Microstructure and origin of colour of chrysoprase from Haneti (Tanzania)

摘要

Chrysoprase from Haneti, Tanzania, was investigated by optical refl ectance spectroscopy, near infrared absorption spectroscopy and X-ray powder diffraction. Different to chrysoprase from other sources, the green colour is caused by the incorporation of 0.47(6) wt. % gaspeite in the microstructure of microcrystalline quartz. Like other varieties of chalcedony, the microstructure of chrysoprase is characterised by planar lattice faults, a small moganite content, small crystallite size of the quartz domains, microstrain associated with the structural imperfections and a small content of non-essential water. The crystallinity of chrysoprase from Haneti is higher than from many other sources.