TUNGSTIBITE, SB2O3-CENTER-DOT-WO3 - A NEW MINERAL FROM THE CLARA MINE NEAR OBERWOLFACH IN THE CENTRAL BLACK-FOREST (GERMANY)

Tungstibite belongs to the mineral assemblage of the Clara Mine in the central Black Forest. It occurs on the gangue minerals quartz, barite and fluorite, occasionally also on fahlore and chalcopyrite, and is sometimes intergrown with cervantite. The mineral forms globular aggregates up to 1 mm in diameter composed of thin tabular crystals which are elongated parallel to one axis and sometimes spear-shaped. The plane of flattening is (001). Cleavage (001) perfect, fracture irregular, hardness about 2, D-x 6.90 g/cm(3), colour green to dark green, streak greenish, translucent to opaque, luster dull, in part also pearly. Optical data: n(alpha) 2.285 (20), n(beta) 2.40 (2), n(gamma) 2.58 (2), 2V calc. 82 degrees, r much less than v strong, pleochroism X dark green to brownish-green, Y dark green, Z pale green to yellowish, Z = c. Unit-cell dimensions: a(0) 8.59 (2), b(0) 9.58 (2), c(0) 6.12 (2) Angstrom, Z = 4. Probable space group: P22(1)2(1). Strongest lines of the powder pattern: 3.32 (10) 211; 3,06 (10) 002; 2.73 (6) 310; 2.46 (5) 122, 320. Result of analysis: Sb2O3 55.5, WO3 43.6%, total 99.1%, yielding on the basis of 6 oxygen atoms the empirical formula Sb-2.01 W-0.99 O-6 and simplified Sb2O3 . WO3. The lattice is stable up to a temperature of 600 degrees C. Synthesis of the mineral was performed by reaction of equivalent amounts of Sb2O3 and WO3 in the presence of H2O in a pressure vessel at 240 degrees C.