Kapellasite, Cu (sub 3) Zn(OH) (sub 6) Cl (sub 2) , a new mineral from Lavrion, Greece, and its crystal structure

Kapellasite, Cu (sub 3) Zn(OH) (sub 6) Cl (sub 2) , is a new secondary mineral from the Sounion No. 19 mine, Kamariza, Lavrion, Greece. It is a polymorph of herbertsmithite. Kapellasite forms crusts and small aggregates up to 0.5 mm, composed of bladed or needle-like indistinct crystals up to 0.2 mm long. The colour is green-blue, the streak is light green-blue. There is a good cleavage parallel to {0001}. Kapellasite is uniaxial negative, omega = 1.80(1), epsilon = 1.76(1); pleochroism is distinct, with E = pale green, O = green-blue. D (sub meas) = 3.55(10) g/cm (super 3) ; D (sub calc.) = 3.62 g/cm (super 3) . Electron microprobe analyses of the type material gave CuO 58.86, ZnO 13.92, NiO 0.03, CoO 0.03, Fe (sub 2) O (sub 3) 0.04, Cl 16.70, H (sub 2) O (calc.) 12.22, total 101.80, less O = Cl 3.77, total 98.03 wt.%. The empirical formula is (Cu (sub 3.24) Zn (sub 0.75) ) (sub Sigma 3.99) (OH) (sub 5.94) Cl (sub 2.06) , based on 8 anions. The five strongest XRD lines are [d in Aa (I/I (sub 0) , hkl)] 5.730 (100, 001), 2.865 (11, 002), 2.730 (4, 200), 2.464 (9, 021/201), 1.976 (5, 022/202). Kapellasite is trigonal, space group P3m1, unit-cell parameters (from single-crystal data) a = 6.300(1), c = 5.733(1) Aa, V = 197.06(6) Aa (super 3) , Z = 1. The crystal structure of kapellasite is based on brucite-like sheets parallel to (0001), built from edge-sharing distorted M(OH,Cl) (sub 6) (M = Cu, Zn) octahedra. The sheets stack directly on each other (...AAA... stacking). Bonding between adjacent sheets is only due to weak hydrogen and O...Cl bonds. The name is in honour of Christo Kapellas (1938-2004), collector and mineral dealer from Kamariza, Lavrion, Greece.