Xitieshanite—A new ferric sulphate mineral

Xitieshanite is a new ferric sulfate mineral discovered in the oxidation zone of a Pb-Zn deposit at Xitieshan, Qinghai Province, China. The typical crystal of xitieshanite is a rhombic rectangle. It is bright green in colour with a light yellow tint. Luster vitrous Translucent to almost transparent. Streak yellow. Cleavage imperfect. Fracture uneven or conchoidal. H. (Vickers)=62.6kg/mm². Specific gravity=1.99_obs(2.02_calc,) Pleochroism strong, and axial colours: X=colourless to pale yellow, Y=pale yellow, Z=light yellow with greenish tint. It is optically positive, biaxial, 2V=77°,r v. Refractive indices:N _x =1.536,N _y =1.570,N _z =1.628. Extinction parallel and inclined. Elongation positive and negative. X-ray single-crystal study shows it is monoclinic. Space groupP2₁/a. Unit cell parameters:a=14.102,b=6.908,c=10.673 Å, β=111.266°,V=968.9, ų,Z=4. The powder pattern of xitieshanite gave the strongest lines: 6.67(6)(201), 6.09(5)(110), 5.69(5)(011), 4.96(10)(002), 4.81(10)(211), 4.21(5)(112), and 3.90(9)(211). Chemical analysis gave Al₂O₃ 0.01, Fe₂O₃ 26.15, FeO 0.18, MgO 0.03, CaO 0.09, K₂O 0.03, Na₂O 0.07, SO₃ 27.69, H₂O 45.02, total 99.27%, corresponding to the chemical formula: Fe²⁺ (SO₄)(OH) · 7H₂O. The DTA curve shows respectively three strong endothermic peaks at 85°, 170°, and 735°C, and a weak peak at 460°C. The TGA curve shows a loss of weight in three different steps. The infrared spectral curve of xitieshanite demonstrates that it has two principal absorption bands at 3,350 and 1,225–1,003 cm^?1 and two subordinate bands at 1,620 and 603 cm^?1.