Mineral chemistry of schulenbergite and its Zn-dominant analogue from the Hirao mine, Osaka, Japan

Abstract

Schulenbergite and its Zn-dominant analogue occur in the Hirao mine, Osaka Prefecture, Japan. The minerals were found as crusts on the same gallery wall and in cracks of altered shale. The minerals occur as aggregates of hexagonal platy crystals up to 0.5 mm across and 0.05 mm thick. The schulenbergite is greenish blue to blue-green in color, and the Cu/(Cu + Zn) molar ratio varies from 0.67 to 0.42. The Zn-dominant analogue of schulenbergite is pale blue in color, and the Cu/(Cu + Zn) molar ratio varies from 0.30 to 0.21. The average unit cell parameters of schulenbergite and its Zn-dominant analogue calculated from the X-ray powder diffraction data were: a = 8.256 (2) and c = 7.207 (3) Å, and a = 8.292 (2) and c = 7.271 (4) Å, respectively. It is likely that schulenbergite and its Zn-dominant analogue from the Hirao mine were formed as secondary minerals from Cu and Zn ion-bearing solution that were derived from chalcopyrite and sphalerite in the host rock.