Belogubite, a new mineral of the chalcanthite group from the Gayskoe deposit, South Urals, Russia

Abstract

Belogubite, ideally CuZn(SO 4 ) 2 ·10H 2 O, has been found in the supergene zone uncovered by the open pit at the Gayskoe massive sulfide Zn-Cu deposit (Orenburgskaya region, the South Urals, Russia). It is associated with dietrichite and may contain relics of quartz. Belogubite forms aggregates of blue grains up to 1 mm in size. The mineral is transparent with vitreous luster and white streak. Its color varies from pale equant to light blue. Cleavage and parting were not observed. The new mineral is brittle and has Mohsʼ hardness  ca . 2½. Its density measured by floatation in bromoform+ethanol is 2.27(2) g/cm –3 , its calculated density is 2.249 g/cm –3 . Belogubite is biaxial (–), α = 1.512(2), β = 1.525(2), γ = 1.531(2); 2 V  (meas.) = 70(10)°, 2 V  (calc.) = 67.9°. Dispersion is noticeable,  r  <  v . The mineral is nonpleochroic. Chemical composition of the holotype sample is (wt %, electron microprobe data, H 2 O determined by thermogravimetry): MgO 1.12, MnO 0.10, FeO 3.15, CuO 8.98, ZnO 18.02, SO 3  32.49, H 2 O 36.75, total 100.61. Its empirical formula calculated on the basis of 18 O  apfu  is: (Cu 0.55 Zn0 .45 ) Σ1.00 (Zn 0.64 Fe 0.22 Mg 0.14 Mn 0.01 ) Σ1.01 S 1.99 O 7.98 ·10.02H 2 O. The structure was solved by direct methods and refined on the basis of 1797 independent reflections to  R  = 0.016. Belogubite is triclinic,  P 1 . Unit cell parameters are:  a  = 6.2548(1),  b  = 10.6112(2),  c  = 6.0439(1) A, α = 82.587(1), β = 109.625(1), γ = 104.848(1)°,  V  = 364.81(1) A 3 ,  Z  = 1. The strongest reflections of the powder XRD pattern are [ d obs , A ( I ) ( hkl )]: 5.73 (35) (100), 5.576 (47) (–110), 4.873 (100) (–111), 3.907 (31) (021), 3.719 (45) (0 –21), 3.229 (27) (111), 2.915 (25) (–221), 2.684 (26) (130). Belogubite is a new, CuZn-ordered member of the chalcanthite group having  M 1 cationic site preferentially occupied by Cu whereas  M 2 site is dominated by Zn with subordinate substitution of Fe 2+  and Mg. The mineral is named in honor of Elena Vitalievna Belogub (born 1963), major researcher of the Institute of Mineralogy of the Urals Branch of Russian Academy of Sciences, Miass, Chelyabinsk Oblast, Russia, a well-known expert in the mineralogy of volcanic-hosted massive sulfide copper deposits of South Urals.