Al T2** Si > Al T4** Si Si Si Si = Al Si = Al Si = Be Si = Be Be/Si B T6Al>SiT5 Si Si Si Si = Al Al Si Si Al = Fe/Si Si T5Al T6 Si Si Si Si = Al Al Si Si Si/Al = Fe Si M8** Al M1** Fe Fe Cr Mg Mg = Ti Fe Fe Mg Al M9** Al M2** Fe Fe Cr Mg Mg = Ti Fe Fe Mg Al M1Al M3 Fe Fe Mg Mg Mg = Ti Fe Fe Mg/Sb Al or Mg M2Al M4 Fe Fe Mg Mg Mg = Ti Fe Fe Mg/Sb Al M4Mg M5 Fe Fe Mg Mg Mg Fe Fe Mg/Mg Mg M3 Mg M6 Fe Fe Mg Mg Mg Fe Fe Mg/Mg Mg M7Al M7 Ti Fe Cr Ti Mg = Ti Fe Ti Sb/Mg Al M5Mg M8 Na Na Na Ca Ca Ca Ca Ca/Ca Ca M6Mg M9 Na Na Na Ca Ca Ca Ca Ca/Ca Ca
Sources given in Table 1. Dorrite is not included because the structure has not been refined. S.G. À space group. The site labelling (first column) applies only to sapphirine-1A (the third column gives the correspondence for the other minerals). Equal sign (=) indicates approximately equal occupancy by the given constituents. * For welshite, all sites are split except for non-wall octahedra M1 and M2, so occupancies for both sites are given, separated by a forward slash, with the A-labelled site second. ** Indicates the most polymerized T sites and non-wall octahedral sites. Abbreviations: Spr-1A À sapphirine-1A, Aen À aenigmatite, Wlk À wilkinsonite, Krin À krinovite, Rho¨ À rho¨nite, Rho¨- All À rho¨nite from the Allende meteorite, Høg À høgtuvaite, Mkr À makarochkinite, Srd À serendibite.
and rho¨nite, whereas Mg, Fe2+ and Fe3+ are sites with the most shared edges (M7, M7A). disordered over the M1ÀM6 sites. The Allende Nonetheless, there is considerable cation order, rho¨nite differs in that Ti (including Ti3+ as well as which allows for incorporation of more Be than in Ti4+) and Mg are disordered over the M1ÀM4 and other minerals of the group, up to 3.46 vs. the M7 sites, leaving M5 and M6 dominated by Mg. maximum of 2.1 Be per 28 cations (høgtuvaite) In contrast to other minerals in the aenigmatite and still avoids BeÀOÀBe bridges. and rho¨nite subgroups, rho¨nite has at least two polytypes. Bonaccorsi et al. (1990) gave HRTEM Surinamite evidence for an 8-layer polytype of rho¨nite (rho¨nite-8A) that is 200 A˚ wide in a crystal from Surinamite (Fig. 5) is highly ordered compared to Scharnhausen, Germany. sapphirine and khmaralite. As in sapphirine, the Welshite is unique among minerals in the oxygen anions are cubic close-packed. Only one sapphirine group in being non-centrosymmetric polytype (1M) has been reported for natural with 12 T sites and 16 M sites, the increase surinamite, which has space group P2/n, although resulting from the loss of the symmetry center a different polytype (2M) with space group C2/c (Fig. 4). The first successful crystal structure is realized in a synthetic Ga-Ge analogue of refinement alsoresulted in a new end-member surinamite (Barbier, 1996, 1998). formula (Table 1), which differs significantly from the one proposed by Moore (1978) and 3+ Compositional variations given in standard references, Ca4(Mg8Sb2Fe2 )O4 [Si8Be4O36] (e.g. Strunz and Nickel, 2001). Be is Sapphirine-1A and -2M, khmaralite not restricted to the most polymerized T sites (T1, The principal compositional variations in Be- and T1A, T4, T4A) sites nor is Sb restricted to the M B-free sapphirine include the homovalent Fe >
847 E. S. GREW ET AL.
FIG. 2. Crystal structure of khmaralite. Numbering of sites corresponds to column 1 of Table 3 (cf. column 1, Table 2). Oriented to facilitate comparison of site numbering with that in the makarochkinite structure shown in Fig. 3. Green tetrahedra: Si, Si >> Be > Al or Si > Al; yellow tetrahedra: Al or Al > Si; orange tetrahedra: Be = Si + Al or Be > Al.
Mg, Fe > Al, and Cr > Al substitutions, and the scopy are 0.85 per 28 cations in Fe2+-bearing heterovalent (Mg, Fe) + Si > 2(Al, Fe, Cr) sapphirine (Wilson Lake, Canada, Burns and (Tschermaks) substitution (e.g. Deer et al., 1978; Solberg, 1990) and 1.00 per 28 cations in a Higgins et al., 1979; Christy, 1989; Podlesskii et sapphirine lacking Fe2+ (Mautia Hill, Tanzania, al., 2008), but Fe- and Cr-dominant analogues have McKie, 1963; Bancroft et al., 1968). The highest not been reported in nature, nor has a Fe-dominant Fe3+ contents obtained by other methods are analogue been synthesized. Total Fe (as FeO) is in 1.93 Fe3+ per 28 cations that Sahama et al. the range 0.05À16.55 wt.% (minimum and (1974) determined by wet chemistry in a sapphirine maximum from Mangari area, Kenya and from Labwor, Uganda, and 1.89 Fe3+ per 28 cations Vizianagaram, India, by Mercier et al., 1999 and that Gnos and Kurz (1994) calculated in a Kamineni and Rao, 1988, respectively), but in most sapphirine from the Semail ophiolite in the United cases, both Fe3+ and Fe2+ are present, and their Arab Emirates. However, these contents exceed the proportions are generally calculated from stoichio- maximum that Steffen et al. (1984) were able to metry in the absence of a direct determination, e.g. incorporate in synthetic Mg-sapphirine: 1.4 Fe3+ by Mo¨ssbauer spectroscopy. Up to 2.77 Fe2+ per 28 per 28 cations. The presence of Fe2+ could favour cations and Fe2+/(Fe2+ +Mg)=0.36hasbeen incorporation of Fe3+;nonetheless,Fe3+ contents calculated from stoichiometry (Vizianagaram, exceeding 1.4 need confirmation. India, Kamineni and Rao, 1988). Maximum Fe3+ Using Mo¨ssbauer spectroscopy, Bancroft et al. contents directly measured by Mo¨ssbauer spectro- (1968) and Steffen et al. (1984) located Fe3+ at
848 SAPPHIRINE AND SURINAMITE NOMENCLATURE
TABLE 3. Simplified occupancies in the monoclinic minerals sapphirine-2M and khmaralite.
Sapphirine-2M Khmaralite Equivalent site* S.G. P21/a P21/cP1¯ T3** Si = Al Si >> Be > Al T1** T9** À Be > Al T1** T4AlSi>Al T2 T10 À Al T2 T1AlAl>Si T3 T7 À Al > Si T3 T2** Si Be = Si + Al T4** T8** À Si T4** T6 Al > Si Al > Si T5 T12 À Si T5 T5AlAl>Si T6 T11 À Al T6 M8** Al Al M1**, M2** M16** À Al M1AlAl M3 M9 À Al > Mg M3 M2AlAl M4 M10 À Al > Mg M4 M4MgMg M5 M12 À Mg M5 M3 Al = Mg Al M6 M11 À Mg > Al M6 M7AlAl M7 M15 À Al M7 M5MgMg>Al M8 M13 À Mg M8 M6MgMg M9 M14 À Mg M9
Sources given in Table 1. S.G. À space group. Equal sign (=) indicates approximately equal occupancy by the given constituents. * In the other subgroups (Table 2). ** Indicates the most polymerized T sites and non-wall octahedral sites.
