Fluorite

The reference mineral for hardness 4 on the Mohs scale, fluorite is a calcium fluoride (CaF2) celebrated for its wide spectrum of colors, whether purple, blue, green, yellow, pink, or colorless. It crystallizes in the cubic system, most often as cubes or octahedra, with a vitreous luster, a white streak, and perfect octahedral cleavage. Its specific gravity ranges from 3.13 to 3.18. Many specimens glow strongly under ultraviolet light, and the phenomenon of fluorescence was in fact named after this mineral. Fluorite serves as a flux in metallurgy and as a source of fluorine compounds. A specific gravity near 3.15 and only moderate hardness set it apart from the harder, denser minerals it accompanies in veins.

フッ化カルシウムで、紫色、黄色、緑色が一般的である。光学用ガラスと製鋼用フラックスに使用される。