• journal_title：Mineralogical Magazine
• Contributor：D. Atencio ; M. E. Ciriotti ; M. B. Andrade
• Publisher：Mineralogical Society of Great Britain and Ireland
• Date：2013-06-01
• Format：text/html
• Language：en
• Identifier：10.1180/minmag.2013.077.4.06
• journal_abbrev：Mineralogical Magazine
• issn：0026-461X
• volume：77
• issue：4
• firstpage：467
• section：Articles

Fluorcalcioroméite, (Ca,Na)₂ (O,OH)₆F, is a new roméite-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 ~5½, tenacity is brittle. Cleavage is not observed; fracture is conchoidal. The calculated density is 5.113 g/cm³. 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 (Ca_1.16Na_0.56□_0.22 )_Σ2.00( Al_0.01W_0.01)_Σ2.00O₆[F_0.62(OH)_0.28O_0.06□_0.04]_Σ1.00. The strongest eight X-ray powder-diffraction lines [d in Å(I)(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 (R₁ = 0.0106) gave the following data: cubic, Fd3İm, a = 10.2987(8) Å, V = 1092.31(15) ų, Z = 8. Unit-cell parameters refined from the powder data are: a = 10.284(2), V = 1087.7(7) ų, Z = 8.