Mineralogical Magazine, August 2013, Vol. 77(6), pp. 2825–2839
The dumortierite supergroup. I. A new nomenclature for the dumortierite and holtite groups
1, 2 3 2 4 4 A. PIECZKA *, R. J. EVANS ,E.S.GREW ,L.A.GROAT ,C.MA AND G. R. ROSSMAN 1 Department of Mineralogy, Petrography and Geochemistry, AGH-University of Science and Technology, Mickiewicza 30, Krako´w, 30-059, Poland 2 Department of Earth, Ocean and Atmospheric Sciences, University of British Columbia, 6339 Stores Road, Vancouver, British Columbia, V6T IZ4, Canada 3 School of Earth and Climate Sciences, University of Maine, Bryand Global Science Center, Orono, Maine, 04469- 5790, USA 4 Division of Geological and Planetary Sciences, California Institute of Technology, MS 170-25, Pasadena, California, 91125-2500, USA [Received 26 December 2013; Accepted 11 July 2013; Associate Editor: A. Christy]
ABSTRACT
Although the distinction between magnesiodumortieite and dumortierite, i.e. Mg vs. Al dominance at the partially vacant octahedral Al1 site, had met current criteria of the IMA Commission on New Minerals, Nomenclature and Classification (CNMNC) for distinguishing mineral species, the distinction between holtite and dumortierite had not, since Al and Si are dominant over Ta and (Sb,As) at the Al1 and two Si sites, respectively, in both minerals. Recent studies have revealed extensive solid solution between Al, Ti, Ta and Nb at Al1 and between Si, As and Sb at the two Si sites or nearly coincident (As,Sb) sites in dumortierite and holtite, further blurring the distinction between the two minerals. This situation necessitated revision in the nomenclature of the dumortierite group. The newly constituted dumortierite supergroup, space group Pnma (no. 62), comprises two groups and six minerals, one of which is the first member of a potential third group, all isostructural with dumortierite. The supergroup, which has been approved by the CNMNC, is based on more specific end-member compositions for dumortierite and holtite, in which occupancy of the Al1 site is critical. (1) Dumortierite group, with Al1 = Al3+,Mg2+ and &,where& denotes cation vacancy. Charge balance is provided by OH substitution for O at the O2, O7 and O10 sites. In addition to dumortierite, endmember composition AlAl6BSi3O18, and magnesiodumortierite, endmember composition MgAl6BSi3O17(OH), plus three endmembers, ‘‘hydroxydumortierite’’, &Al6BSi3O15(OH)3 and two Mg-Ti analogues of dumortierite, (Mg0.5Ti0.5)Al6BSi3O18 and (Mg0.5Ti0.5)Mg2Al4BSi3O16(OH)2, none of which correspond to mineral species. Three more hypothetical endmembers are derived by homovalent substitutions of Fe3+ for Al and Fe2+ for Mg. (2) Holtite group, with Al1 = Ta5+,Nb5+,Ti4+ and &. In contrast to the dumortierite group, vacancies serve not only to balance the extra charge introduced by the incorporation of pentavalent and quadrivalent cations for trivalent cations at Al1, but also to reduce repulsion between the highly charged cations. This group includes holtite, endmember composition (Ta0.6&0.4)Al6BSi3O18, nioboholite (2012-68), endmember composition (Nb0.6&0.4)Al6BSi3O18, and titanoholtite (2012-69), endmember composition (Ti0.75&0.25)Al6BSi3O18. 3+ (3) Szklaryite (2012-70) with Al1 = & andanendmemberformula&Al6BAs3 O15. Vacancies at Al1 are caused by loss of O at O2 and O7, which coordinate the Al1 with the Si sites, due to
* E-mail: [email protected] DOI: 10.1180/minmag.2013.077.6.09
# 2013 The Mineralogical Society A. PIECZKA ET AL.
replacement of Si4+ by As3+ and Sb3+, and thus this mineral does not belong in either the dumortierite or the holtite group. Although szklaryite is distinguished by the mechanism introducing vacancies at the Al1 site, the primary criterion for identifying it is based on occupancy of the Si/As,Sb sites: (As3+ + Sb3+)>Si4+ consistent with the dominant-valency rule. A Sb3+ analogue to szklaryite is possible.
KEYWORDS: dumortierite group, holtite group, nioboholtite, titanoholtite, szklaryite, nomenclature, crystal chemistry.
Introduction Harold E. Holt, Prime Minister of Australia from 1966 to 1967, and its crystal structure refined by AS presently constituted, the dumortierite group Hoskins et al. (1989). It is known only from comprises three minerals: dumortierite, complex granitic pegmatites, having been (Al,&)Al6BSi3O16(O,OH)2, magnesiodumor- reported from three other localities: Voron’i tierite, (Mg,&)Al6BSi3O16(O,OH)2, and holtite, Tundry, Kola Peninsula, Russia (Voloshin et al., (Al,Ta,&)Al6B(Si,Sb,As)S3O15(O,OH,&)S3, 1977; 1987; Voloshin and Pakhomovskiy, 1988); where & denotes cation or anion vacancy. Szklary, Lower Silesia, Poland (Pieczka and Dumortierite is second only to tourmaline-super- Marszałek, 1996; Pieczka et al.,2011),and group minerals as the most abundant B-bearing Virorco, San Luis range, Argentina (Galliski et phase in metamorphosed pelitic and psammitic al., 2012). In contrast to the situation for many rocks, aluminous metasomatic rocks and granitic new minerals described in the last 50 years, none plutonic rocks (Grew, 2002). It was first reported of the four constituents that distinguish holtite in 1880 from pegmatitic veins near Lyon, France from dumortierite is dominant at a specific (Bertrand, 1880; Gonnard, 1881), and named for crystallographic site, e.g. Si is dominant over the French palaeontologist Euge`ne Dumortier. It Sb3+ and As3+ at the two tetrahedral sites and Al took many years for the full complexity of is dominant over Ta, Nb and vacancy at the Al1 dumortierite chemistry to be revealed, e.g. that it site in both minerals. Voloshin et al. (1977, 1987) contains essential B (Schaller, 1905), and that its introduced the terms ‘‘holtite I’’ and ‘‘holtite II’’ cation and OH contents are non-stoichiometric for clusters of holtite compositions differing in (Golovastikov, 1965; Moore and Araki, 1978). (As+Sb) content, but compositions from other Until about 1995, P2O5, MgO, TiO2,Fe2O3 and localities, particularly the Szklary pegmatite, FeO were thought to be the most abundant filled the apparent gap between the two composi- constituents other than H2O, B2O3,Al2O3 and tions (Pieczka et al., 2011). Groat et al. (2009) SiO2 (Grew, 2002), but more recent work has suggested the clustering could be an artifact shown that As2O3,Sb2O3,Ta2O5 and Nb2O5 are resulting from there being two generations of also present in substantial quantities, and a few holtite formed in different chemical environments samples contain Bi, presumably as Bi3+ (e.g. at Voron’i Tundry, rather than from a crystal- Groat et al., 2001, 2012; Cempı´rek and Nova´k, lographic control. Moreover, the compositional 2005; Borghi et al., 2004; Vaggelli et al., 2004; range in holtite from the Szklary pegmatite Cempı´rek et al., 2010; Pieczka et al., 2011). extended to higher (Sb+As) contents than the Magnesiodumortierite was reported as the Mg- high (Sb+As) composition of ‘‘holtite II’’ (Pieczka dominant analogue of dumortierite from ultra- et al., 2011). high-pressure rocks at Dora Maira in the Italian In the absence of a rigorous definition, the term Alps (Chopin et al., 1995; Ferraris et al., 1995). holtite was being applied indiscriminately to an The most magnesian compositions reported by ever-widening compositional range, while dumor- Visser and Senior (1991 and unpublished data) tierite was found to contain substantial amounts of and by Kihle (1989 and unpublished data) in the elements that supposedly distinguish holtite dumortierite from the Bamble Sector, Norway, from dumortierite. The end result is that might also qualify as magnesiodumortierite distinction between holtite and dumortierite has (Chopin et al., 1995; Grew, 2002), but to date become blurred, and consequently, we are no other occurrence has been reported. recommending a new classification of the Holtite was first described from alluvial dumortierite group in which the minerals are deposits formed from pegmatite at Greenbushes, distinguished on the basis of crystal chemistry and Western Australia (Pryce, 1971) and named for consistently with current CNMNC practice.