tetrahedral sites, whereas Burns and Solberg Mg4(Mg3.8Cr6.7Al1.4)O4[Si4.1Al7.9O36], can be (1990) concluded that Fe3+ occupies octahedral written if all Cr3+ remains octahedrally coordinated sites, which is consistent with Fe3+ occupancy at this temperature. determined by single-crystal refinement in The Tschermak substitution is extensive in sapphirine-1A from Wilson Lake, Canada sapphirine. Si ranges from 1.71 to 4.49 per (Merlino, 1980). Nonetheless, Fe3+ occupancy in 28 cations in Be poor compositions; that is, a sapphirine remains an open question. few compositions extend beyond the usual limits The maximum Cr content is 1.42 per 28 cations of Si = 2 and Si = 4 given for sapphirine, which (7.52 wt.% Cr2O3, Fiskenæsset region, Greenland, correspond to the 2:2:1 and 3:5:1 compositions in 3+ 3+ vi Friend, 1982); the corresponding Cr /(Cr + Al) terms of the (Mg,Fe,Mn)O:(Al,Fe,Cr,V)2O3:SiO2 ratiois 0.15, i.e. 15% ofa Cr end-member if Cr ratio (Fig. 6). The great majority of compositions occupies only octahedral sites as suggested by the are closer to the 7:9:3 composition, which is given large octahedral site preference energy for Cr3+ as the end-member in Table 1. Preference for this (Navrotsky, 1975; Burns, 1993). Brigida et al. ratio is not surprising given the considerable (2007) synthesized at 1340ºC and 1 bar a sapphirine octahedral ordering in sapphirine, i.e. Mg at M4, for which a formula with 83% of a Cr end-member, M5, and M6, viAl at M1, M2, M7, M8 and M9,
849 E. S. GREW ET AL.
FIG. 3. Crystal structure of makarochkinite, which is representative of the structures of the centrosymmetric triclinic Na and Ca aenigmatite subgroup. Numbering of sites corresponds to column 3 of Table 2 (cf. column 4, Table 3). Green tetrahedra: Si; yellow tetrahedra: Si = Al; orange tetrahedra: Be = Si; lavender octahedra: Ti.
FIG. 4. Crystal structure of welshite, which is uniquely non-centrosymmetric Ca aenigmatite subgroup mineral. Numbering of sites corresponds to column 3 of Table 2, but sites are split (lettered vs. unlettered) due toabsence of symmetry centre. Green tetrahedra: Si; yellow tetrahedra: Al = Fe; orange tetrahedra: Be or Be = Al; lavender octahedra: Sb.
850 SAPPHIRINE AND SURINAMITE NOMENCLATURE
FIG. 5. Crystal structure of surinamite. Green tetrahedra: Si; yellow tetrahedra: Al; orange tetrahedra: Be. with M3 generally split (Moore, 1969; Higgins could also be trivalent in part (Ti3+-bearing and Ribbe, 1979; Merlino, 1980), summing to rho¨nite is alsofromAllende, but in Ca-Al-rich ~7 Mg and ~9 viAl per 28 cations (Tables 2, 3). inclusions). Assuming Ti is trivalent improves The tetrahedra are less well ordered (at least in the stoichiometry of the two compositions reported long range); the ratio of ~3 Si to ~ 9 ivAl in typical by Sheng et al. (1991). sapphirine is dictated by charge balance. Beryllium is incorporated in sapphirine through Calcium is generally a minor component of the substitution Be + Si > 2Al, which relates the sapphirine, rarely exceeding 0.2 wt.% CaO end-members for sapphirine and khmaralite given (Christy, 1989). However, Grew et al. (1992) in Table 1 (Grew, 1981; Barbier et al., 1999, 2002; reported B-rich sapphirine containing up to Christy et al., 2002; Grew et al., 2006). There 5.4 wt.% CaO, which was attributed to35% appears an unbroken solid solution between Be- serendibite in solid solution. free sapphirine and khmaralite containing 1.57 Be Other constituents reported in sapphirine in per 28 cations, the maximum Be in natural amounts exceeding 1 wt.% oxide are MnO (to khmaralite (Fig. 6). The superstructure with 1.16 wt.%, Madurai Block, south India; Tateishi doubled chain periodicity characteristic of khmar- et al., 2004) and TiO2 (to1.25 wt.% in terrestrial alite appears at about 1 Be per 28 cations (Grew et sapphirine, Vestfold Hills, Antarctica, Harley and al., 2000). The octahedral composition of khmar- Christy, 1995; and 1.60À2.30 wt.% in sapphirine alite is roughly 7 (Mg, Fe2+)and9(Al,Fe3+) in plagioclase-olivine inclusions in the Allende (Table 3) as a consequence of the marked ordering meteorite, Sheng et al. 1991). Stoichiometric at octahedral sites, an ordering very similar to that calculation of compositions of ‘fassaite’ in other of sapphirine (Barbier et al., 1999). Moreover, plagioclase-olivine inclusions gave Ti3+ = sapphirine and khmaralite having intermediate Be 60À80% of total Ti (Sheng et al., 1991), contents plot close to a line joining the end- suggesting that the Ti in the Allende sapphirine member sapphirine and khmaralite compositions
851 E. S. GREW ET AL.
FIG. 6. Composition of sapphirine in terms of mole proportions SiO2, (Mg, Fe, Mn, Ni)O and (Al,Fe,Cr,V,Ti)2O3. Al-analogue of sapphirine refers to a distinct species, yet unnamed, in which Si < 2 per 28 cations (Table 4). BeSiAlÀ2 and MgSiAlÀ2 refer tothe substitutionsBe + Si > 2Al and Mg + Si > 2Al, respectively. Analyses of sapphirine selected to show only relatively Si-rich compositions (Dawson et al., 1997; Gnos and Kurz, 1994; Grew et al., 1994; Harley and Christy, 1995; Owen et al., 1988; Sajeev and Osanai, 2004; Sheng et al., 1991; Sills et al., 1983; Simon and Chopin, 2001) and Al-rich ‘peraluminous’ compositions (Godard and Mabit, 1998; Grew et al., 1988; Harley and Christy, 1995; Liati and Seidel, 1994; Nijland et al., 1998; Sabau et al., 2002; Schreyer and Abraham, 1975; Warren and Hensen, 1987); most sapphirine compositions are intermediate and have not been plotted. Ti is assumed to be trivalent only in the Allende sapphirine; in all others, Ti is assumed to be tetravalent. Be = 1 atom per 28 cations serves as the distinction between khmaralite and beryllian sapphirine. The plot includes all available compositions of khmaralite and Be-rich beryllian sapphirine (BeO > 1 wt.%) (Grew, 1981; Barbier et al., 1999; Grew et al., 2000 and unpublished data), but only selected compositions for beryllian sapphirine with Be contents between 1 and 0.2 wt.% BeO (Grew et al., 2006).
(Fig. 6). Christy et al. (2002) synthesizied only found at Johnsburg, New York, USA beryllian sapphirine in the MgO-BeO-Al2O3- (Grew et al., 1992), contains significantly more SiO2-H2O system, but none had the superstructure B. A formula for the averaged composition with characteristic of khmaralite. No more than 2 Be per 2.08 wt.% B2O3 is Mg3.6Ca0.4(Mg2.8Fe0.1Al9)O4 28 cations could be incorporated, and this amount [Si3.2B0.8Be0.1Al7.9O36], but the sapphirine is very only in starting compositions corresponding to the heterogeneous compositionally. Examination by 2:2:1 composition plus 0.5 BeSiAlÀ2. Tworuns of TEM led Grew et al. (1992) toconcludethat the this composition gave single-product sapphirine, heterogeneous material is structurally a single- implying its composition was Mg4(Mg4Al8)O4 phase triclinic Ca-B sapphirine; this phase [Si6Be2Al4O36], but this was not confirmed by appears to be a solid solution of serendibite and direct analysis. B-bearing sapphirine that subsequently exsolved Ca-poor sapphirine associated with prismatine Ca-richer material. The averaged composition at several localities incorporates up to 0.85 wt.% (1.47 wt.% CaO, 2.08 wt.% B2O3) corresponds B2O3, corresponding to 0.35 B per 28 cations roughly to 10% serendibite and 25% (Grew, 1986; Grew et al., 1990, 1991b). B- Mg4(Mg3Al9)O4[Si3B2Al7O36] in solid solution. bearing sapphirine compositions are somewhat richer in Si than the 7:9:3 composition; the B Aenigmatite, wilkinsonite, krinovite contents correspond to ~17% of a B analogue to the 7:9:3 composition, Mg4(Mg3Al9)O4 Aenigmatite and wilkinsonite constitute a contin- [Si3B2Al7O36]. Ca-bearing sapphirine, todate uous solid solution series linked predominantly by
852 SAPPHIRINE AND SURINAMITE NOMENCLATURE
TABLE 4. Classification scheme for the sapphirine supergroup.
