Colour, crystal chemistry, and mineral association of a green sphalerite from Steinperf, Dill syncline, FRG
Rager, Helmut; Amthauer, Georg; Bernroider, Manfred
European Journal of Mineralogy Volume 8 Number 5 (1996), p. 1191 - 1198
published: Oct 30, 1996
manuscript accepted: Apr 29, 1996
manuscript received: Oct 18, 1994
ArtNo. ESP147050805021, Price: 29.00 €
Abstract Green sphalerite and the coexisting minerals calcite and prehnite occur in small veins in a basalt from Steinperf, Dill Syncline, Germany. Chemical analysis by AAS and electron microprobe reveal that all three minerals are almost pure endmembers and contain only minor amounts of the transition elements. It is shown by optical absorption spectroscopy that small amounts of Co2+(80 ppm) in the tetrahedral Zn sites cause the green colour of this particular sphalerite. EPR studies of the specimen reveal that the cubic Zn positions are distorted by the incorporation of the Jahn Teller ion Co2+ without affecting the overall crystal structure. The minerals formed under hydrothermal conditions, starting with calcite and followed by prehnite, which crystallized under oxidizing conditions as indicated by the incorporation of Fe3+. Sphalerite formed under more reducing conditions as the last mineral in the sequence and incorporated all cobalt as Co2+.