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American Mineralogist; April 2006; v. 91; no. 4; p. 584-588; DOI: 10.2138/am.2006.2033
© 2006 Mineralogical Society of America
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Poppiite, the V3+ end-member of the pumpellyite group: Description and crystal structure

Maria Franca Brigatti1,*, Enrico Caprilli1 and Marco Marchesini2

1 Dipartimento di Scienze della Terra, Università di Modena e Reggio Emilia, Largo S. Eufemia 19, I-41100 Modena, Italy
2 ENI-AGIP Towers, I-20097 San Donato Milanese, Italy

Correspondence: * E-mail: brigatti{at}unimore.it

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){sum}8.00[VI](V3+1.26 Fe3+1.02 Mg0.78 Mn2+0.59 Al0.31 Cu2+ 0.04){sum}4.00 [VI](V3+ 6.89 Al1.07 Ti0.04){sum}8.00 [IV](Si11.69Al0.31){sum}12.00 O42 (OH)14; C2/m, a = 19.2889(6), b = 6.0444(2), c = 8.8783(3) Å, ß = 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, (Formula13); 2.551, 62, (420); 1.612, 57, (Formula31,424); and 2.367, 51, (222, 403). Poppiite is optically negative, with 2Vcalc = 44°, n{alpha} = 1.768(9), nß 1.804(8), n{gamma} 1.810(9). The pleochroic scheme is {alpha} = light yellowish brown, ß = deep greenish brown, and {gamma} = 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.

Key Words: New mineral • analysis chemical (mineral) • crystal structure • optical properties • XRD data




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