3 Polysome Largest M Most shared Q TXMg Mineral or (group) (subgroup) edges possible mineral
Sapphirine M5, M6 M7 T2, T3 Sapphirine
M8, M9 M7 T1, T4 Aenigmatite
Columns are 1 À Group name and polysome symbol; 2 À Subgroup name and occupant of two or three largest M sites, 3 À Occupants of M site with most shared edges, 4 À Occupants of most polymerized T sites. 5 À XMg = atomic Mg/(Mg + Fe2+) at other M sites. Names of minerals approved by the CNMNC (CNMMN) are in capital letters. 1Total Be or B occupancy at the two T sites considered together for the end-member composition given in Table 1. 2Khmaralite contains two sapphirine sub-cells (M1À8, T1À6 and M9À16, T7À12). Be > 0.5 at each of T2 and T9. 3Ti3+-bearing Mg-analogue of rho¨nite. 4 Welshite has P1 symmetry sothat the T1–T6 and M3–M9 sites are doubled. Be = 1 at T1A and T4, contributing 2 Be to the end-member formula (Table 1) from these sites; Sb = 1 at M7 and Mg = 1 at M7A.
the substitution Fe2+ +Ti> 2Fe3+ (Hodges and respectively, and is the richest in Mn yet reported. Barker, 1973; Larsen, 1977; Duggan, 1990). In most cases, Mg contents are lower, mostly Homovalent substitutions, notably Mn or Mg for <1 wt.% MgO, but with two notable exceptions. Fe2+ and Al for Fe3+, are limited in extent. For Price et al. (1985) and Price (pers. comm.) example, Ridolfi et al. (2006) reported an reported 8.88À10.61 wt.% MgO, corresponding aenigmatite in one sample of a silica-saturated to3.53 À4.21 Mg per 28 cations and peralkaline syenite autolith, from Kilombe Mg/(Mg+Fe2+) = 0.43À0.48 in aenigmatite from volcano, Kenya, with 5.98À7.93 wt.% MnO, nepheline syenite on Mount Kenya. Aenigmatite which corresponds to 1.428 and 1.894 Mn per found in an albite clast in the Kaidun meteorite, a 28 cations and Mn/(Mn + Fe2+) = 0.15 and 0.20, breccia, contains 3.64À6.81 wt.% MgO, corre-
853 E. S. GREW ET AL. sponding to 1.50À2.71 Mg per 28 cations and written more specifically as M7Ti + M1,M2Fe2+ > Mg/(Mg+Fe2+) = 0.16À0.29, Ivanov et al., 2003; M7Fe3+ + M1,M2Fe3+, which is probably the most Zolensky and Ivanov, 2003). Bischoff et al. important substitution relating the two minerals. (1993) reported 3.7 wt.% MgO in a phase in an Substitutions 3 and 4 can explain why analyses alkali-granite clast in meteorite Adzhi-Bogdo; this from other areas as well as Ilı´maussaq give more phase is probably aenigmatite (Ivanov et al., Fe3+ than predicted by substitution 1 (e.g. 2003). With Mg/(Mg+Fe2+) = 0.06 (Ivanov et al. Vesterøya, Norway, Grew et al., 2008) and why 2003; Zolensky and Ivanov, 2003), wilkinsonite Al > Ca. Substitution 2 links end-member associated with aenigmatite in the Kaidun aenigmatite with our suggested end-member meteorite is more magnesian than any terrestrial composition for the Fe2+ analogue of rho¨nite material with the exception of wilkinsonite (Table 1), whereas substitutions 2 and 3 working containing 5.50 wt.% MgO, i.e. Mg/(Mg + Fe2+) in tandem at a 2:1 ratio, together with Mg > Fe2+, = 0.53, from a syenitic ejectum, Wonchi volcano, link end-member aenigmatite with the composi- Ethiopia (Gaeta and Mottana, 1991). In contrast to tion given for rho¨nite in Table 1. The trend at the magnesian aenigmatite from Mount Kenya, in greater Ca contents (Al/Ca = 1.5, Fig. 8b)is which divalent cations total 8.5À9.0 per consistent with the latter, i.e. over 20% solid 28 cations, close to the ideal 10, divalent cations solution of a Fe2+-dominant analogue of the total only 5.1 in the Wonchi wilkinsonite, rho¨nite composition given in Table 1. significantly less than the 8 per 28 cations in The new structure refinement and Mo¨ssbauer ideal wilkinsonite. data (Grew et al., 2008) confirm earlier sugges- Aenigmatite and wilkinsonite deviate to some tions based on Mo¨ssbauer spectroscopy (Choi, degree from ideal stoichiometry. Ti exceeds 1983; Choi and Burns, 1983; Burns and Solberg, 2 atoms per 28 cations in some samples, and 1990) that tetrahedral Fe3+ is present in most analyses give Fe3+ in excess of that expected aenigmatite. The sum Si + Al is significantly from Fe2+ +Ti> 2Fe3+ (Fig. 7a). Non- less than 12 in other aenigmatite samples stoichiometry also results from incorporation of (Fig. 7b), and this deficit at tetrahedral sites is constituents other than Fe, Ti, Mg, Mn, Na and Si. best explained by tetrahedral Fe3+ in the absence The most important of these are Ca and Al, e.g. of other tetrahedrally coordinated cations such as Ca content ranges from negligible to nearly Be and B. Thus, substitution 4, which introduces 1 atom per 28 cations, i.e. ~25% substitution of tetrahedral Fe3+, undoubtedly plays a role, albeit Na by Ca (Fig. 8). In most analyses the sum of Na minor, in aenigmatite crystal chemistry. + Ca + K ranges from 4.0 to 4.2 atoms, i.e. Nb, Zr, Sn and Zn are reported in amounts up to somewhat in excess of stoichiometry with more 1 wt.% oxide, sometimes more (e.g. 3.72 wt.% scatter at low Ca content. This excess in electron Nb2O5 in wilkinsonite, corresponding to 0.49 Nb microprobe analyses could be due to improper per 28 cations; Duggan, 1990). Other elements, standardization of Na as Larsen (1977) suggested. notably Li (to 0.06 wt.% Li2O, corresponding to Aluminum content ranges from 1.5 to 6 times Ca 0.07 Li per 28 cations, Howie and Walsh, 1981; content, and is close to 1.5 in Ca-rich analyses Raade and Larsen, 1980; A˚ sheim et al., 2008), (Fig. 8b). K2O contents greater than 0.2 wt.% could also be significant; but relatively few papers (>0.07 K per 28 cations) are rarely reported, and report analyses of these minor constituents. only in wet chemical analyses with one exception A˚ sheim et al. (2008) reported other trace (0.75 wt.% or 0.28 K per 28 cations, Wonchi element contents in aenigmatite from the Larvik wilkinsonite, Gaeta and Mottana, 1991). plutonic complex, Norway, including 28À31 ppm Larsen (1977) invoked the following four Be and 11À92 ppm B (cf. ~20 ppm Be, Lovozero, coupled substitutions to account for compositional Vlasov et al., 1966). Because the ferric/ferrous variation in aenigmatite from the Ilı´maussaq ratioin mostsamples is calculated from complex, Greenland: stoichiometry, ignoring Nb, Zr, Sn, Zn and Li 3+ vi vi 2+ vi 3+ can lead toerrorsin calculating Fe content, Ti + Fe >2 Fe (1) Ca + ivAl > Na + ivSi (2) above and beyond errors inherent in the calcula- viFe2+ + ivSi > viFe3+ + ivAl (3) tion itself. viFe2+ + ivSi > viFe3+ + ivFe3+ (4) Only one analysis of krinovite has been reported (Olsen and Fuchs, 1968). Its composition Taking into account the refinement of wilk- approaches that of the end-member with 5% insonite (Burt et al., 2007), substitution 1 can be substitution of Mg by Fe (Bonaccorsi et al.,
854 SAPPHIRINE AND SURINAMITE NOMENCLATURE
2+ 3+ FIG. 7. Compositional variations of aenigmatite (Aen) and wilkinsonite as functions of Ti and Si. (TiFe )(Fe )À2 in (a) indicates the substitution viTi + viFe2+ > 2 viFe3+ relating aenigmatite and wilkinsonite. Vesterøya Aen refers to electron microprobe data on a sample from Vesterøya, Norway from which a crystal was used to newly refine the structure (Fe3+/SFe calculated from chemical data and measured by Mo¨ssbauer spectroscopy, Grew et al., 2008). We calculated Fe3+/Fe2+ ratio in all the other analyses by assuming 28 cations and 40 oxygens whether or not Fe3+ had been measured directly in wet chemical analyses or calculated by the original authors from electron microprobe analyses. Sources of other data: Abbott (1967); Avanzinelli et al. (2004); Barker and Hodges (1977); Barker (unpublished data); Birkett et al. (1996); Bischoff et al. (1993); Bohrson and Reid (1997); Borley (1976); Bryan (1969); Bryan and Stevens (1973); Bulakh (1997); Carmichael (1962); Curtis and Currie, 1981; Dawson (1997); Downs (2006); Duggan (1990); Ewart et al. (1968); Farges et al. (1994); Ferguson (1978); Gaeta and Mottana (1991); Gibb and Henderson (1996); Grapes et al. (1979); Henderson et al. (1989); Howie and Walsh (1981); Ike (1985); Ivanov et al. (2003); Jones (1984); Jørgensen (1987); Kelsey and McKie (1964); Krivdik and Tkachuk (1988); Larsen (1977); Lindsley and Haggerty (1970); Mahood and Stimac (1990), Marks and Markl (2003); Marsh (1975); Mitrofanov and Afanas’yeva (1966); Nash et al. (1969); Nicholls and Carmichael (1969); Nkoumbou et al. (1995); Platt and Woolley (1986); Powell (1978); Price (personal communication, 2007); Price et al. (1985); Ren et al. (2006); Stolz (1986); Velde (1978); Vlasov et al. (1966); White et al. (2005); Yagi and Souther (1974); Zies (1966).
