When found in nature, fluorspar is known by the mineral name fluorite. Fluorspar (fluorite) is calcium fluoride (CaF₂). It is found in a variety of geologic environments. Fluorspar is found in granite (igneous rock), it fills cracks and holes in sandstone, and it is found in large deposits in limestone (sedimentary rock). The term fluorspar, when used as a commodity name, also refers to calcium fluoride formed as a by-product of industrial processes.

Fluorspar is relatively soft, number 4 on Mohs' scale of hardness. Pure fluorspar is colorless, but a variety of impurities give fluorite a rainbow of different colors, including green, purple, blue, yellow, pink, brown, and black. It has a pronounced cleavage, which means it breaks on flat planes. Fluorite crystals can be well formed, beautiful and highly prized by collectors.

Despite its beauty and physical properties, fluorspar is primarily valuable for its fluorine content.

Even though fluorite contains the element fluorine, its name is not derived from its chemical composition. The name was given by Georg Agricola in 1546 and was derived from the Latin verb fluere which means to flow because it melts easily.

Spar is a generic name used by mineralogists to refer to any non-metallic mineral that breaks easily to produce flat surfaces and which has a glassy luster.

A miner’s name used long ago for fluorite was Blue John.

The United States once produced large quantities of mineral fluorspar. However, the great fluorspar mines of the Illinois-Kentucky fluorite district are now closed. Today, the United States imports fluorspar from China, South Africa, Mexico, and other countries.

A small percentage of the fluorspar consumed in the United States is derived as a by-product of industrial processes. For instance, an estimated 5,000 to 8,000 tons of synthetic fluorspar is produced each year in the uranium enrichment process, the refining of petroleum, and in treating stainless steel. Hydrofluoric acid (HF) and other fluorides are recovered during the production of aluminum.

The remainder of fluorspar consumption is as a flux in making steel, glass, enamel, and other products. A flux is a substance that lowers the melting temperature of a material.

Phosphoric acid plants, which process phosphate rock into phosphoric acid, produce a by-product chemical called fluorosilicic acid. This is used to fluoridate public water supplies or to produce AlF3. Phosphate-rich rocks are a minor alternative source for elemental fluorine.

Yellow fluorite from Illinois	Pink fluorite from Peru
Green fluorite from Colorado	Fluorite crystal drawings by Darryl Powell Ó 1999 Darryl Powell Used with permission.