Colemanite

A major source of boron, colemanite was discovered in 1884 and named for the owner of the California mine where it was first found, William Tell Coleman. The color of this stone ranges from colorless to white to grey, sometimes yellowish. Specimens are very sensitive to heat. The short, prismatic crystals are often sought after by collectors. Colemanite is rarely seen in the form of gemstones as it presents a challenge to lapidaries because crystals are soft, brittle and have perfect cleavage.