Brizziite, NaSbO 3 , a new mineral from the Cetine Mine (Tuscany, Italy); description and crystal structure

Brizziite is a new sodium antimonate mineral from the Cetine mine, Tuscany, Italy. It occurs as dense aggregates of platy {001} hexagonal crystals. Associated minerals are stibiconite and mopungite. The crystals, which are polysynthetically twinned, are colourless and transparent, with pearly lustre. Electron microprobe analyses give Na 2 O 15.98 and Sb 2 O 5 83.28 wt.%, corresponding to the formula NaSbO 3 . Optically, brizziite is uniaxial (-) with e = 1.631(1), ω = 1.84, birefringence 0.21(1); VHN 15 microhardness 57; D meas = 4.8(2) g/cm 3 ; D calc = 4.95 g/cm 3 . The unit cell is rhombohedral (hexagonal) a = 5.301(1), c = 15.932(4) A, space group R3 and Z = 6