2826 DUMORTIERITE SUPERGROUP NOMENCLATURE
Crystal structure of dumortierite and related dered, which results in an average chain length minerals that can be adjusted to fit the repeat distance of the remaining octahedral framework in the The crystal structure of dumortierite (Fig. 1), structure (Moore and Araki, 1978). Evans et al. space group Pnma (no. 62), was described by (2012) reported that when there is minor Golovastikov (1965) and Moore and Araki (1978) substitution for Al at Al1, three distinct sub-sites as a design on the semi-regular planar net of Al1 could be distinguished depending on which {6·4·3·4}, which Moore and Araki (1978) adjacent Al1 sites were occupied; each sub-site showed can be broken down into four regions: was found to be ~ occupied. Such ordering (1) [AlO3] chains of face-sharing octahedra (the would not be expected in compositions with more Al1 sites) with circumjacent ‘‘pinwheels’’ of six substitution at Al1. Although Al cations in SiO4 tetrahedra, two Si1 and four Si2 sites; individual face-sharing Al1 octahedral chains (2) [Al4O12] cubic close-packed chains parallel to are ordered, cations from chain to chain are the [100] direction, containing the Al2 and Al3 disordered, preserving Pnma symmetry. octahedral sites, that are joined to equivalent Groat et al. (2012) reported splitting of the two chains by reflection at the O1 corners of the Al2 (As, Sb) sites into four distinct As1, Sb1, As2 and octahedra to form [Al4O11]sheetsoriented Sb2 positions, and the single Al1 site split into parallel to (001); (3) [Al4O12]double-chains three Al1a, Al1 and Al1b positions whose parallel to the [100] direction containing the Al4 occupancies refined to Al1 > Al1a > Al1b in octahedral sites with some face-sharing; and dumortierite containing a significant amount of (4) BO3 triangles. The Al1ÀAl1 distance is As and Sb, but relatively little Ta and Nb. The ~2.35 A˚ , which is unusually short for face- unequal occupancies suggest that the hexagonal sharing octahedra, and the Al1 site is on average tunnels contain a disordered mix of face-sharing 75% occupied by Al (e.g. Moore and Araki, octahedral dimers, trimers and longer units 1978). The Al1 face-sharing chains are disor- separated by vacancies. The splitting does not
FIG. 1. The crystal structure of dumortierite viewed down the a axis. Pnma setting (from Groat et al., 2009, 2012).
2827 A. PIECZKA ET AL.
result in a superstructure, which was reported in a tunnels bounded by the two regions composed dumortierite-like mineral found as fibres in rose of [Al4O12] chains (Fig. 1). Both SiO4 tetrahedra 3+ quartz (Applin and Hicks, 1987; Goreva et al., are replaced partially by Sb O3 triangular 2001; Ma et al., 2002). This mineral differs from pyramids (As3+ is dominant at this site in dumortierite in having a superstructure with the b szklaryite, Fig. 2) with no evidence of preference and c dimensions doubled (Pnma orientation), of Sb for one of the Si sites, and Ta replaces Al at which Ma et al. (2002) attributed to ordering of Ti the Al1 position. As a result, there are vacancies and Fe at ‘‘Type II’’ Al1 sites and Al at ‘‘Type I’’ at the coordinating anion sites (O2 and O7) as Al1 sites with ‘‘Type I’’ and ‘‘Type II’’ having a well as at the Al1 site. Relative to the Si positions, regular distribution in (100). Ma et al. (2002) the Sb3+ sites are shifted ~0.5 A˚ closer to the Al1 reported that (Fe + Ti) ranged from 0.28 to position to accommodate the longer Sb3+-anion 0.34 a.p.f.u. (18 O basis), which is above average, bonds (average ~1.9 A˚ ). When the Sb sites are but within the reported range for dumortierite occupied, O2 (for Si1) and O7 (for Si2) positions (Grew, 2002). Thus, the ordering could be related are vacant. Hoskins et al. (1989) obtained the to the relatively low temperatures of exsolution of formula (Si2.25Sb0.75)B[Al6(Al0.43Ta0.27&0.30) the fibres from quartz as Ma et al. (2002) O15(O,OH)2.25](Z = 4) from their crystal- suggested, and not to composition. structure study. Even for zero OH content, this In magnesiodumortierite, Mg substitutes for Al formula has an excess positive charge of +0.39. at the Al1 and Al4 sites, but Mg > Al only at Al1 Kazantsev et al. (2005, 2006) refined the crystal (Chopin et al., 1995; Ferraris et al., 1995). structure of an As-bearing ‘‘holtite I’’ crystal from Hydroxyl in dumortierite and magnesiodumor- Voron’i Tundry to R = 0.046. They reported that tierite is thought to occur at the O2 and O7 As3+ is incorporated into the crystal structure in positions (e.g. Moore and Araki, 1978; Alexander (Sb,As)O3 pyramids substituting for SiO4 tetra- et al., 1986; Cempı´rek and Nova´k, 2005; Fuchs et hedra just as SbO3 pyramids substitute for SiO4 al., 2005), and at the four-coordinate O10 site tetrahedra in holtite from Greenbushes, and there (Ferraris et al., 1995; Farges et al., 2004). was no preference for one of the two Si positions. Hoskins et al. (1989) showed that the crystal In their refinement of four holtite crystals, Groat structure of holtite is closely related to that of et al. (2009) reported that charge-balance dumortierite, but differs in several important calculations suggest that essentially no water is respects, all of which lie within six-sided present, but that Fourier transform infrared
FIG. 2. The six-sided tunnels (region 1 of Moore and Araki, 1978) filled with Al1 octahedra and SiO4 tetrahedra in dumortierite, (As,Sb)O3 groups in the new mineral szklaryite, or a mixture of (Sb,As)O3 groups and SiO4 tetrahedra in holtite (after Hoskins et al., 1989; Groat et al., 2009, 2012). Al1 is largely vacant in szklaryite.
