Abstract
The minerals hentschelite and reichenbachite have been found as secondary minerals in a silicified barite vein at Reichenbach, Odenwald, Germany. They occur as dark green translucent crystals with a light green streak. Both minerals are nonfluorescent; they have no cleavage, a vitreous luster, and a hardness about 3.5. The analytical formula for hentschelite, based on 18 negative charges, is Cu1.03(Fe1.87Al0.l2)Σ1.99(P1.92As0.08)Σ2.00O8(OH)2, and the idealized formula is CuFe2(PO4)2(OH)2. Hentschelite is monoclinic, P21/n, with a = 6.984(3) Å, b = 7.786(3) Å, c = 7.266(3) Å,β = 117.68(2)°, Z = 2, and Dcalc = 3.79 g/cm3 for the ideal formula. The axial ratio a:b:c = 0.8970:1:0.9332. The strongest lines in the X-ray powder-diffraction pattern are (d(Å),I,hkl) 4.81(50)(lll), 3.33(100)(111,021), 3.27(50)(112,121), 3.06(20)(202), 2.400(20)(031,222,130), 2.112(20)(132), 1.669(20)(222,042), and 1.648(20)(224). The mineral is biaxial positive with α = 1.843(3), β = 1.848(3), and γ = 1.945(3) (λ = 589 nm). The orientation is Y = b, X ≈ [101]; 2Vobs is small; and axial dispersion is strong with r ≫ v.
The analytical formula for reichenbachite, based on 20 negative charges, is Cu5.07(P1.86As0.11Si0.01)Σ1.98O8(OH)4, and the theoretical formula is Cu5(Po4)2(OH)4. Reichenbachite is monoclinic, P21/a, with a = 9.198(3) Å, b= 10.691(3) Å, c = 4.476(2) Å, β = 92.42(2)°, Z = 2, and Dcalc = 4.35 g/cm3 for the ideal formula. The axial ratio a:b:c = 0.8603:1:0.4187. The strongest lines in the X-ray powder-diffraction pattern are (d(Å),I,hkl) 4.470(100)(001), 3.132(30)(211), 3.012(30)(211), 2.945(20)(310), 2.814(25)(230), 2.410(100)(311,231), 2.357(20)(231), 2.238(20)(141), and 2.235(20)(002). The mineral is biaxial negative with α = 1.782(2), βcalc = 1.833, γ = 1.867(5) (λ = 589 nm); 2Vobs = 76.3(4)° (from extinction curves). The orientation is Y = b, Z Λ a = 29° (in the obtuse angle of β), and dispersion is weak with r < v.
