Abstract
Ktenasite was found as a vein forming mineral in the altered shale of Tamba zone of Jurassic age, at the Hirao mine, Minoo, Osaka, Japan. The mineral was also found in a marginal part of sphalerite in the host rock. This is the first occurrence of ktenasite in Japan. Ktenasite occurred as aggregates of flattened prismatic crystals up to 0.5 mm long and 0.1 mm wide, in association with minerals such as chalcopyrite, serpierite, smithsonite, hydrozincite, and limonite. An EPMA and CHNS/O analyzer gave the empirical formula (Cu3.446Zn1.451Co0.080Pb0.018Ni0.007)Σ5.002(SO4)2.003(OH)5.998·5.99H2O on the basis of O = 20. The unit cell parameters were a = 5.590(1), b = 6.161(1), c = 23.741(3) Å, and β = 95.628(3)°. The Vickers microhardness was 113 kg/mm2 and Moh's hardness was 2.5. The density was 2.93 g/cm3. It is likely that ktenasite at Minoo was formed by a reaction of the Cu-bearing fluids with sphalerite.