2828 DUMORTIERITE SUPERGROUP NOMENCLATURE
spectra confirm that some OH is present at the O2 polymorph ‘‘would be far from straightforward,’’ and O7 positions. Their proposed general formula and thus including these three minerals in the for holtite is Al7À[5x+y+z]/3(Ta,Nb)x&[2x+y+z]/3B dumortierite supergroup is not warranted. Evans Si3Ày(Sb,As)yO18ÀyÀz(OH)z, where x is the total and Groat (2012) grouped the dumortierite number of pentavalent cations, y is the total supergroup, ellenbergerite, phosphoellenbergerite, amount of Sb + As and z 4 y is the total amount ekatite and a host of synthetic compounds of OH. The splitting of (Sb, As) and Al1 sites together as ‘‘dumortierite-like materials.’’ observed in dumortierite has not been found in We agree with Ferraris et al. (1995) and Keller holtite (Groat et al., 2012). (2001) that the differences are significant enough In crystallographic studies of dumortierite, that ellenbergerite, phosphoellenbergerite and magnesiodumortierite and holtite, B has been ekatite should remain separate from the dumor- reported to occupy only the trigonal site, which is tierite supergroup. Ferraris et al. (1995) empha- confirmed by study of B K-edge spectra (Garvie et sized that the difference in the two structures al., 1995; Fleet and Muthupari, 2000). No involves more than simply replacing Al2ÀAl3 evidence for deviation from stoichiometry been chains in dumortierite with copies of the Al4 reported for B in the crystal structure refinements, chains. The tetrahedral groups in each hexagonal which is consistent with B contents reported in channel give the channel a defined orientation. synthetic dumortierite by Werding and Schreyer Ferraris et al. (1995) described how both the (1990; cf. Ono 1981). Chemical determination of dumortierite and ellenbergerite structures can be B content is difficult both by wet methods, decomposed into slabs parallel to the [Al4O11] because dumortierite supergroup minerals are sheets. In the hexagonal structure, hexagonal often finely fibrous and impure, and by electron channels have the same orientation in every or ion microprobe because of problems with slab, whereas in the orthorhombic structure, the matrix correction and standardization. Thus, it is hexagonal channels reverse orientations every not surprising that a wide range of B contents has other slab. The Al2ÀAl3-type chains show been reported, e.g. the non-stoichiometric B similar alternating orientations. Ferraris et al. content obtained by wet chemical analysis in (1995) argued that this made an orthorhombic-to- type holtite, 1.82 wt.% B2O3 (Pryce, 1971), which hexagonal transition in dumortierite unlikely, as was later shown to be in error by single-crystal such a transition would involve inverting half the refinement (Hoskins et al., 1989). In other cases, structure. There is also a significant difference in B contents less deviant from stoichiometry, or the triangular channels. The triangular channel in even approaching it, were reported using wet all the dumortierite supergroup minerals contains chemical (e.g. Claringbull and Hey, 1952; only trigonal-planar borate groups, whereas the Voloshin et al., 1977; Chopin et al., 1995), ion minerals related to ellenbergerite each contain microprobe (Willner and Schreyer, 1991), and multiple tetrahedral or pyramidal groups: silicate electron microprobe analyses (Vra´na, 1979; and phosphate in ellenbergerite (Chopin et al., Chopin et al., 1995; Fuchs et al., 2005; Pieczka 1986); phosphate and (trigonal planar) carbonate et al., 2013), but the precision was too low to in phosphoellenbergerite (Raade et al., 1998); and properly assess whether the observed deviations silicate and arsenite in ekatite (Keller, 2001). The are significant. lack of any known substitution at the B site in dumortierite minerals is very distinctive and might be related to the other differences Relationship to ellenbergerite, between the dumortierite and ellenbergerite phosphoellenbergerite and ekatite structures, the latter of which appears to Dumortierite supergroup minerals have a strong incorporate negligible B: Ferraris et al. (1995) structural affinity with the isotypic hexagonal considered it significant that ellenbergerite found species ellenbergerite, phosphoellenbergerite and in contact with magnesiodumortierite contains ekatite. Moore and Araki (1978) implied that only 10 ppm B. transformation of the orthorhombic dumortierite into a hexagonal dimorph might be relatively Nomenclature of the dumortierite simple in principle. However, as pointed out by supergroup Ferraris et al. (1995) (and later by Keller, 2001, and Evans and Groat, 2012), transformation of The new classification for the dumortierite group dumortierite into an ellenbergerite-type hexagonal has been approved by the IMA Commission on
2829 TABLE 1. A classification of the dumortierite supergroup.
Mineral Endmember formula Relationship with dumortierite
———————————— Dumortierite group ———————————— Dumortierite AlAl6BSi3O18 3+ 3+ Al1 3+ Al1 Fe analogue of dumortierite Fe Al6BSi3O18 Fe ? Al Al1 Al1 Al1 Mg-Ti analogue of dumortierite (Mg0.5 Ti0.5 )Al6BSi3O18 Mg + Ti ? 2 Al 2+ 2+ Al1 2+ Al1 Al1 Fe -Ti analogue of dumortierite (Fe0.5 Ti0.5 )Al6BSi3O18 Fe + Ti ? 2 Al
# Al1 Al1 Al1 Al4 Al4 PIECZKA A. ‘‘Titano-magnesiodumortierite’’ (Mg0.5 Ti0.5 )Mg2Al4BSi3O13(OH)2 Mg + Ti ? 2 Al; Mg + OH ? Al Al1 Al1 Magnesiodumortierite MgAl6BSi3O17 (OH) Mg + OH ? Al + O 2+ 2+ Al1 2+ Al1
2830 Fe analogue of magnesiodumortierite Fe Al6BSi3O17(OH) Fe +OH? Al + O Al1 Al1 ‘‘Hydroxydumortierite’’ &Al6BSi3O15 (OH)3 & + 3OH ? Al + 3O
———————————— Holtite group ———————————— AL. ET Al1 Al1 Al1 Holtite (Ta0.6 &0.4 )Al6BSi3O18 0.6 Ta + 0.4 &? Al Al1 Al1 Al1 Nioboholtite (Nb0.6 &0.4 )Al6BSi3O18 0.6 Nb + 0.4 &? Al Al1 Al1 Al1 Titanoholtite (Ti0.75 &0.25 )Al6BSi3O18 0.75 Ti + 0.25 &? Al —————————— Potential group —————————— 3+ Al1 3+ Al1 4+ Szklaryite &Al6BAs3 O15 & + 3As ? Al + 3Si 3+ Al1 3+ Al1 4+ Sb analogue of szklaryite &Al6BSb3 O15 & + 3Sb ? Al + 3Si
Bold À Mineral approved by the IMA Commission. #A major constituent of magnesiodumortierite. DUMORTIERITE SUPERGROUP NOMENCLATURE
