“Cuboids” of pyrope found in Siberian Platform

Abstract

Pseudocubical convex-faceted grains of pyrope are often found in upper parts of weathered crust, in sedimentary rocks and in modern alluvium, inside and outside the Yakutian diamond fields. They are never in the diamond pipes or in dense kimberlites where pyrope maintains its normal shape. The “cuboid” shape of pyrope grains is probably due to diagenetic and solubility effects, inasmuch as their optical properties and impurities are the same as those of the “normal” pyrope.