Rainbow Pyrite Concretion - Russia

A spire of sparkle and color in this "Rainbow" Pyrite specimen from Ulyanovsk, Ulyanovsk Oblast, Russia. The rainbow colors are completely natural, and are a result of oxidization of the pyrite, sometimes referred to as Rainbow Pyrite. They form inside hard concretions found along river beds in Russia. The gray and earth-tone exterior looks like an ordinary rounded rock when first unearthed. The concretions must then be cracked open (similar to a geode) to expose the glittery crystals inside. When tilted in the light, the glittering Pyrite appears to change colors slightly when exposed to different lighting conditions!