I ritrovamenti sul suolo giapponese di ktenasite e ramsbeckite sono descritti in due articoli, relativamente recenti, di cui, qui di seguito, sono forniti gli abstract. Sono disponibili, per gli eventuali interessati, gli articoli nella loro interezza.
• Ohnishi, M., Kobayashi, S., Kusachi, I., Yamakawa, J., Shirakami, M. (2004): Ramsbeckite from the Hirao mine at Minoo, Osaka, Japan. Journal of Mineralogical and Petrological Sciences, 99, 19-24.
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 (Cu9.380Zn5.542Ni0.034Co0.027Fe0.020Mn0.013)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 2VX(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.
• Ohnishi, M., Kobayashi, S., Kusachi, I. (2002): Ktenasite from the Hirao mine at Minoo, Osaka, Japan. Journal of Mineralogical and Petrological Sciences, 97(Sueno Issue), 185-189.
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.
Marco E. Ciriotti
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