New Minerals, Nomenclature and Classification (2) Holtite group: Vacancies serve not only to (CNMNC proposal 12-C, November 6, 2012). balance the extra charge introduced by the The group is now considered a supergroup as it incorporation of pentavalent and quadrivalent can be subdivided into three groups (one is cations for trivalent cations at Al1, but also to potential as only one representative has been reduce repulsion between the highly charged found to date) on the basis of the differences in cations. the substitution mechanisms that decrease occu- (3) Potential group including szklaryite. pancy at the Al1 site, which is the basis of the Vacancies at Al1 are caused by loss of O2 and classification (Table 1, Fig. 3). It is important to O7, which coordinate the Al1 with the Si sites, note that up to 5% vacancies have been reported due to replacement of Si4+ by As3+ and Sb3+, and at the other three octahedral Al sites, which are thus this mineral does not belong in either the generally believed to be real (e.g. Fuchs et al., dumortierite or the holtite group. An Sb3+ 2005; Groat et al., 2012), although Moore and analogue to szklaryite is possible. Araki (1978) and Alexander et al. (1986) inferred that vacancies at these sites resulted from Dumortierite group correlation between the site occupancies and atomic displacement parameters. In addition, Mg The dumortierite group includes eight endmem- substitution for Al at Al4 is reported for bers (Table 1), two of which are major constitu- magnesiodumortierite, Al4Mg + OH ? Al4Al + ents of naturally occurring minerals: dumortierite, O (Chopin et al., 1995; Ferraris et al., 1995). endmember composition AlAl6BSi3O18,and However, for the purposes of the classification we magnesiodumortierite, endmember composition only consider the Al1 site because Al is over- MgAl6BSi3O17(OH) (Fig. 4). In general, classifi- whelmingly dominant at the other Al sites, cation of the dumortierite group follows the excepting the ~50% Al at Al4 in Ti-rich dominant-valency rule (Hatert and Burke, 2008) magnesiodumortierite (Chopin et al., 1995; as the formulae given for three corners of the Ferraris et al., 1995). tetrahedron represent different valences at the Al1 We have identified three distinct mechanisms site, i.e. 0 (&), 2 (Mg, Fe2+) and 3 (Al, Fe3+), 2+ for introducing vacancies at Al1, which gives us whereas the fourth corner (Mg,Fe )0.5Ti0.5 can be two groups and a potential group: considered a case of valency-imposed double site- (1) Dumortierite group: Charge-balance for occupancy. vacancies at Al1 is provided by OH substitution The Al1 site has not been reported to be fully for O at the O2, O7 and O10 sites. occupied by Al, the maximum occupancy being
FIG. 3. Subdivision of the dumortierite supergroup into two groups and one potential group on the basis of Al1 occupancy. Fe3+ is added to Al and Fe2+ to Mg. Ti is considered a constituent of dumortierite only if coupled with Mg and Fe2+.
2831 A. PIECZKA ET AL.
= 0.6 per 18 O and Fe assumed to be Fe3+ and added to dumortierite (dominant-valency rule), the magnesiodumortierite endmember is no longer dominant. Several other dumortierite samples from the Bamble Sector contain >3 wt.% MgO (Visser and Senior, 1991 and unpublished data; Kihle, 1989 and unpublished data), and formulae give nearly equal proportions of the magnesiodumortierite and dumortierite endmembers. As compositions straddle the boundary between the two minerals, determining whether any dumortierite from the Bamble Sector is magnesiodumortierite would require precise measurements of water content and iron valence. Iron contents of dumortierite-group minerals range from 0 to 5.94 wt.% Fe as Fe2O3 FIG. 4. By combining Fe with Al and Mg, the (Claringbull and Hey, 1958; Grew, 2002; Groat dumortierite group can be represented by a four- and Evans, unpublished data), but determining its component system (inset) with most compositional valence requires wet chemistry (titrations) or a variation in the Ti-free system (triangle), where two spectroscopic method. Platonov et al. (2000) recognized minerals and one hypothetical component attributed the marked blue, violet and red are recognized on the basis of Al1 occupancy. coloration and pleochroism to Fe2+-Ti4+ inter- valence charge transfer with little, if any contribution from Fe2+-Fe3+ charge transfer, 88% (Alexander et al., 1986, not including their whereas Goreva and Rossman (2000) found 0.95 empirical correction; Groat et al., 2012), and evidence that pink and blue colours were due to it appears that the dumortierite endmember Fe2+-Ti4+ intervalence charge transfer and 2+ 3+ AlAl6BSi3O18 is unattainable due to face-sharing Fe -Fe intervalence charge transfer, respec- in the chain of Al1 octahedra. Instead, all tively, in nano-inclusions of a dumortierite-like naturally occurring dumortierite is a mixture of phase in quartz, consistent with the findings that this composition with others, most commonly, the Fe3+ is also involved in coloring dumortierite ‘‘hydroxydumortierite’’ component, (Alexander et al., 1986; Farges et al., 2004; Fuchs &Al6BSi3O15(OH)3 (Moore and Araki, 1978), et al., 2004). Mo¨ssbauer spectroscopy also shows which Werding and Schreyer (1990) cited as that both Fe2+ and Fe3+ are present in dumortierite constituting up to 33% of dumortierite synthe- (Farges et al., 2004). Thus, three endmembers 3+ sized at pressures from 3 to 20 kbar in the Al2O3– involving homovalent substitutions of Fe and 2+ Al1 Al1 SiO2–B2O3–H2O system. Natural dumortierite Fe for Al and Mg, respectively, are with relatively few impurities is estimated to theoretically possible (Table 1), although the Fe contain <30% &Al6BSi3O15(OH)3 (Moore and contents of natural material are never sufficient Araki, 1978; Alexander et al., 1986; Cempı´rek for an Fe analogue to be dominant. and Nova´k, 2005; Fuchs et al., 2005). The TiO2 contents range from 0 to >4 wt.%, i.e. Except for magnesiodumortierite from the type reaching 4.3 and 4.6 wt.% in dumortierite from an locality, Dora Maira, the maximum MgO content unspecified locality in Mozambique and of 3.42 wt.% was reported by Visser and Senior Rogaland, Norway, respectively (Borghi et al., (1991) in a dumortierite from the Bamble Sector, 2004; Huijsmans et al., 1982), but Visser Norway. Assuming OH = 0.75 per 18 O, the (unpublished data) obtained up to 5.10 and composition of this dumortierite gives an Al1 5.24 wt.% (corresponding to 0.37À0.38 Ti occupancy corresponding in endmembers to 45% p.f.u.) in two samples from Estima, magnesiodumortierite, 37% dumortierite, 5% Mozambique (Grew, 2002). There are two (Mg0.5Ti0.5)Al6BSi3O18, 5% of an Fe endmember mechanisms for incorporation of Ti in the and 7% &Al6BSi3O15(OH)3, i.e. magnesiodu- dumortierite group. In dumortierite containing mortierite is dominant whether Fe is ferrous or <0.06 (Mg + Fe2+) per formula unit, incorporation ferric. However, the calculated proportions are of Ti fits an empirical relationship 0.5Ti ? [6]Al sensitive to the assumed OH content, e.g. for OH (Grew, 2002), which suggests that the substitution
