天然エメラルドの比重,屈折率および生成の深さ

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Specific gravity and refractive indices of emeralds from various types of deposits in the world were statistica:1ly examined. The following results were obtained. (1) Specific gravity increases with increasing mean refractive index, (2ω+ε)/3 following the correlation curve estimated from the Lorentz-Lorentz law. (2) The deviation from the curve is mainly caused by the amount of inclusions which are common in natural emeralds. (3) As for the refractive index, emeralds from the schist-type deposits and from some of the pegrnatite-type deposits are higher than any of synthetic emeralds in the market. Emeralds from the vein-type and the metasomatic-type deposits are comparable to hydrothermal synthetic emeralds and higher than flux-grown emeralds. (4) Emeralds with higher speciLic gravity and refractive indices occur in the schists and the gneissose pegmatites in the metamorphic regions where granitic and ultrabasic intrusives are found. (5) By using the results of high-pressure experiments and by assuming that the load pressure equals to the water pressure, the depth of fomation for emeralds can be estimated as follows : deeper than 60km for the schist-type emeralds from Pakistan, India, South Africa and Rhodesia ; shallower than 30km for the vein-type and thel metasomatic-type emeralds from Colombia and Brazil. Emeralds from Austria, Tanzania, Ura and Zambia were formed at 'the intermediate depth. These estimations seem to be reasonable, considering the mineral assemblage and the rock association in every deposit of emerald.
1977-12-15

天然エメラルドの比重,屈折率および生成の深さ

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