Szczegóły publikacji
Opis bibliograficzny
The dumortierite supergroup. [Pt.] 2, three new minerals from the Szklary pegmatite, SW Poland: nioboholtite, $(Nb_{0.6}\square_{0.4})Al_{6}BSi_{3}O_{18}$, titanoholtite, $(Ti_{0.75}\square_{0.25})Al_{6}BSi_{3}O_{18}$, and szklaryite, $\square Al_{6}BAs^{3+}_{3}O_{15}$ / A. PIECZKA, R. J. Evans, E. S. Grew, L. A. Groat, C. Ma, G. R. Rossman // Mineralogical Magazine ; ISSN 0026-461X. — 2013 — vol. 77 no. 6, s. 2841–2856. — Bibliogr. s. 2855–2856, Abstr.
Autorzy (6)
- AGHPieczka Adam
- Evans R. James
- Grew Edward S.
- Groat Lee A.
- Ma C.
- Rossman George R.
Słowa kluczowe
Dane bibliometryczne
| ID BaDAP | 79077 |
|---|---|
| Data dodania do BaDAP | 2014-01-22 |
| Tekst źródłowy | URL |
| DOI | 10.1180/minmag.2013.077.6.10 |
| Rok publikacji | 2013 |
| Typ publikacji | artykuł w czasopiśmie |
| Otwarty dostęp |  |
| Czasopismo/seria | Mineralogical Magazine |
Abstract
Three new minerals in the dumortierite supergroup were discovered in the Szklary pegmatite, Lower Silesia, Poland. Nioboholtite, endmember (Nb-0.6 square(0.4))Al6B3Si3O18, and titanoholtite, endmember (Ti-0.75 square(0.25))Al6B3Si3O18, are new members of the holtite group, whereas szklaryite, endmember square Al6BAs33+O15, is the first representative of a potential new group. Nioboholtite occurs mostly as overgrowths not exceeding 10 mu m in thickness on cores of holtite. Titanoholtite forms patches up to 10 mu m across in the holtite cores and streaks up to 5 mu m wide along boundaries between holtite cores and the nioboholtite rims. Szklaryite is found as a patch similar to 2 mu m in size in As- and Sb- bearing dumortierite enclosed in quartz. Titanoholtite crystallized almost simultaneously with holtite and other Ta-dominant minerals such as tantalite-(Mn) and stibiotantalite and before nioboholtite, which crystallized simultaneously with stibiocolumbite during decreasing Ta activity in the pegmatite melt. Szklaryite crystallized after nioboholtite during the final stage of the Szklary pegmatite formation. Optical properties could be obtained only from nioboholtite, which is creamy-white to brownish yellow or grey-yellow in hand specimen, translucent, with a white streak, biaxial (-), n(alpha) = 1.740-1.747, n(beta) similar to 1.76, n(gamma) similar to 1.76, and Delta < 0.020. Electron microprobe analyses of nioboholtite, titanoholtite and szklaryite give, respectively, in wt.%: P2O5 0.26, 0.01, 0.68; Nb2O5 5.21, 0.67, 0.17; Ta2O5 0.66, 1.18, 0.00; SiO2 18.68, 21.92, 12.78; TiO2 0.11, 4.00, 0.30; B2O3 4.91, 4.64, 5.44; Al2O3 49.74, 50.02, 50.74; As2O3 5.92, 2.26, 16.02; Sb2O3 10.81, 11.48, 10.31; FeO 0.51, 0.13, 0.19; H2O (calc.) 0.05, -, Sum 96.86, 96.34, 97.07, corresponding on the basis of O = 18 As-Sb to {(Nb0.26Ta0.02 square(0.18)) (Al0.27Fe0.05Ti0.01)square(0.21)}(Sigma 1.00)Al6B0.9{Si2.03P0.02(Sb0.48As0.39Al0 07}(Sigma 3.00)(O17.09OH0.04 square(0.87))(Sigma 18.00), {(Ti0.32Nb0.03Ta0.03 square(0.10))(Al0.35Ti0.01Fe0.01)square(0.15)}(Sigma 1.00)Al6B0.86{Si-2.36(Sb0.51As0.14)}(Sigma 3.01) (O-17.35 square(0.65))(Sigma 18.00) and {square(0.53)(Al0.41Ti0.02Fe0.02)(Nb-0.01 square(0.01))Sigma 1.00Al6B1.01{(As1.07Sb0.47Al0.03) Si1.37P0.06}(Sigma 3.00)(O-16.46 square(1.54))(Sigma 18.00). Electron backscattered diffraction indicates that the three minerals are presumably isostructural with dumortierite, that is, orthorhombic symmetry, space group Pnma (no. 62), and unit-cell parameters close to a = 4.7001, b = 11.828, c = 20.243 angstrom, with V = 1125. 36 angstrom(3) and Z = 4; micro-Raman spectroscopy provided further confirmation of the structural relationship for nioboholtite and titanoholtite. The calculated density is 3.72 g/cm(3) for nioboholtite, 3.66 g/cm(3) for titanoholtite and 3.71 g/cm(3) for szklaryite. The strongest lines in X-ray powder diffraction patterns calculated from the cell parameters of dumortierite of Moore and Araki (1978) and the empirical formulae of nioboholtite, titanoholtite and szklaryite are [d, angstrom, I (hkl)]: 10.2125, 67, 46, 19 (011); 5.9140, 40, 47, 57 (020); 5.8610, 66, 78, 100 (013); 3.4582, 63, 63, 60 (122); 3.4439, 36, 36, 34 (104); 3.2305, 100, 100, 95 (123); 3.0675, 53, 53, 50 (105); 2.9305, 65, 59, 51(026); 2.8945, 64, 65, 59 (132), respectively. The three minerals have been approved by the IMA CNMNC (IMA 2012-068, 069, 070) and were named for their relationship to holtite and occurrence in the Szklary pegmatite, respectively.