855 E. S. GREW ET AL.
FIG. 8. Compositional variations of aenigmatite (Aen) and wilkinsonite as a function of Ca. Arrows in (b) point to the 2+ 2+ end-member composition of rho¨nite plus Fe Mg–1 and to the suggested end-member composition of the Fe analogue of rho¨nite (Table 1). Vesterøya Aen refers to electron microprobe data on a sample from Vesterøya, Norway from which a crystal was used to newly refine the structure (Grew et al., 2008). Wilkinsonite (Mg) refers to the unnamed Mg-dominant analogue reported by Gaeta and Mottana (1991). Other sources are given in the caption toFig. 7.
1989); other minor constituents are Al2O3 nents (e.g. Cosca et al., 1988; Kunzmann, 1989, (0.6 wt.%), TiO2 (0.5 wt.%), CaO and MnO 1999). There is noevidence fora miscibility gap (0.1 wt.% each). between dorrite and rho¨nite (Fig. 9) as Cosca et al. (1988) suggested on the basis of the many fewer compositions available to them. Total Ti Rh˛nite, dorrite, makarochkinite, hÖgtuvaite ranges from nearly negligible in dorrite to over The Be-poor ferromagnesian silicates rho¨nite 4.5 atoms per 28 cations in Allende rho¨nite. (including the Fe2+-dominant analogue and However, there is a major change at Ti & 3.1 rho¨nite in Ca-Al-rich inclusions in the Allende atoms. For Ti < 3.1, with one exception (see meteorite) and dorrite appear to constitute a below), formula calculation using stoichiometry complex solid solution involving several compo- and assuming all Ti is Ti4+ gives Fe3+, whereas
856 SAPPHIRINE AND SURINAMITE NOMENCLATURE
2+ 3+ FIG. 9. Si and Ti contents of dorrite, rho¨nite and its Fe analogue and its Ti -bearing Mg analogue (Allende), høgtuvaite and makarochkinite (modelled on Kunzmann, 1999, Fig. 7 and Grew et al., 2005, Fig. 5). Except for analyses of makarochkinite and høgtuvaite for which Mo¨ssbauer data were available (Grauch et al., 1994; Grew et al., 2005), we calculated Fe3+/Fe2+ ratio by assuming 28 cations and 40 oxygens (unless 28 cations gave all Fe as Fe3+) whether or not Fe3+ had been measured directly in wet chemical analyses or calculated by the original authors from electron microprobe analyses. End-member compositions are given in Table 1 (compositions for makarochkinite and Fe2+ analogue of rho¨nite are superimposed, and thus the plotted squares are slightly displaced from the ideal value). Vertical arrow shows the effect of the substitution Be + Si > 2Al, which relates høgtuvaite and makarochkinite to rho¨nite and its unnamed Fe2+ analogue. The vertical lines indicate species boundaries for the 3+ names in bold. Included with dorrite (diamonds) are the Fe -rich ‘melilite’ of Foit et al. (1987), ‘mineral X1’of Havette et al. (1982) and several analyses given as ‘rho¨nite’ by Kunzmann (1989), Rondorf (1989) and Johnston and Stout, 1984). Two compositions approach a Fe-analogue: one from Luna 24 regolith (lunar, Treiman, 2008), and another from angrite NWA 4590, a meteorite (angrite, Kuehner and Irving, 2007). Sources of the other compositional data: Alletti et al. (2005); Boivin (1980); Bonaccorsi et al. (1990); Brooks et al. (1979); Cameron et al. (1970); Corsaro et al. (2007). Cosca et al. (1988); Downes et al. (1995); Fodor and Hanan (2000); Fuchs (1971, 1978); Gamble and Kyle (1987); Grapes et al. (2003); Grew et al. (2005); Gru¨nhagen and Seck (1972); Hurai et al (2007); Jannot et al. (2005); Johnston and Stout (1985); Kunzmann (1989), Kyle and Price (1975); Magonthier and Velde (1976); Mao and Bell (1974); Mason and Taylor (1982); Ne´dli and To´th (2003); Nishio et al. (1985); Olsson (1983); Polyakov et al. (1986); Prestvik et al. (1999); Simon et al. (1999); Soellner (1907); Timina et al. (2006); Warren et al. (2006).
for Ti > 3.1, this stoichiometric calculation gives Total Ca + Na + K (K is much subordinate to negative Fe3+. If we assume that all Fe is Fe2+, Na) sum close to 4 atoms per 28 cations in rho¨nite then compositions with Ti > 3.1 give both Ti4+ and dorrite (except for 5 of 8 compositions in the and Ti3+, and the latter increases with increasing type dorrite sample), with up to nearly 40% total Ti. The only natural phase containing more substitution of Ca by Na+K (Fig. 10). Corsaro et than 3.1 Ti and calculated Ti3+ is rho¨nite from the al. (2007) reported up to 1.3 wt.% SrO (0.21 Sr Allende meteorite. ‘Baykovite’ (‘baikovite’), a per 28 cations). Al decreases in a 1:1 ratio with Ca component of Si-Ti slag, is an isostructural phase (Fig. 11), which is not consistent with solid containing 5.82À6.01 Ti, of which 3.63À3.76 is solution towards aenigmatite (cf. Fig. 8b). Most Ti3+ per 28 cations (Rudneva and Malysheva, dorrite contains relatively little Na + K, but Ca > 4 1960; Arakcheeva, 1995); an average formula atoms per 28 cations, implying Ca substitution at from the reported data is Ca4(Ca0.3Mg5.55Al0.24 sites other than M8 and M9; up to0.9 excess Ca 3+ 4+ Ti3.69Ti2.23)O4[Si3.6Al8.4O36]. per 28 cations is ordered at M5 in SFCA and
857 E. S. GREW ET AL.
2+ 3+ FIG. 10. Na and Ca contents of dorrite, rho¨nite and its Fe analogue and its Ti -bearing Mg analogue, høgtuvaite and makarochkinite. Allende rho¨nite containing 4.86 Ca (Fuchs, 1971) is not plotted. Ca content includes Sr in the 7 analyses reported by Corsaro et al. (2007). Other information and sources are given in the caption of Fig. 9.
