Calcium Fluoride (CaF2)
Fluorite, or calcium fluoride (CaF2), is a simple halide commonly occurring as a glassy, hued, vein in a variety of mineral environments. It is commonly found in metallic hydrothermal deposits associated with lead, silver, galena, sphalerite, cobalt and other economic minerals. It also occurs in cavities of pegmatites, in hot-springs areas and in sedimentary rocks, primarily limestones that have been permeated by aqueous fluoride.
One of fluorite's ingredients, the active element fluorine, is a violent poison that is also the most active of elements, capable of eating through glass and metal. Discovery and isolation of this element caused the death and permanent injury of many scientists. Another fluorine compound, hydrofluoric acid, is used to etch glass, dissolve quartz, and other minerals.
But fluorite is a harmless mineral of great beauty and variety, ranging from yellow to green, and from to blue to red and all of the shades in between. It forms in lovely crystals that range from simple cubes to complex combinations showing as many as 48 faces or more.
Though much too soft to be a jewelry mineral, hardness 4.0 on the Moh's scale, it is extensively used in carvings, in interior decorating and inexpensive art objects. Sold commercially as fluorspar, it is usually quite pure, but as much as 20 percent yttrium or cerium may replace calcium. It is one of the most popular minerals among collectors because it is a common mineral that can be obtained in a full range of prices.
The vast deposits of fluorite in the Illinois-Kentucky area are largely depleted now, but mineral collections are still rich in their specimens. Some of the world’s most prized fluorite specimens come from Swiss and French Alp deposits where the crystals occur as simple octahedrons and range in color from a delicate pink to a rich red.
Fluorite is found worldwide in China, South Africa, Mongolia, France, Russia, and the central North America. Here, noteworthy deposits occur in Mexico, Illinois, Missouri, Kentucky and Colorado in the United States.
Fluorite is used in opalescent glass, and at one time, Blue John, a variety from Derbyshire, England, was widely used in ornamental vases and other objects. It is used as a flux in metallurgical processes, like open-hearth steel and steel enamelware, in the production of hydrofluoric acid, in the refining of lead and antimony, and in the manufacture of high-octane fuels.
Because of its low index of refraction and low dispersion, the rare, clear crystals of the mineral are valuable in making lenses and prisms for optical systems using ultraviolet light. Cryolite is a fluoride of aluminum and sodium.
4.0 (Mohs' scale)
- Color: Colorless, black, white brown, and all pastels in between
-- Bob Katz
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