Ramsbeckite from the Hirao mine at Minoo, Osaka, Japan

Ramsbeckite was found as a vein forming mineral in altered shale at the Hirao mine, Minoo, Osaka, Japan. It occurred as aggregates of euhedral granular crystals up to 0.5 mm across, in association with sphalerite, chalcopyrite, smithsonite, aurichalcite, amorphous manganese dioxide, schulenbergite, brochantite, serpierite, limonite and an unidentified mineral. It was emerald green to blue-green in color with a vitreous luster in hand specimen. An EPMA and CHNS/O analyzer gave the empirical formula (Cu_9.380Zn_5.542Ni_0.034Co_0.027 Fe_0.020Mn_0.013)_σ15.016[(SO₄ )_3.871(CO₃)0.166]_σ4.037(OH) _21.958 6.06H₂O on the basis of O = 44. The unit cell parameters were a = 16.106 (3), b = 15.568 (2), c = 7.109 (1) Å, β = 90.23 (1)°, and Z = 2. The mineral was optically biaxial negative with refractive indices α = 1.676, β = 1.704 and γ = 1.707, and 2V_X(calc) = 37.8°. The Vickers microhardness was 162 (144-182) kg/mm² (10 g load), and the Mohs hardness was 3.5. The measured density was 3.36 g/cm³. It is likely that ramsbeckite at the Hirao mine crystallized from Cu and Zn-bearing fluids.