SFCAM (Hamilton et al., 1989, Mumme et al., Eifel, Germany), a trend consistent with the 1998; Sugiyama et al., 2005) and 0.29 Ca at M5 substitution (Na, K) + Si > Ca + Al (e.g. and M6 in ‘baykovite’ (Arakcheeva, 1995). Al Kunzmann, 1989, 1999; this paper, Fig. 11). In increases with Ca in rho¨nite and some dorrite (i.e. dorrite from the type locality (Cosca et al., 1988), from Kauai, Hawaii, USA and Nickenicher-Sattel, Buffalo, Wyoming (Foit et al., 1987) and from
2+ FIG. 11. Al and Ca contents of dorrite, rho¨nite and its Fe -dominant analogue, høgtuvaite and makarochkinite. Unfilled squares correspond to end-members (Table 1). Arrow shows the effect of the substitution Be + Si > 2Al. Ca content includes Sr in the 7 analyses reported by Corsaro et al. (2007). Other information and sources are given in the caption of Fig. 9.
858 SAPPHIRINE AND SURINAMITE NOMENCLATURE
Reunion Island (Havette et al., 1982), Al does not which are related tothe average Si and Al contents vary with Ca. In many of these compositions, Al ofrho¨nite by the substitution 2Be + 2Si > 4Al ranges from 3 to 7 cations and Si < 4 cations per (Figs 9, 11). XMg = 0.018À0.19 for høgtuvaite and 28 cations, implying considerable Al > Fe3+ makarochkinite, which are significantly less substitution at tetrahedral sites as inferred by magnesian than most rho¨nite. Phases intermediate Cosca et al. (1988). in Be content between høgtuvaite-makarochkinite After deducting the amount equivalent to Na + and rho¨nite-dorrite have not been reported. K, Si increases with total Ti from 3 atoms per Elements reported in amounts exceeding 500 28 cations in Ti-poor dorrite to an average of ppm in høgtuvaite and makarochkinite include about 6.3 atoms (range is 5.5À7.8) at Ti = 2 atoms Zn, Y, Sn, Nb, Ta and Th (Grauch et al., 1994; (ideal rho¨nite) and then decreases to Grew et al., 2005). 4.1À5.1 atoms in the Allende rho¨nite (Fig. 9). Rho¨nite is the only sapphirine-group mineral Serendibite reported to include compositions with both Mg/ (Mg + Fe2+) > 0.5 and Mg/(Mg + Fe2+) < 0.5. Ten The principal compositional variations in serendi- out of 122 rho¨nite compositions (excluding bite include the homovalent Fe > Mg, Fe > Al material in the Allende meteorite) accepted for substitutions, and the heterovalent (Mg,Fe) + Si > plotting in Fig. 9 gave, after stoichiometric 2(Al,Fe) (Tschermaks) and Na + Si > Ca + Al calculations, an excess of Fe2+ over Mg, e.g. substitutions (Grew et al., 1991a;VanDerveeret Mg/(Mg + Fe2+) = 0.16À0.42 for five samples al., 1993; Grew, 1996; Aleksandrov and Troneva, from Saint-Leu, Reunion Island (Havette et al., 2006). In terms of mole proportions (Mg,Fe,Mn)O, 1982). Meteoritic (angrite) and lunar rho¨nite are (Al,Fe)2O3,andSiO2, Na-poor serendibite ranges 2+ 2+ alsoclearly Fe -dominant with Mg/(Mg + Fe )= from SiO2 = (Mg,Fe,Mn)O = 0.33 (1:1:1 composi- 0.17 and 0.03, respectively. The latter is the only tion) to SiO2 = 0.36 (4:3:4 composition, which was rho¨nite with a normal Ti content (~2 per selected as the end-member, Table 1) via the 28 cations) to give Ti3+ when its formula is Tschermaks substitution. Compositions of Na- calculated on a 28 cation/40 oxygen basis (Fig. 9). bearing serendibite (with Na/(Na+Ca) ratioup to Manganese contents greater than 0.4 wt.% 0.15) are similar, but shifted tohigher Si because of MnO have not been reported in rho¨nite, but up the substitution Na + Si > Ca + Al. Boron content to 1.2 wt.% MnO has been found in dorrite ranges 2.8À3.3 atoms per 28 cations in most (Nickenicher-Sattel, Eifel, Germany, Kunzmann, analyses (2.91À3.26 B in three crystal-structure 1989 and pers. comm., 2007). Other constituents refinements, Van Derveer et al., 1993), whence our reported in rho¨nite include Cr (up to3.27 wt.% selection of 3 B in the end-member formula. Van Cr2O3 or 0.69 Cr per 28 cations from basanite, Derveer et al. (1993) obtained ion microprobe B Tergesh Pipe, Siberia, Timina et al., 2006) and V contents in two samples of 3.6 and 4.2 B atoms per (up to3.32. wt.% V 2O3 or 0.69 V per 28 cations, 28 cations, which they attributed to analytical error. Allende meteorite, Mason and Taylor, 1982). Savel’yeva et al. (1995) reported a serendibite from Scandium (0.32À0.38 wt.% oxide) is also the Ozyorskiy massif near Lake Baikal, Russia that reported in rho¨nite from Allende (Simon et al., is poorer in Si than the 1:1:1 composition and 1999). In contrast to aenigmatite, wilkinsonite, having a total of 96.69 wt.%, suggesting a B2O3 høgtuvaite and makarochkinite, high field- content of 3À4 wt.%, equivalent to1.3 À1.7 B per strength elements such as Nb and Zr have been 28 cations or about half that in the end-member very rarely sought in rho¨nite although it is likely formula. Composition of the Ozyorskiy serendibite they might substitute for Ti. in terms of the mole proportions (Mg,Fe,Mn)O, Høgtuvaite and makarochkinite are related by (Al,Fe)2O3 and SiO2 is estimated tobe 1:1.6:1 2+ 3+ the substitution Ti + Fe > 2Fe and form a (SiO2 = 0.27), i.e. midway between 4:3:4 solid solution series ranging from 0.5 to 1.3 Ti per serendibite (SiO2 = 0.36) and ideal dorrite (1:3:1 28 cations (Fig. 9). Mo¨ssbauer spectroscopy composition, SiO2 = 0.2). This could indicate suggests that Fe3+ preferentially occupies the M1, possible miscibility between dorrite and serendibite M2andM7sites,andFe2+,theM3ÀM6sites;only but for the large difference between the two afewpercentFe3+ was found at tetrahedral sites in minerals in Fe3+ and Al contents calculated to the crystal structure refinements (Grew et al., occupy octahedral sites. 2005). Both minerals contain 9 Si (generally 8.5 Si Possible Fe analogues constitute up to 26% of after deduction for alkalis) and 1 Al per 28 cations, natural serendibite, whereas MnO, TiO2 and other
