A study of isotropic-pseudoanisotropic zoning in sphalerite

Sphalerite with isotropic-pseudoanisotropic zoning is described from greisen in Eurajoki, SW Finland. Singlecrystal X-ray studies showed that the pseudoanisotropy is due to very small chalcopyrite inclusions, oriented with their crystallographic axes parallel to the sphalerite axes. Electron probe microanalyses are presented for the isotropic central part and for the pseudoanisotropic marginal zone of a sphalerite crystal. The main chemical difference between the zones is that the FeS content (19.2 mole per cent) of the central part is essentially replaced by CuFeSa (12.1 mole per cent) in the marginal zone. The zonal structure is interpreted to be of secondary origin.