Emerald

The vivid green variety of beryl, emerald ranks among the Big Four precious gemstones alongside diamond, ruby, and sapphire, and has been treasured above almost all other green stones for more than four thousand years. Chromium and vanadium supply its color, and fine emeralds can command higher per-carat prices than D-flawless diamonds, with the most prized material from Colombia's Muzo, Coscuez, and Chivor mines. It crystallizes in the hexagonal system at 7.5 to 8.0 on the Mohs scale, though internal fractures make it more delicate than that figure suggests; its characteristic inclusions, called jardin, are accepted as fingerprints of natural origin. Further material comes from Zambia's Kagem mine, Brazil's Minas Gerais, and Afghanistan's Jegdalek. An investment-tier precious stone, emerald is the birthstone for May.