Uvarovite garnet from the Ural Mountains, Russia. (more below)
Photo courtesy fluor_doublet of flickr.com under Creative Commons license
Uvarovite is one of the calcium garnets of the "ugrandite" group, along with grossular and andradite. Its composition is Ca3Cr2(SiO4)3, and it has a brilliant emerald-green color from the chromium ion.