Strontiomelane, SrMn64+Mn23+O16, a new mineral species of the cryptomelanegroup from St. Marcel Praborna, Aosta Valley, Italy

Strontiomelane is a new mineral species from the Praborna mine near Saint-M arcel, Aosta Valley, Italian Alps. It occurs as small anhedral inclusions ( about 100-200 mu m) and veinlets associated with braunite, cryptomelane, ho llandite, quartz, fluorapatite, titanite, jadeite and strontiopiemontite. T he new species is opaque. black with a submetallic luster and a strong grey -white pleochroism: in plane-polarized light in oil immersion, it presents a medium anisotropy with grey-blue ro white tints. Strontiomelane, whose id eal formula is SrMn64+Mn23+O16, crystallizes in space group P2(1)/n (14) wi th a 10.00(1), b 5.758(7), c 9.88(1) Angstrom, beta 90.64(6)degrees and Z = 2. The strongest lines in the X-ray powder pattern [d in Angstrom(I)(hkl)] are: 3.15(100)(103), 3.13(80)(103), 2.409(80)(122), 2.170(60)(320) and 1.5 56(50)(225). The calculated density is 4.66(1)g.cm(-3). Strontiomelane is t he Sr end-member of the cryptomelane group. The proposed name is derived fr om the chemical element strontium and the color black, melas,- anos in Gree k.