2832 DUMORTIERITE SUPERGROUP NOMENCLATURE
inferred for incorporation of Ti in the holtite magnesiodumortierite’’ component with Mg at group, 0.75Ti + 0.25&?Al at Al1 to form the the Al4 site unique to the Dora Maira locality. Ti analogue of holtite (Table 1; Fig. 5), could also The only substitutions reported at the Si sites contribute to Ti incorporation in the dumortierite (except As and Sb, see below) involve Al3+ and group, i.e. incorporation of the Ti analogue of P5+, reaching 0.17 Al and 0.09 P per formula unit holtite in dumortierite if Ti > (Mg+Fe2+) (Grew, 2002; Fuchs et al., 2005), much less than (Fig. 3b). However, it is doubtful that this the 0.49–0.51Al reported in dumortierite synthe- substitution would be relevant for dumortierite sized at 3À5 kbar via the substitution Si1,2Al + H containing more Mg and Fe2+. In this case, ? Si1,2Si (Werding and Schreyer, 1990). incorporation of Ti + (Mg, Fe2+) for 2Al at the However, incorporation of Al and P at the Si Al1 site (Table 1, Fig. 3a) is more plausible; this sites could involve other constituents in natural substitution was cited to explain the large Ti dumortierite. contents in magnesiodumortierite, which reach Dumortierite-group minerals commonly 4.28 wt.% TiO2 or 0.30 Ti p.f.u. (Chopin et al., contain Ta, Nb, As and Sb, and locally, Bi, all 1995; Ferraris et al., 1995). This Ti-rich of which represent solid solution with holtite- magnesiodumortierite is one of the few examples group minerals and szklaryite. Thus, calculation of a dumortierite-supergroup mineral in which of the proportion of vacancies at the Al1 site constituents other than Al have also been reported attributed to ‘‘hydroxydumortierite’’ must be at the Al2, Al3 or Al4 sites. Magnesium is corrected for vacancies contributed by these four interpreted to be incorporated at the Al4 site by constituents, as well as by Ti not associated with the substitution Al4Mg + OH ? Al4Al + O, Mg and Fe2+ in the component 2+ reaching about 50% replacement of Al. The ([Mg,Fe ]0.5Ti0.5)Al6BSi3O18. The role of Bi, structural formula deduced by these authors, presumed to be Bi3+, remains unclear because it
(Mgˆ ¯Tiˆ ¯&ˆ ¯)(Al0.5Mg0.5)2Al4BSi3O16(OH)2,is may be too large for the (As, Sb)-like sites, and not a valid endmember because more than one could instead substitute for Al3+ at the Al1 site site has multiple occupancy (Hawthorne, 2002). It (Groat et al., 2012). can be split into three endmembers: 16.7% No other constituent has been reported in (Mg0.5Ti0.5)Al6BSi3O18, 33.3% &Al6BSi3O15 amounts of >0.1 wt.% and usually mostly well (OH)3 and 50% (Mg0.5Ti0.5)Mg2 Al4 B below, e.g. Be, F, Na, K, Ca, Cr, Mn and Zr Si3O16(OH)2,wherethelastisa‘‘titano- (Grew, 2002; Fuchs et al., 2005; Groat et al., 2012).
Holtite group There are now three minerals in the holtite group, holtite, endmember composition (Ta0.6&0.4)Al6 BSi3 O 18, nioboholtite (IMA 2012-68), endmember composition (Nb0.6&0.4)Al6BSi3O18, and titanoholtite (IMA 2012-69), endmember composition (Ti0.75&0.25)Al6BSi3O18 (Fig. 5); the latter two minerals are described in Pieczka et al. (2013). Figure 3 shows that the basis for recognizing the holtite group is valency-imposed double site-occupancy in which Ta5+,Nb5+ and Ti4+ are paired with & in proportions to give a total valence of 3, whereas Fig. 5 shows that division within the group is based on the dominant-valency rule. FIG. 5. Subdivision of the holtite group into one Iron contents are generally small, not recognized mineral, holtite, and two new minerals, exceeding 0.77 wt.% FeO in dumortierite-super- nioboholtite (2012-68) and titanoholtite (2012-69), on group minerals at Szklary (Pieczka et al.,2011) the basis of Al1 occupancy. Ti = (Mg,Fe2+) is deducted and generally less, whereas MgO contents are from total Ti to obtain the amount of Ti in the holtite negligible. Thus, the most abundant component group. in dumortierite-group minerals would be
2833 A. PIECZKA ET AL.
4+ AlAl6 BSi3 O 18, with subordinate 3Si can be dominant at Al1 in some composi- 3+ 3+ 4+ &Al6BSi3O15(OH)3 contributing the OH found tions for which (As +Sb )
2834 DUMORTIERITE SUPERGROUP NOMENCLATURE
TABLE 2. Compositional variables used for plotting.
Mineral Ti > (Mg +Fe2+) Ti < (Mg +Fe2+)
——— Dumortierite group ——— Dumortierite Al1Al Al1Al Fe3+ analogue of dumortierite Fe3+ Fe3+ Magnesiodumortierite ——— MgÀTi*[Mg/(Mg + Fe2+] Fe2+ analogue of dumortierite ——— Fe2+ÀTi*[Fe2+/(Mg + Fe2+] Mg-Ti analogue of dumortierite 2Mg 2Ti*[Mg/(Mg + Fe2+] Fe2+-Ti analogue of dumortierite 2Fe2+ 2Ti*[Fe2+/(Mg + Fe2+] } { 2+ { ‘‘Hydroxydumortierite’’ ˆ ¯(OH) ˆ ¯(OHÀ[Mg+Fe ÀTi]) ——— Holtite group{ ——— Holtite ˙ ¯Ta ˙ ¯Ta Nioboholtite ˙ ¯Nb ˙ ¯Nb 2+ Titanoholtite ˘ ¯(TiÀMgÀFe )—— ——— Potential group{ ——— 3+ 3+ Szklaryite ˆ ¯As ˆ ¯As 3+ 3+ Sb analogue of szklaryite ˆ ¯Sb ˆ ¯Sb
Bold À Mineral approved by the IMA Commission. } OH was assumed to be absent in the compositions plotted in Fig. 7. { Amount of vacancy introduced at Al1 by the addition of these constituents. { Vacancy introduced at Al1 is included in the quantities of these constituents.
compositions plotted in Fig. 7a). A second Fe is Fe2+ in dumortierite (Pieczka, 2010; Pieczka simplifying assumption is that the difference et al., 2011). between total cations and the maximum possible, In the cases of minerals in the dumortierite 11 p.f.u., gives the vacancy at Al1; other sites are supergroup containing substantial Ta, Nb, As, Sb presumed to be fully occupied. In the absence of and/or Bi, the situation is more complex. We spectroscopic information, Fe valence must be recommend a modification of the approach assumed, but associated minerals could provide adopted by Pieczka et al. (2011) based on a guidance, e.g. association with minerals simplified version of the formula derived by Groat containing only Fe2+ is strong reason to presume et al. (2009). Assuming 1.000 B p.f.u. and the
FIG. 6. Diagram of the dumortierite-supergroup showing the constituents used to plot compositions for determining group and species.