859 E. S. GREW ET AL.
potential constituents do not exceed 0.5 wt.% disordered at M7, M3A and M4A, which are fully oxide. Total Fe as FeO ranges from 0.76 to occupied by Sb in type 1 welshite (Sb = 3). 14.75 wt.%, the extremes being reported by Schmetzer et al. (2002) and Nicollet (1990), Surinamite respectively. The most Fe-rich serendibite has Fe > Mg, but XFe2+ could not be calculated from Surinamite compositions closely approach the stoichiometry because there is no information on ideal formula (Table 1) with 12À25% of Fe2+ 3+ boron content. The maximum XFe2+ =0.26 substitution for Mg and 0À13% of Fe substitu- reported to date was calculated for a sample tion of viAl (Baba et al., 2000; Grew et al., 2000; containing 13.34 wt.% Fe as FeO from the Barbier et al., 2002). Proportions of Fe2+ and Fe3+ Tayozhnoye deposit, Siberia (Grew et al., were calculated from stoichiometry using ideal or 1991a). The proportion of Fe3+ equals or measured Be content, but in one case, Fe2+/Fe3+ exceeds Fe2+ content in most Fe-rich samples ratiowas determined by crystal structure refine- from this deposit and from the type locality (Grew ment and Mo¨ssbauer spectroscopy. MnO contents et al., 1991a, Van Derveer et al., 1993). The latter do not exceed 2 wt.%, whereas other constituents authors reported no evidence for tetrahedrally are present in amounts not exceeding a few 3+ coordinated Fe in Tayozhnoye serendibite, and tenths wt.%, e.g. 40.33 wt.% P2O5 (Grew, thus Fe3+/(Fe3+ + Al) ratioat octahedralsites can 2002). Ion microprobe analyses of surinamite be calculated from bulk Fe3+; it reaches 0.20 in from South Harris, Scotland gave a deficiency of these serendibite samples. 0.18À0.23 Be per 11 cations relative to the ideal formula with the charge balanced by a corre- sponding addition of divalent cations at the Welshite octahedral sites (Baba et al., 2000), i.e. by solid Most welshite samples studied by Grew et al. solution of 18À23% of a Be-free analogue of (2007), which included the type specimen (Moore surinamite, Mg4Al2O[Si3Al2O15], which Christy 1978) and one of the two samples analysed by and Putnis (1988) suggested could also be present Grew et al. (2001), had compositions intermediate as one-cell wide lamellae associated with stacking between the end-member given in Table 1, faults in sapphirine from Finero, Italy. 5+ 3+ Ca4(Mg9Sb3 )O4[Si6Be3AlFe2 O36], and an Fe- 5+ free equivalent, Ca4(Mg9Sb3 )O4[Si6Be3Al3O36], with the first being closer to the average. The 12 Recommended nomenclature tetrahedral sites in these samples (type 1) can be Introduction split intotwoequal subsets: (1) Si + As = 6 with up Todate, recognizingdistinct mineral species in to0.6 As, and (2) Al + Fe + Be = 6 with Be ranging the sapphirine supergroup has been ad hoc. This from 2.76 to 3.46 atoms per 28 cations and Al, approach was tolerated because most members from 0.99 to 2.47 atoms. Mn and Fe3+ are are distinct from one another in more than one subordinate substituents at octahedral sites. compositional variable, and their recognition as However, two samples (type 2, including the distinct species did not raise a problem. However, second of the two samples analysed by Grew et other members, notably rho¨nite-dorrite- al., 2001) showed much greater variation related høgtuvaite-makarochkinite solid solutions in by the coupled substitution MSb5+ + viMg2+ + which Mg, Fe and Ti are the dominant cations ivFe3+ > MFe3+ + viFe3+ + ivSi4+,whereM refers at octahedral sites, raised nomenclature problems. specifically tothe M7, M3A and M4A octahedral There is a large number of sites with extensive sites. This substitution relates the end-member cation disorder, and there are ambiguities in 5+ given in Table 1, Ca4(Mg9Sb3 )O4[Si6Be3Al determining the valence of Fe and Ti from 3+ Fe2 O36], with a hypothetical Sb-free end- electron microprobe analyses. The crystal struc- 3+ member, Ca4(Mg6Fe6 )O4[Si9Be3O36]ifAland tures of relatively few samples have been refined Fe3+ are considered together. The lowest measured (Table 2), and even crystal-structure refinements Sb reported by Grew et al. (2007) is 1.45 atoms provide only broad constraints on Fe and Ti per 28 cations in one compositional zone of a valence. For example, the distinction between highly heterogeneous grain of type 2 welshite, makarochkinite and høgtuvaite could only be about midway between the two end-members. A established by single crystal refinement that partial single-crystal refinement of a fragment from demonstrated that Ti is ordered at the M7 site. this grain found 1.64 Sb that appears to be partially Ordering of Ti at M7 alsodistinguishes rho¨nite
860 SAPPHIRINE AND SURINAMITE NOMENCLATURE
from dorrite. However, Mg and Ti are disordered in all subgroups), then by occupancies of the most in rho¨nite from the Allende meteorite, and Ti is polymerized T sites, and lastly by Mg/(Mg+Fe2+) not the dominant cation at M7 (Bonaccorsi et al., ratioat the M1ÀM6 sites (M1ÀM4, M8ÀM9in 1990). Tetrahedral compositions also raise ques- sapphirine). Further splitting of the supergroup tions. For example, høgtuvaite was originally based on occupancies other than those specified approved as a species distinct from rho¨nite below is not recommended. because its Be content approached 1 atom per The only other polysome found in nature, 20 O, i.e. Be appeared tofill onetetrahedral site. , TABLE 5. Examples of compositions in the sapphirine group containing substantial amounts of a potential new species, but not enough to qualify as new Sapphirine subgroup B analogue of sapphirine Mg4(Mg3Al9)O4[Si3B2Al7O36] Grew et al. (1990, 1991b, 1992) up to 25% of the B analogue Aenigmatite subgroup Mg analogue of aenigmatite Na4(Mg10Ti2)O4[Si12O36] Price et al. (1985 and unpublished data) reported Mg/(Mg + Fe2+) up to0.48 861 E. S. GREW ET AL. TABLE 6. Compounds related to the sapphirine supergroup, either synthetic or not strictly natural. Sapphirine group: * Combustion products found in waste dumps of coal mines in the Chelyabinsk basin. These products are considered to be substances formed by human intervention, and thus are not minerals (Nickel and Grice, 1998). { Formula is written assuming Al is all tetrahedrally coordinated, but an undetermined amount might be octahedrally coordinated (Hamilton et al., 1989). 862 SAPPHIRINE AND SURINAMITE NOMENCLATURE sapphirine (Mg), aenigmatite (Na), and rho¨nite symmetry and the M7 site is split intotwosites. In (Ca); the corresponding sites in sapphirine-1A are the sample for which a refinement is available, M7 M5 and M6 (Tables 2 and 3). Na and Ca at these and M7A are fully occupied by Sb and Mg, twosites are largely disordered,sothat the two respectively, i.e. ordering of Sb and Mg is sites can be considered as a unit in distinguishing complete within the error of the refinement. The the aenigmatite and rho¨nite subgroups. Na content presence of welshite containing only 1.45 Sb per (cut off at 2 Na per 28 cations) is the most readily 28 cations (vs. 3 in the ideal formula) and applied measure. Calcium could also occupy the 3.44 Fe3+ at octahedral sites suggests the possibi- M5 and M6 sites, which has been reported in lity of a Fe3+-dominant analogue of welshite with synthetic compounds (Hamilton et al., 1989; Fe3+ >(Sb+Mg)atM7 and M7A, but this could Arakcheeva, 1995; Sugiyama et al., 2005). In not be demonstrated by single-crystal refinement solid solutions between serendibite and (Grew et al., 2007). In contrast, Ti is not ordered at sapphirine-1A, i.e. Ca- and B-bearing sapphirine M7inrho¨nite from the Allende meteorite. (Grew et al., 1992), Ca, Na and Mg presumably Bonaccorsi et al. (1990) refined the occupancy at occupy the M5 and M6 sites, but it is not known M7 in a crystal from Allende to be 44% Ti, 56% whether there is any ordering. The report of a Fe- Mg and gave a formula for the analysed crystal as M8,M9 M5,M6 2+ M1ÀM4,M7 Sn-Ga-Ge phase possibly isostructural with (Ca4) (Mg3.4Fe0.6) (Mg2.4Al 3+ 4+ sapphirine (Johan and Oudin, 1986) suggests the V0.6Ti1.6Ti2.4)O4[Si4Al8O36]. Thus, the Allende possibility of a Fe2+-dominant subgroup. No rho¨nite does not qualify either as rho¨nite (Ti4+- mineral approaches an Mn-dominant subgroup: