The origin of colour of chrysoprase from Szklary (Poland) and Sarykul Boldy (Kazakhstan)
Sachanbiński, Michał; Janeczek, Janusz; Platonov, Aleksej; Rietmeijer, Frans J.M.
published: Dec 14, 2001
Samples of chrysoprase from the chrysoprase ''type'' locality in Szklary, Poland and from Sarykul Boldy in Kazakhstan were investigated by analytical transmission electron microscopy, optical spectroscopy and infrared spectroscopy in order to determine the origin of its unique green colour. The allochromatic ''apple-green'' colour of chrysoprase results from nanometer-size inclusions of aggregates of Ni-bearing phyllosilicates and protophyllosilicates, mainly Ni-kerolite and minor pimelite, that occur predominantly draped on silica (sub-) grains. There is no evidence for bunsenite in the chrysoprases. The occurrence of mineral inclusions containing Fe3+ ions modify the chrysoprase green colour by adding yellowish hue. The bluish hues result from the λ-dependent light scattering on microdefects in the chalcedony matrix, e.g. silica globules, nano- and micrometer mineral inclusions and gas-liquid inclusions.