2835 A. PIECZKA ET AL.
FIG. 7. Plots of selected dumortierite-supergroup minerals from the Szklary pegmatite (Pieczka et al., 2011) in the ternary system for the three groups in the dumortierite supergroup (a); and in the ternary system for the holtite 2+ group (b). The dumortierite-group component with Fe0.5Ti0.5 is deducted from total Ti to get the amount of Ti present as titanoholtite. Symbols: & À (As+Sb)-bearing dumortierite; & À szklaryite and dumortierite approaching szklaryite in composition; *,* and holtite, nioboholtite and titanoholtite, respectively; ~ À the Sb-richest holtite; ^ À type holtite (Pryce, 1971); À holtite H1, H2, H3 and H4 from Groat et al. (2009).
absence of OH, then these authors’ formula formulae in good agreement with site populations simplifies to Al7À(5x+4w+y)/3(Ta,Nb)xTiw determined in the structure refinements. &(2x+w+y)/3BSi(3Ày)(Sb,As)yO18Ày,i.e.analyses The recommended procedure for obtaining a should be normalized on the basis of O = formula of a dumortierite-supergroup mineral (18ÀAs–Sb) a.p.f.u. Vacancies have not been from an electron microprobe analysis is as reported at the Si or (As,Sb) sites, but normalizing follows: formulae by assuming Si + P + As + Sb = (1) Calculate a formula on the basis of O = (18– 3 a.p.f.u. is not recommended despite the iteration As–Sb) or O = (18–As–Sb–Bi), if Bi3+ is present involved, because [4]Al can substitute for Si not (2) Assume B is stoichiometric at 1 B p.f.u. only in dumortierite, but also in some holtite (3) Ideally, Si+P+As+Sb = 3, filling the Si1 and (Groat et al., 2009). Assuming OH is absent is a Si2 sites or their As3+ and Sb+3 equivalents. In major simplification of holtite composition cases where the sum Si+P+As+Sb < 3 a.p.f.u., add because FTIR spectra clearly show its presence Al to get Si+P+As+Sb+IVAl = 3 a.p.f.u. in samples from Greenbushes, Australia and (4) Assume Al2, Al3 and Al4 are fully Szklary (Groat et al., 2009), whereas Voloshin occupied by Al, for a total of 6 Al p.f.u. Only in et al. (1977, 1987) reported infrared evidence for magnesiodumortierite has another cation been H2O and OH in holtite from Voron’i Tundra, reported at these sites. Russia. Moreover, incorporation of IVAl could (5) Remaining Al, i.e. SAl-IVAl-6Al, is assigned require incorporation of OH for charge balance, as to Al1, together with Mg, Ti, Fe, Nb and Ta in the case of dumortierite (Werding and (6) If Nb and Ta are very subordinate at Al1, it Schreyer, 1990), as would incorporation of is likely the mineral contains significant OH; the (Mg,Fe2+) in excess of Ti. Nonetheless, we formula should recalculated on a different basis, think the assumption of negligible OH content is e.g. O = (17.625–As–Sb) to allow for 0.75 OH justified, because Groat et al. (2009) reported that p.f.u. (Moore and Araki, 1978). charge-balance calculations based on their single- (7) Iron valence could be estimated from crystal structure refinements give results consis- context, e.g. valence of Fe in associated minerals tent with essentially no water being present. In (8) If Fe is assumed to be trivalent, then it is 3+ other words, assuming holtite is anhydrous gives present as the Fe Al6BSi3O18 endmember
2836 DUMORTIERITE SUPERGROUP NOMENCLATURE
(9) If Fe is assumed to be divalent and Ti 4 indiscriminately to an ever-widening composi- (Fe2+ + Mg), combine the divalent components tional range, while dumortierite was found to 2+ with Ti to form (Fe0.5Ti0.5)Al6BSi3O18 and contain substantial amounts of the elements that (Mg0.5Ti0.5)Al6BSi3O18 and the excess Mg and supposedly distinguish holtite from dumortierite. 2+ Fe are present as MgAl6BSi3O17(OH) and Compositions of holtite show only crude 2+ 5+ 5+ 4+ Fe Al6BSi3O17(OH), respectively. If significant correlation between Ta or Nb (or Ti )on amounts of these components are present, the the one hand and Sb3+ and As3+ on the other. That formula should be calculated on a new O basis, this correlation is not well defined is a second allowing for additional OH with Mg and Fe2+. rationale for recognizing a new group in the new (10) If Ti 5 (Fe2+ + Mg), then include Ti in classification, i.e. distinguishing vacancies at the 2+ 3+ excess of (Mg + Fe ) as (Ti0.75&0.25)Al6BSi3O18 Al1 site introduced without (Sb,As) ? Si (11) Steps 5, 8, 9 and 10 will give the relative (holtite group) and vacancies introduced with proportion of the endmembers, which can be used (Sb,As)3+ ? Si (new group). to plot in Fig. 3 or 6 to identify group, then in Thirteen endmembers are needed to account for Fig. 4 or 5 to identify species. variations in the major constituents in the Analysis 4, Sz34/54, from Pieczka et al. (2011) minerals of the dumortierite supergroup. can serve as an example of this procedure. The calculated formula is: Acknowledgements (&0.37Al0.24Ti0.31Nb0.04Ta0.03Fe0.01)S1.00Al6B (Si2.29Sb0.51As0.19Al0.01)S3.00 (O17.30&0.70)S18.00 We thank Jan Kihle and Diederik Visser for Given the relatively large Ti and small Mg and unpublished analyses of dumortierite and Andrew Fe content, OH is assumed to be 0 and the Locock for a draft of the tetrahedron in Fig. 4 formula was calculated for O = 18–Sb–As = (adapted from Grew et al., 2013). Members of the 17.30. Si > (As + Sb), so the mineral is in the IMA CNMNC and two anonymous reviewers are dumortierite or holtite group. Rearranging the thanked for their comments on earlier versions of contents at the Al1 in terms of the endmembers this manuscript. ESG is supported by US National and assuming Fe is ferrous, we get in decreasing Science Foundation grant EAR 0837980 to the abundance: Al1 = {(Ti0.30&0.10)(Al0.24)(&0.22) University of Maine; AP is supported by AGH 2+ (Nb0.04&0.03)(Ta0.03&0.02) (Fe0.01Ti0.01)}S1.00 UST grant no 11.11.140.319; RJE and LAG by an That is: 40% (Ti0.75&0.25)Al6BSi3O18, 24% NSERC Discovery grant to LAG; GRR by NSF 3+ AlAl6BSi3O18, 17% &Al6BSb3 O15,6% grant EAR-0947956. 3+ &Al6BAs3 O15, 7% (Nb0.6&0.4)Al6BSi3O18,5% (Ta & )Al BSi O and 2% (Fe2+ Ti ) 0.6 0.4 6 3 18 0.5 0.5 References Al6BSi3O18, S = 101%. Allowing for the dominant valency rule, whereby the two endmem- Alexander, V.D., Griffen, D.T. and Martin, J.T. (1986) bers with & and R5+ at Al1 must be considered Crystal chemistry of some Fe- and Ti-poor together (Hatert and Burke, 2008), the dumortierites. American Mineralogist, 71, 786À794. Applin, K.R. and Hicks, B.D. (1987) Fibers of (Ti0.75&0.25)Al6BSi3O18 component is dominant, and the mineral is titanoholtite. dumortierite in quartz. American Mineralogist, 72, 170À172. Bertrand, E. (1880) Sur un mine´ral bleu de Chaponost, Summary of conclusions and pre`s Lyon. Sur un autre mine´ral bleu du Chili. recommendations Bulletin de la Socie´te´ Franc¸aise de Mine´ralogie, 3, 171À172. We recommend a classification based on the Borghi, A., Cossio, R., Fiori, L., Olmi, F. and Vaggelli, octahedral Al1 site with three hierarchal levels: a G. (2004) Chemical determination of colored zoned dumortierite supergroup which comprises the minerals in ‘natural stones’ by EDS/WDS electron dumortierite and holtite groups, plus a potential microprobe: an example from dumortierite quart- group not yet named, and six approved mineral zites. X-ray Spectrometry, 33,21À27. species, dumortierite, magnesiodumortierite, Cempı´rek, J. and Nova´k, M. (2005) A green dumortier- holtite, nioboholtite, titanoholtite and szklaryite. ite from Kutna´ Hora region, Czech Republic: A new classification of the dumortierite group spectroscopic and structural study. Crystallization is necessitated by the blurring of the distinction Processes in Granitic Pegmatites. Elba, Italy,4À5. between holtite and dumortierite, a situation Cempı´rek, J., Nova´k, M., Dolnı´cˇek, Z., Kotkova´, J. and arising from the term holtite being applied Sˇkoda, R. (2010) Crystal chemistry and origin of