dominant at M7) or dorrite (Fe3+-dominant at M7). the maximum reported is 0.2 Mn at M8 and M9in We suggest that Allende rho¨nite be considered a makarochkinite, i.e. 5% occupancy at each site distinct species with Mg dominant at M7. (Grew et al., 2005). Although viFe3+/(viFe3+ + viAl) ratioreaches 0.20 in a serendibite from the Tayozhnoye deposit Third level: M7 site (see above), Fe3+/(Fe3+ + Al) = 0.091 at M7 in this Occupancy at the M7 site is used todistinguish sample (5152, Van Derveer et al., 1993), i.e. this species within the aenigmatite subgroup and sample contains only 9% of the Fe3+ analogue of species or clusters of species within the rho¨nite serendibite. subgroup; Al is dominant in both species of the Gasparik et al. (1999) synthesized Mg-analo- sapphirine subgroup. In most cases, smaller, more gues of wilkinsonite with Si > 12 atoms per highly charged cations, principally Al (sapphirine, 28 cations at 13À14 GPa and 1450À1700ºC, i.e. serendibite), Ti4+ (aenigmatite, rho¨nite, makar- Si occupies octahedral sites. One refinement gave ochkinite), Cr3+ (krinovite), and Nb5+ are ordered 0.806 (Mg, Si) + 0.194 Fe3+ at M7 and a relatively at M7. Fe3+ is the dominant cation at M7in short 863 E. S. GREW ET AL. al., 1998). Only Al is reported at the two Q3 sites principle, if such a sapphirine were found in Si-free ferrite (Mumme, 2003). In the three naturally, it would be a species distinct from sapphirines for which crystal structures are khmaralite because it would lack the super- available (Moore, 1969; Higgins and Ribbe, structure characteristic of khmaralite. 1979; Merlino, 1980), Si is the dominant cation By analogy with Be, we group the sites for B, at these twosites (Tables 2 and 3), an occupancy although BÀOÀB bridges are tolerated in that Christy et al. (1992) attributed topreference serendibite, and B occupancy at T1 and T4 can for SiÀOÀAl bridges. Al would be the dominant simultaneously exceed 50% by a significant cation at these two T sites in sapphirine containing amount, reaching 65% and 98%, respectively, in less than 2 Si per 28 cations (Fig. 6), i.e. less Si serendibite (Van Derveer et al., 1993). The than the composition Mg6Al10O4[Si2Al10O36]. possibility of a B-dominant analogue of Such sapphirine would be a distinct species, the sapphirine is suggested by the average composi- Al-dominant analogue. Sabau et al. (2002) tion reported by Grew et al. (1992) from reported a sapphirine with 1.709 Si per Johnsburg, New York. The B content of the 28 cations, which is the only composition we average (0.84 B per 28 cations) corresponds to found that would qualify as an Al-dominant 10% serendibite and 25% of a B-analogue of analogue of sapphirine. According to Christy et sapphirine, Mg4(Mg3Al9)O4[Si3B2Al7O36] al. (1992), sapphirine compositions with Si < 2 (Table 1). Although 25% is not sufficient to appear tobe unstable relative tospinel-bearing define a new species, study of the Johnsburg assemblages, and thus this species is expected to sample at higher resolution than was possible by be rare. Grew et al. (1992) might reveal patches In høgtuvaite, makarochkinite, serendibite and containing more of the Mg4(Mg3Al9)O4 khmaralite, Be and B are markedly ordered at [Si3B2Al7O36] end-member than of either of the both sites relative to the other T sites. Linkage serendibite or B-free sapphirine end-members, between T1 and T4 (rho¨nite subgroup) precludes and thereby qualify as a new B-dominant the presence of significantly more than 50% Be at analogue of sapphirine distinct from serendibite. both sites simultaneously in relatively disordered TEM study indicates that the sapphirine grains are structures, e.g. respectively, 44À48% and uniformly sapphirine-1A despite their chemical 46À52% in makarochkinite and, respectively, heterogeneity (Grew et al., 1992). 50% and 51% in høgtuvaite as BeÀOÀBe Ge and Ga are potential substituents at the bridges would result in underbonding of the T2(T4) and T3(T1) sites. There is a Fe-Sn-Ga-Ge bridging O (Christy et al., 2002; Grew et al., mineral possibly isostructural with sapphirine 2005). If the two sites are considered together, the (Johan and Oudin, 1986) and several synthetic Be content in end-member formulae is 2 per 28 compounds (Table 6), i.e. a Mg- and Ge-analogue cations, equivalent to filling one tetrahedral site. of wilkinsonite (Barbier, 1995) and Ga- and Ge In more ordered structures, occupancy reaches analogues of sapphirine-1A with 100% Be (welshite) and 70% Be (khmaralite), so MgO:Ga2O3:GeO2 ratios ranging from 3:5:1 the 50% rule could be applied to one site. almost to 3:1:2 (Barbier, 1990; 1998). A Na- Nonetheless, we would prefer to have a criterion Mn2+-Mn3+ germanate isostructural with aenig- based on bulk chemistry that would be applicable matite has been synthesized without any Ga toall sapphirine-groupminerals. Khmaralite was (Redhammer et al., 2008). distinguished from sapphirine by both the presence of a superstructure (doubled chain Fifth level: Mg/(Mg + Fe2+)ratio 2+ periodicity) and Be ordering (Barbier et al. A final criterion is Mg/(Mg + Fe )=XMg ratio 1999), but in the present nomenclature, the critical at M1ÀM6 sites (M1ÀM4, M8ÀM9in distinction is Be > 1 atom per 28 cations in sapphirine). With rare exception, each mineral khmaralite, which is roughly coincident with listed in Table 1 has been found to be either Mg- 2+ appearance of the superstructure (Grew et al., dominant, i.e. XMg > 0.5, or Fe -dominant, i.e. 2000). Christy et al. (2002) described a synthetic XMg < 0.5, at these M sites. However, XMg ranges beryllian sapphirine containing up to 2 Be per 28 from 1.00 to 0.03 in material described as rho¨nite. cations, e.g. Mg4(Mg4Al8)O4[Al4Be2Si6O36], but In this case, the 10 analyses giving XMg < 0.5 lacking the superstructure characteristic of khmar- correspond to the Fe2+-dominant analogue, which alite. The synthetic sapphirine is dominantly the is a distinct species (Table 4). The most 1A polytype with lamellae of the 2M polytype. In magnesian wilkinsonite (XMg = 0.53) is poten- 864 SAPPHIRINE AND SURINAMITE NOMENCLATURE tially a distinct species, and the most magnesian suggested that lamellae associated with stacking aenigmatite reported to date, XMg =0.48 faults in sapphirine from Finero, Italy could be a (Table 5), suggests the possibility of finding the Be-free analogue of surinamite. By analogy with Mg-dominant analogue of aenigmatite, which the sapphirine group, the criterion for distin- would also be a distinct species. guishing the Be-free analogue would be occu- According to Hatert and Burke (2008), this pancy of Al or Si instead of Be at the T1 site. criterion could be expanded to include other Barbier (1996, 1998) synthesized Ge- and Ga- divalent cations at the M1ÀM6 sites (M1ÀM4, analogues of Be-free surinamite in one of which M8ÀM9 in sapphirine) resulting in ternary and Ga and Ge occupy the T1 site (Table 6). higher order solid solutions, e.g. Mn, which is a significant, albeit subordinate, constituent at these sites in welshite, but is minor in other sapphirine- Possible new names and species group minerals. The new nomenclature does not result in new names for existing species. Names in current Other criteria usage (Tables 1, 4) remain unchanged. However, Further breakdown is possible because larger new names would be required for the composi- octahedral cations tend to be ordered at the M5 tions that we suggest are sufficiently distinct to be and M6 sites and larger tetrahedral cations at the recognized as new species in the above section T5andT6 sites. However, in many cases outlining our nomenclature. It would be prema- occupancies at these sites are correlated with ture for us to propose specific names here, but occupancies at the sites used to distinguish the only to summarize the compositional features different species, e.g. Fe ordering at M sites is indicating that the minerals in question are correlated with presence of Be in khmaralite distinct from recognized species. (Barbier et al., 1999). Grew et al. (2007) suggested the possibility of splitting out species Unnamed Al-analogue of sapphirine in welshite based on the dominance of Fe3+ and Al at T5andT6A. However, in