Fluorite
FLUORITE is not only a much-used industrial mineral, but is also highly sought after by collectors for its many colors, translucency, association with many other minerals, and cubic crystals. Chemically, fluorite is calcium fluorite, and is often found in hydrothermal vein deposits along with other minerals such as calcite, sphalerite, barite, galena and quartz. Large deposits of fluorite were mined in the Cave-in-Rock District of Illinois until the 1990's, and lesser amounts have been mined in many areas of the U.S., where it is often used as a flux in steel production. Other large deposits have been mined in Canada, England, China, and many other areas.
Fluorite is often found that fluoresces under ultraviolet light, most commonly blue, and the name "fluoresce" stems from the mineral name. Physically, fluorite is a soft mineral (H=4), and is easily identified by its colors, hardness, strong cubic cleavage and cubic crystals.
Fluorite is found in many colors, including purple, blue, green, yellow, pink, red, white, brown, and black. It is sometimes zoned, where outer layers have different colors and/or shades of colors. In the southern Illinois deposits, small chalcopyrite crystals were found within the fluorite crystals. Some of the massive Chinese deposits exhibit beautiful multicolored banding, and many carvings and beads have been made from this material.
Chemistry: Calcium fluoride (CaF2) ♦ Class: Halides ♦ Crystal system: Isometric ♦ Moh's hardness: 4 ♦ Transparency: Transparent to translucent ♦ Luster: Vitreous ♦ Color: Purple, blue, green or yellow; also colorless, reddish orange, pink, white, brown ♦ Cleavage: Perfect in 4 directions forming octahedrons ♦ Fracture: irregular and brittle ♦ Fluorescence: Blue or more rarely green, white, red or violet and may be thermoluminescent, phosphorescent and triboluminescent ♦ Localities: China, Germany, Austria, Switzerland, England, Norway, Mexico, and both Ontario and Newfoundland in Canada. It is found in many states in the US, notably Illinois.