2837 A. PIECZKA ET AL.
grandidierite, ominelite, boralsilite, and werdingite near-edge structure (ELNES) of the B K edge. from the Bory Granulite Massif, Czech Republic. American Mineralogist, 80, 1132À1144. American Mineralogist, 95, 1533À1547. Golovastikov, N.I. (1965) The crystal structure of Chopin, C., Klaska, R., Medenbach, O. and Dron, D. dumortierite. Doklady Akademii Nauk SSSR, 162, (1986) Ellenbergerite, a new high-pressure 1284À1287 (in Russian, English translation, Soviet MgÀAlÀ(Ti,Zr)-silicate with a novel structure based Physics Doklady, 10, 493À495). on face-sharing octahedra. Contributions to Gonnard, M.F. (1881) Note sur l’existence d’une espe`ce Mineralogy and Petrology, 92, 316À321. mine´rale nouvelle, la dumortie´rite dans le gneiss de Chopin, C., Ferraris, G., Ivaldi, G., Schertl, H.-P., Beaunan, au-dessus des anciens aqueducs gallo- Schreyer, W., Compagnoni, R., Davidson, C. and romains de la valle´e de l’Izeron (Rhoˆne). Bulletin de Davis, A.M. (1995) Magnesiodumortierite, a new la Socie´te´ Franc¸aise de Mine´ralogie, 4,2À5. mineral from very-high-pressure rocks (western Goreva, J.S. and Rossman, G.R. (2000) A blue variety of Alps). II. Crystal chemistry and petrological sig- rose quartz. Geological Society of America Abstracts nificance. European Journal of Mineralogy, 7, with Programs, 32(7), A-439 À A-440. 525À535. Goreva, J.S., Ma, C. and Rossman, G.R. (2001) Fibrous Claringbull, G.F. and Hey, M.H. (1958) New data for nanoinclusions in massive rose quartz: The source of dumortierite. Mineralogical Magazine, 31, rose coloration. American Mineralogist, 86, 901À907. 466À472. Evans, R.J. and Groat, L.A. (2012) Structure and Grew, E.S. (2002) Borosilicates (exclusive of tourma- topology of dumortierite and dumortierite-like line) and boron in rock-forming minerals in materials. The Canadian Mineralogist, 50, metamorphic environments. Pp. 387À502 in: 1197À1231. Boron: Mineralogy, Petrology, and Geochemistry Evans, R.J., Fyfe, C.A., Groat, L.A. and Lam, A.E. (L.M. Anovitz and E.S. Grew, editors). Reviews in (2012) MAS NMR measurements and ab initio Mineralogy, 33, Mineralogical Society of America, calculations of the 29Si chemical shifts in dumortier- Washington, D.C. ite and holtite. American Mineralogist, 97, 329À340. Grew, E.S., Locock, A.J., Mills, S.J, Galuskina, I.O., Farges, F., Galoisy, L., Balan, E., Fuchs, Y. and Linare`s, Galuskin, E.V. and Ha˚ lenius, U. (2013) J. (2004) Structure and color of the Jack Creek Nomenclature of the garnet supergroup. American dumortierite (Montana, USA) using spectroscopic Mineralogist, 98, 785À811. approaches. Mitteilungen der O¨ sterreichischen Groat, L.A., Grew, E.S., Ercit, T.S. and Pieczka, A. Mineralogischen Gesellschaft, 149, 29. (2001): The crystal chemistry of dumortierite and Ferraris,G.,Ivaldi,G.andChopin,C.(1995) holtite, aluminoborosilicates with heavy elements. Magnesiodumortierite, a new mineral from very- Geological Society of America Abstracts with high-pressure rocks (Western Alps). Part I: Crystal Programs, 33(6), A-383. structure. European Journal of Mineralogy, 7, Groat, L.A., Grew, E. S., Evans, R.J., Pieczka, A. and 167À174. Ercit, T.S. (2009) The crystal chemistry of holtite. Fleet, M.E. and Muthupari, S. (2000) Boron K-edge Mineralogical Magazine, 73, 1033À1050. XANES of borate and borosilicate minerals. Groat, L.A., Evans, R.J., Grew, E.S. and Pieczka, A. American Mineralogist, 85, 1009À1021. (2012) Crystal chemistry of As and Sb-bearing Fuchs, Y., Balan, E., Farges, F., Linare`s, J. and Horn, A. dumortierite. The Canadian Mineralogist, 50, (2004) Fe and Ti in dumortierite: A FTIR, EPR, 855À872. Mo¨ssbauer and Fe/Ti K-edge XANES study. Lithos, Hatert, F. and Burke, E.A.J. (2008) The IMAÀCNMNC 73 (Supplement), S39. dominant-constituent rule revisited and extended. Fuchs, Y., Ertl, A., Hughes, J. M., Prowatke, S., The Canadian Mineralogist, 46, 717À728. Brandstaetter, F. and Schuster, R. (2005) Hawthorne, F.C. (2002) The use of end-member charge- Dumortierite from the Gfo¨hl unit: Lower Austria; arrangements in defining new mineral species and chemistry, structure, and infra-red spectroscopy. heterovalent substitutions in complex minerals. The European Journal of Mineralogy, 17, 173À183. Canadian Mineralogist, 40, 699À710. Galliski, M.A., Ma´rques-Zavalı´a, M.F., Lira, R., Hoskins, B.F., Mumme, W.G. and Pryce, M.W. (1989) Cempı´rek, J. and Sˇkoda, R. (2012) Mineralogy and Holtite, (Si2.25Sb0.75)B[(Al6(Al0.43Ta0.27&0.30) origin of the dumortierite-bearing pegmatites of O15(O,OH)2.25]: crystal structure and crystal chem- Virorco, San Luis, Argentina. The Canadian istry. Mineralogical Magazine, 53, 457À463. Mineralogist, 50, 873À894. Huijsmans, J.P.P., Barton, M. and van Bergen, M.J. Garvie, L.A.J., Craven, A.J. and Brydson, R. (1995) (1982) A pegmatite containing Fe-rich grandidierite, Parallel electron energy-loss spectroscopy (PEELS) Ti-rich dumortierite and tourmaline from the study of B in minerals: The electron energy-loss Precambrian, high-grade metamorphic complex of
