Fluorcalcioromeite, (Ca,Na)(2)Sb-2(5+)(O,OH)(6)F, a new romeite-group mineral from Starlera mine, Ferrera, Grischun, Switzerland: description and crystal structure

Autor(es)

Atencio, D. ^[1] ; Ciriotti, M. E. ^[2] ; Andrade, M. B. ^[3]

Afiliação do(s) autor(es)

^[1] Univ Sao Paulo, Dept Mineral & Geotecton, Inst Geociencias, BR-05508080 Sao Paulo - Brazil

^[2] Assoc Micromineral Italiana, I-10073 Devesi Cirie - Italy

^[3] Univ Arizona, Dept Geosci, Tucson, AZ 85721 - USA

• Tipo de documento: Artigo Científico
• Fonte: MINERALOGICAL MAGAZINE; v. 77, n. 4, p. 467-473, JUN 2013.
• Citações Web of Science: 6

Resumo

Fluorcalcioromeite, (Ca,Na)(2)Sb-2(5+)(O,OH)(6)F, is a new romeite-group, pyrochlore-supergroup mineral (IMA 2012-093), from Starlera mine, Ferrera, Hinterrhein district, Grischun, Switzerland. The intimately associated minerals are: braunite, hematite, calcite, quartz and, rarely, wallkilldellite-(Mn). It occurs as euhedral octahedra, untwinned, from 0.1 to 1 mm in size. The crystals are yellow to orange and translucent; the streak is white, and the lustre is vitreous to resinous. It is non-fluorescent under ultraviolet light. Mohs' hardness is similar to 5 1/2, tenacity is brittle. Cleavage is not observed; fracture is conchoidal. The calculated density is 5.113 g/cm(3). The mineral is isotropic, n(calc.) = 1.826. The Raman spectrum is dominated by bands of Sb-O octahedral bond stretching and O-Sb-O bending modes. The chemical composition (n = 13) is (by wavelength-dispersive spectroscopy (WDS), H2O calculated by difference, wt.%): Na2O 4.11, CaO 15.41, MnO 0.54, CuO 0.01, ZnO 0.01, PbO 0.02, Al2O3 0.10, FeO 0.50, Y2O3 0.07, SiO2 0.04, TiO2 0.01, UO2 0.01, Sb2O5 76.18, WO3 0.78, F 2.79, H2O 0.59, O = F -1.17, total 100.00. The empirical formula, based on 2 cations at the B site, is (Ca1.16Na0.56 square 0.22Fe0.032+Mn0.032+)(Sigma 2.00)(Sb1.985+Al0.01W0.01)Sigma O-2.00(6){[}F-0.62(OH)(0.28)O-0.06 square(0.04)](Sigma 1.00). The strongest eight X-ray powder-diffraction lines {[}d in angstrom(1)(hkl)] are: 5.934(81)(111), 3.102(20)(311), 2.969(100)(222), 2.572(6)(400), 1.979(7)(333), 1.818(8)(440), 1.551(15)(622), and 1.484(5)(444). The crystal structure refinement (R-1 = 0.0106) gave the following data: cubic, Fd (3) over barm, a = 10.2987(8) angstrom, V = 1092.31(15) angstrom(3), Z = 8. Unit-cell parameters refined from the powder data are: a = 10.284(2), V = 1087.7(7) angstrom(3), Z = 8. (AU)

• Processo FAPESP: 11/22407-0 - Caracterização de espécies minerais brasileiras novas e raras
• Beneficiário: Daniel Atencio
• Modalidade de apoio: Auxílio à Pesquisa - Regular
• Processo FAPESP: 08/04984-7 - Determinação e refinamento da estrutura cristalina de minerais do grupo de pirocloro
• Beneficiário: Marcelo Barbosa de Andrade
• Modalidade de apoio: Bolsas no Brasil - Pós-Doutorado