• journal_title：European Journal of Mineralogy
• Contributor：Werner KRAUSE ; Heinz-Jürgen BERNHARDT ; Herta EFFENBERGER ; Thomas WITZKE
• Publisher：E. Schweizerbart'sche Verlagsbuchhandlung Science Publishers
• Date：2002-
• Format：text/html
• Language：en
• Identifier：10.1127/0935-1221/2002/0014-0115
• journal_abbrev：Eur J Mineral
• issn：0935-1221
• volume：14
• issue：1
• firstpage：115
• section：Articles

Schneebergite and nickelschneebergite are new members of the tsumcorite group; they represent the bismuth analogues of cobaltlotharmeyerite and nickellotharmeyerite. The two minerals were discovered on samples from the former mining area “Am Roten Berg”, Schneeberg, Saxony, Germany; associated minerals are scorodite, barium-pharmacosiderite, ferrilotharmeyerite (cobaltoan, bismuthian), preisingerite, and waylandite. Schneebergite and nickelschneebergite are very similar in appearance; they form crystal aggregates up to 1 mm and small tabular crystals (≤ 0.5 mm), elongated parallel to [010]. The colour is brown to beige (depending on the iron content), the streak is pale brown; Vickers hardness is VHN₁₅ = 250 kg/mm² corresponding to a Mohs' hardness of 4 to 4 1/2. Crystallographic forms are {2̄01} (dominant), {001}, {101}, {1̄01}, {1̄02}, {1̄11}. The optical orientation is Y parallel to [010], X ≈ [001], pleochroism is weak to distinct (depending on the iron content) with X = Z = pale yellow and Y = brown (for both minerals). Schneebergite is biaxial positive, 2V = 85(5)°, n_x = 1.93(calc.), n_y = 1.95(1), and n_z = 1.98(2); nickelschneebergite is biaxial negative, 2V = 77(5)°, n_x = 1.92(calc.), n_y = 1.95(1), and n_z = 1.97(2). Empirical formulas calculated from electron microprobe analyses and based on 10 oxygen atoms are (Bi_0.74Ca_0.29)_Σ1.03(Co_1.06Ni_0.75Fe_0.22)_Σ2.03 [(AsO₄)1.99(SO₄)_0.01]_Σ2.00 [(OH)_1.09(H₂O)_0.91]_Σ2.00 for schneebergite, and (Bi_0.73Ca_0.28Pb_0.01)_Σ1.02 (Ni_1.18Co_0.64Fe_0.16)_Σ1.98 (AsO₄)_1.99 [(H₂O)_1.10(OH)_0.93]_Σ2.03 for nickelschneebergite; the ideal formulas are BiCo₂(AsO₄)₂[(H₂O)(OH)] and BiNi₂(AsO₄)₂ [(H₂O)(OH)], respectively. There is a probably complete solid solution involving schneebergite, nickelschneebergite, cobaltlotharmeyerite, and nickellotharmeyerite. Schneebergite/nickelschneebergite are monoclinic, space group C2/m, with a = 9.005(1)/8.995(1), b = 6.211(1)/6.207(1), c = 7.440(1)/7.462(1) Å, β = 115.19(1)/115.00(1)°, V = 376.5(1)/377.6(1) ų, Z = 2, D_calc = 5.28/5.23 g/cm³. Structure investigations for schneebergite (R1 = 0.038) and nickelschneebergite (R1 = 0.044) based on single-crystal X-ray data confirmed isotypy with the tsumcorite-type structure.