one sample, Sabau et al. (2002) reported a peraluminous tetrahedral Fe3+ content is correlated with Sb sapphirine from the South Carpathians, content. Tetrahedral Fe3+ content in dorrite from Romania, for which the calculated formula the type locality is calculated to range from 0.4 to contained only 1.71 Si per 28 cations, i.e. less 5.5 atoms per 28 cations (Cosca et al., 1988), Si than the composition Mg6Al10O4[Si2Al10O36] suggesting the possibility of Fe3+ dominance at T5 (Fig. 6). In such a sapphirine, Al would be the and T6 in some samples but Al dominance in dominant cation at the T2 and T3 sites, i.e. the Al- others, i.e. two species could be split out on the dominant analogue of sapphirine. basis of T5 and T6 occupancy. However, further splitting would result in a needless proliferation of Unnamed Mg-analogue of wilkinsonite species, and is not consistent with earlier decisions by the CNMNC on sapphirine-group minerals. Recalculation of the analysis of wilkinsonite in a A special case is OH. Minerals of the syenitic ejectum from the inner caldera of the sapphirine group are presumed to be anhydrous, Wonchi volcano, Ethiopia (Gaeta and Mottana, 2+ and crystal structure refinements show no 1991) gave XMg (as Mg/(Mg + Fe Mn + Ni) = evidence for the presence of OH in natural 0.47, XFe2+ = 0.42, XMn = 0.10 and XNi = 0.01, i.e. material. However, an OH-bearing, Ti-free Mg Mg is the dominant divalent cation presumed to analogue of aenigmatite has been synthesized at occupy the M1ÀM6 sites. In principle the mineral 10 GPa and 1250ºC (Yang and Konzett, 2000), would be a new species because of the rule of the suggesting the possibility of OH incorporation at dominant constituent for homovalent ternary solid high pressure. solutions (Hatert and Burke, 2008). However, given the relatively small excess of Mg over Fe2+ and the large error in calculating Fe3+/Fe2+ ratio First level: 865 E. S. GREW ET AL. divalent cations than in other wilkinsonite, but also Allende mineral is the identity of the most significant Fe3+ is substituting for Si at tetrahedral abundant octahedrally coordinated trivalent sites (the composition cannot be plotted in Fig. 7), cation: Ti3+ vs.Fe3+ in rho¨nite and its Fe2+ whence the different formula given for a possible analogue (except one), whence the rationale for Mg analogue in Table 1. calling the Allende mineral an unnamed Ti3+- bearing Mg-analogue of rho¨nite. Unnamed Fe2+-analogue of rh˛nite Unnamed Fe-Sn-Ga-Ge mineral Recalculation of analyses of rho¨nite from (1) phonolitic differentiate, Puy de Saint- Johan and Oudin (1986) reported a Fe-Sn-Ga-Ge Sandoux, Auvergne, France (Gru¨nhagen and mineral in grains about 15 mm across in sphalerite Seck, 1972), (2) coral penetrated by basalt at from Montauban, Haute Garonne, France. The Saint-Leu, Reunion Island (Havette et al., 1982), grains have pseudohexagonal outlines. In calcu- (3) basanite, Scania, Sweden (Olsson, 1983) and lating formulae from electron microprobe (4) a spinel-wehrlite xenolith from Foster Crater, analyses, Johan and Oudin (1986) reported that McMurdo Volcanic Group, Antarctica (Gamble assuming 7 cations and 10 oxygens gave a better and Kyle, 1987) gave Mg/(Mg + Fe2+)= stoichiometry (e.g. Table 7) than assuming 0.156À0.499. In addition, Mg/(Mg + Fe2+)= 3 cations and 4 oxygens (spinel stoichiometry); 0.17 and 0.03 in rho¨nite from angrite Northwest our attempt to calculate a formula assuming Africa 4590 (Kuehner and Irving, 2007) and the 3 cations and 4 oxygens from the six published Luna 24 regolith (Treiman, 2008), respectively, analyses gave negative Fe3+ contents (from 10 to and identity of the analysed grain in Luna 24 as 12 wt.% Fe2O3). It is thus unlikely the mineral is rho¨nite was confirmed by Raman spectroscopy. a spinel, and we concur with the conclusion Even allowing for the large uncertainty in the calculation based on stoichiometry, we conclude that most of these rho¨nite samples are clearly TABLE 7. Selected compositions of unnamed Fe-Sn- Fe2+-dominant and distinct from other rho¨nite, i.e. Ga-Ge mineral (from Johan and Oudin, 1986) they are the Fe2+-dominant analogue. Many of the compositions are also distinct in other ways, e.g. the Reunion Island rho¨nite contains more Ti than Analysis 3 6 most (2.43À3.00 Ti per 28 cations, Fig. 9). Wt.% Trivalent cations at the M sites in this and the GeO2 8.68 5.07 angrite rho¨nite are calculated tototal0 À1.5 per SnO2 14.63 13.12 28 cations, less than in the end-member formula Fe2O3 5.97 4.34 for rho¨nite. Our proposed end-formula for the Ga2O3 45.94 55.33 unnamed Fe-analogue of rho¨nite (Table 1) MnO 0.74 0.85 approximates Treiman’s (2008) formula of the FeO 19.79 15.90 lunar rho¨nite, although its composition differs in ZnO 3.93 4.46 its high Si and low Al contents from other rho¨nite Sum 99.68 99.07 (Figs 9, 11) Formulae Ge 2.153 1.270 iv Unnamed T|3+-bearing Mg-analogue of rh˛nite Ga 9.847 10.730 Sum T 12.000 12.000 Rho¨nite that is associated with melilite, ‘fassaite’, spinel and perovskite in inclusions in the Allende Sn 2.518 2.281 vi meteorite contains 3.20 to 4.57 Ti per 28 cations Ga 2.869 4.741 3+ (Fuchs, 1971, 1978; Maoand Bell, 1974; Mason Fe 1.941 1.426 and Taylor, 1982; Simon et al., 1999) and the Zn 1.253 1.436 Mn 0.271 0.314 calculated proportion of Ti3+ increases with total Fe2+ 7.148 5.801 Ti (Fig. 9). Ti is not ordered at M7; instead, Mg is dominant at this site (Bonaccorsi et al., 1990), an Sum M 16.000 15.999 M7 occupancy that distinguishes the Allende mineral from both rho¨nite (Ti4+-dominant) and Electron microprobe analyses. Formula and Fe3+/Fe2+ dorrite (Fe3+-dominant). A salient feature of the ratio calculated assuming 28 cations and 40 oxygens. 866 SAPPHIRINE AND SURINAMITE NOMENCLATURE reached by Johan and Oudin (1986) that the Geochemistry International, 44(7), 665À680). mineral could be related to sapphirine. Alletti, M., Pompilio, M. and Rotolo, S.G. (2005) Mafic Nonetheless, XRD data will be needed to and ultramafic enclaves in Ustica Island lavas: confirm the relationship. The analysed grains Inferences on composition of lower crust and deep range in Ga2O3 content from 45.9 to 55.3 wt.% magmatic processes. Lithos, 84, 151À167. (e.g. Table 7) and the most important substitution Arakcheeva, A.V. (1995) Crystal structure of the appears tobe ivGe + viFe2+ > ivGa + viGa, but baykovite mineral. Crystallography Reports, 40, substitutions such as viSn + viFe2+ > 2viGa and 220À227. Fe3+ > Ga (at either M or T sites) probably also Arakcheeva, A.V. and Ivanov, I.T. (1993) Crystal structure of disomatic phase of variable composition play a role. I II I CaAl(Al,V,M )2(V,M )(Si,Al)2O10, where M = Mg, MII = Al, Fe, Mn, Ti, Mg: its polytypic modifications Unnamed Be-free analogue of surinamite and structural homologs. Kristallografiya, 38, 144À161 (in Russian). Christy and Putnis (1988) reported one-cell wide Arakcheeva, A.V., Karpinskii, O.G. Lyadova, V.Ya. layers having the surinamite structure in TEM (1991) Crystal structure of a CaFe3AlO7 alumi- images of sapphirine from Finero, Italy, in which numÀcalcium ferrite of variable composition. Soviet the 1A,2M and 4M polytypes are present. The Physics, Crystallography, 36, 332À336. surinamite-like lamellae are attributed to b/5 A˚ sheim, A., Berge, S.A., and Larsen, A.O. (2008) stacking faults on (010), along which every Sporelementer i ænigmatitt fra Larvik plutonkom- fourth spinel-like layer is missing, i.e. pleks. Norsk Bergverksmuseum, Skrift, 38,63À65 (in 867 E. S. GREW ET AL. Khmaralite, a new beryllium-bearing mineral related Mineralogist, 92, 735À747. tosapphirine: A superstructure resulting frompartial Bro¨gger, W.C. (1887) Forelo¨big meddelelse om ordering of Be, Al and Si on tetrahedral sites. mineralerne pa˚ de sydnorske augit- og nefelinsye- American Mineralogist, 84, 1650À1660. niters grovkornige gange. Geologiska Fo¨reningens i Barbier, J., Grew, E.S., Ha˚lenius, E., Ha˚lenius, U. and Stockholm Fo¨rhandlingar, 9, 247À274 (in Danish). Yates, M.G. (2002) The role of Fe and cation order Bro¨gger, W.C. (1890) Mineralien der su¨dnorweg. in the crystal chemistry of surinamite, Augitsyenite. 50. 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