Poppiite, the V3+ end-member of the pumpellyite group: Description and crystal structure
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Maria Franca Brigatti
,
Enrico Caprilli
Abstract
Poppiite, a new mineral from Gambatesa mine (Val Graveglia, Genova, Northern Italy), is the V3+ end-member of the pumpellyite group [[VII](Ca7.68 Na0.27 K0.03 Rb0.02)Σ8.00[VI](V3+1.26 Fe3+1.02 Mg0.78 Mn2+0.59 Al0.31 Cu2+0.04)Σ4.00[VI](V3+6.89 Al1.07 Ti0.04)Σ8.00[IV](Si11.69Al0.31)Σ12.00 O42 (OH)14; C2/m, a = 19.2889(6), b = 6.0444(2), c = 8.8783(3) Å, β = 97.328(2)°, V = 1026.66(6) Å3, Dmeas = 3.36(2) g/cm3, and Dcalc = 3.44 g/cm3]. Poppiite crystals, with size varying from 0.1 to 0.6 mm, are minute, greenish-brown, and prismatic, and are associated with roscoelite, ganophyllite, manganaxinite, goldmanite, and calcite. The strongest lines in the X-ray powder diffraction pattern [dobs (Å), Irel, (hkl)] are: 2.930, 100, (511); 3.817, 70, (202); 2.548, 65, (3.13); 2.551, 62, (420); 1.612, 57, (7.31,424); and 2.367, 51, (222, 403). Poppiite is optically negative, with 2Vcalc = 44°, nα = 1.768(9), nβ 1.804(8), nγ 1.810(9). The pleochroic scheme is α = light yellowish brown, β = deep greenish brown, and γ = brown to reddish brown. The crystal structure was refined using 1918 unique reflections to R = 0.0307. Like the other pumpellyite-group minerals the crystal structure of poppiite consists of chains of edge-sharing octahedra linked by SiO4, Si2O7, and CaO7 polyhedra
© 2015 by Walter de Gruyter Berlin/Boston
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- Electron-beam (5–10 keV) damage in triplite-group phosphates: Consequences for electron-microprobe analysis of fluorine
- Vacancy defects in MgO at high pressure
- Plastic flow of pyrope at mantle pressure and temperature
- Parvo-mangano-edenite, parvo-manganotremolite, and the solid solution between Ca and Mn2+ at the M4 site in amphiboles
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