• journal_title：The Canadian Mineralogist
• Contributor：Stanislav K. Filatov ; Lidiya P. Vergasova ; Marina G. Gorskaya ; Sergey V. Krivovichev ; Peter C. Burns ; Vladimir V. Ananiev
• Publisher：Mineralogical Association of Canada
• Date：2001-
• Format：text/html
• Language：en
• Identifier：10.2113/gscanmin.39.4.1115
• journal_abbrev：Can Mineral
• issn：0008-4476
• volume：39
• issue：4
• firstpage：1115
• section：Articles

Bradaczekite, NaCu₄(AsO₄)₃, was discovered in a fumarole in the North Breach of the Great fissure Tolbachik eruption (GFTE) in 1975–1976, Kamchatka Peninsula, Russia. Bradaczekite forms aggregates of dark blue plates elongate along [1̅02]. The well-developed forms are {010}, {3̅11}, {111} and {1̅12}. The forms {3̅01}, {001}, {3̅21}, {1̅01}, {100}, {021}, {110}, {1̅31}, {1̅11} and {341} are common. Associated minerals are hematite, tenorite, lammerite, urusovite, orthoclase and johillerite. The mineral has an adamantine luster and a light blue to white streak. No cleavage has been observed. The mineral is transparent, biaxial, optically negative, α 1.76(1), β 1.92(1), γ 1.96(1), 2V_calc 50.0°. The optical orientation is Z = b, X ∧ c = 23° in the obtuse β angle. Bradaczekite shows strong pleochroism: X violet-red, Y green, Z greenish blue. The mineral is monoclinic, space group C2/c, a 12.051(1), b 12.434(1), c 7.2662(7) Å, β 117.942(1)°, V 961.8(2) ų, Z = 4, D_calc = 4.77(1) g/cm³ (for the empirical formula).The strongest eight lines of the X-ray powder-diffraction pattern [d in Å(I)(hkl)] are: 6.22(13)(020), 3.60(21)(2̅02, 1̅31), 3.43(100)(1̅12, 310), 3.21(35)(002), 2.791(24)(4̅02), 2.696(18)(330), 2.683(30)(240), and 2.665(17)(400). Electron-microprobe analyses yielded: Na₂O 5.17 (4.37–5.78), K₂O 0.35 (0.14–0.80), CuO 43.13 (41.31–45.22), ZnO 0.79 (0.19–1.18), Fe₂O₃ 0.38 (0.03–1.05), As₂O₅ 49.62 (48.61–50.66), V₂O₅ 0.13 (0–0.90), total 99.55 (97.69–101.56) wt.%. The empirical formula, normalized to O = 12 apfu (atoms per formula unit), is (Na_1.16K_0.05)_∑1.21(Cu_3.74Zn_0.07Fe³⁺_0.03)_∑3.84(As_3.00V_0.01)_∑3.01O₁₂, close to the ideal NaCu₄(AsO₄)₃ confirmed by crystal-structure analysis. The mineral is named in honor of Hans Bradaczek, crystallographer at the Free University of Berlin.