2838 DUMORTIERITE SUPERGROUP NOMENCLATURE
Rogaland, S. W. Norway. Neues Jahrbuch fu¨r Pryce, M.W. (1971) Holtite: a new mineral allied to Mineralogie Abhandlungen, 143, 249À261. dumortierite. Mineralogical Magazine, 38,21À25. Kazantsev, S.S., Pushcharovsky, D.Yu., Pasero, M., Raade, G., Rømming, C. and Medenbach, O. (1998) Merlino, S., Zubkova, N.V., Kabalov, Yu.K. and Carbonate-substituted phosphoellenbergerite from Voloshin, A.V. (2005) Crystal structure of holtite I. Modum, Norway: description and crystal structure. Crystallography Reports, 50,42À47. Mineralogy and Petrology, 62,89À101. Kazantsev, S.S., Zubkova, N.V. and Voloshin, A.V. Schaller, W.T. (1905) Dumortierite. In Contributions to (2006) Refinement of composition and structure of Mineralogy from the U. S. Geological Survey, U.S. holtite I. Crystallography Reports, 51, 412À413. Geological Survey Bulletin, 262,91À120 (A portion 3+ 2+ Keller, P. (2001) Ekatite, (Fe ,Fe ,Zn)12 of this paper was published in American Journal of (OH)6[AsO3]6[AsO3,HOSiO3]2, a new mineral from Science, 169, 211À224) Tsumeb, Namibia, and its crystal structure. Vaggelli, G., Olmi, F., Massi, M., Giuntini, L., Fedi, M., European Journal of Mineralogy, 13, 769À777. Fiori, L., Cossio, R. and Borghi, A. (2004) Chemical Kihle, J. (1989) Polymetamorphic evolution of cordier- investigation of colored minerals in natural stones of ite-bearing metapelites of the Bamble-sector, commercial interest. Microchimica Acta, 145, Southern Norway. Unpublished Candidate of 249À254. Science Thesis, Department of Geology, University Visser, D. and Senior, A. (1991) Mg-rich dumortierite in of Oslo, 3 vol, 360 p (in Norwegian). cordierite-orthoamphibole-bearing rocks from the Ma, C., Goreva, J.S. and Rossman, G.R. (2002) Fibrous high-grade Bamble Sector, south Norway. nanoinclusions in massive rose quartz: HRTEM and Mineralogical Magazine, 55, 563À577. AEM investigations. American Mineralogist, 87, Voloshin, A.V. and Pakhomovskiy, Ya.A. (1988) 269À276. Mineralogy of Tantalum and Niobium in Rare- Moore, P.B. and Araki, T. (1978) Dumortierite, Metal Pegmatites. Nauka, Leningrad (in Russian). Si3B[Al6.75&0.25O17.25(OH)0.75]: a detailed structure Voloshin, A.V., Gordienko, V.V., Gel’man, Ye.M., analysis. Neues Jahrbuch fu¨ r Mineralogie Zorina, M.L., Yelina, N.A., Kul’chitskaya, Ye.A., Abhandlungen, 132, 231À241. Men’shikov, Yu.P., Polezhayeva, L.I., Ryzhova, Ono, A. (1981) Synthesis of dumortierite in the system R.I., Sokolov, P.B. and Utochkina, G.I. (1977) Al O -SiO -B O -H O. Journal of the Japanese 2 3 2 2 3 2 Holtite (first find in the USSR) and its relationship Association of Mineralogists, Petrologists and with other tantalum minerals in rare-metal pegma- Economic Geologists, 76(1), 21À25. tites. Zapiski Vsesoyuznogo Mineralogicheskogo Pieczka, A. (2010) Primary Nb-Ta minerals in the Szklary pegmatite, Poland: new insights into controls Obshchestva, 106(3), 337À347 (in Russian). of crystal chemistry and crystallization sequences. Voloshin, A.V., Pakhomovskiy, Ya.A. and Zalkind, American Mineralogist, 95, 1478À1492. O.A. (1987) An investigation of the chemical Pieczka, A. and Marszałek, M. (1996) Holtite À the first composition and IR-spectroscopy of holtite. In occurrence in Poland. Mineralogia Polonica, 27, Mineral’nyye Assotsiatsii i Mineraly 3À8. Magmaticheskikh Kompleksov Kol’skogo Pieczka, A., Grew, E.S., Groat, L.A. and Evans, R.J. Poluostrova, pp. 14À34 Kol’skiy Filial Akademii (2011) Holtite and dumortierite from the Szklary Nauk SSSR, Apatity (in Russian). Pegmatite, Lower Silesia, Poland. Mineralogical Vra´na, S. (1979) A polymetamorphic assemblage of Magazine, 75, 303À315. grandidierite, kornerupine, Ti-rich dumortierite, Pieczka, A., Evans, R.J., Grew, E.S., Groat, L.A., Ma, C. tourmaline, sillimanite, and garnet. Neues Jahrbuch and Rossman, G.R. (2013) The dumortierite super- fu¨r Mineralogie Monatshefte, 1979(1), 22À33. group. II. Three new minerals from the Szklary Werding, G. and Schreyer, W. (1990) Synthetic pegmatite, SW Poland: Nioboholtite, dumortierite: its PTX-dependent compositional var- (Nb0.6& 0.4)Al6 BSi3 O 18, titanoholtite, iations in the system Al2O3-B2O3-SiO2-H2O. (Ti0.75& 0.25)Al6 BSi3 O 18, and szklaryite, Contributions to Mineralogy and Petrology, 105, 3+ &Al6BAs3 O15 Mineralogical Magazine, 77, 11À24. 2841À2856. Willner, A.P. and Schreyer, W. (1991) A dumortierite- Platonov, A.N., Langer, K., Chopin, C., Andrut, M. and topaz-white mica fels from the peraluminous Taran, M.N. (2000) Fe2+-Ti4+ charge-transfer in metamorphic suite of Bushmanland (South Africa). dumortierite. European Journal of Mineralogy, 12, Neues Jahrbuch fu¨r Mineralogie Monatshefte, 521À528. 1991(5), 223À240.
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