FLUORITE INFORMATION

Quick	Facts
Group:	Halides
Crystal system:	Cubic
Chemical formula:	CaF2
Hardness:	4
Density:	3.18
Cleavage:	Perfect
Fracture:	Conchoidal
Colour:	Colourless (allochromatic)
Streak:	White
Lustre:	Vitreous
Fluorescence:	Pink or violet

Fluorite, sometimes still known by its old name, fluorspar, is variable in colour.  It is most often blue, green, purple or yellow, but can sometimes be black, pink, red or altogether colourless.  In addition, individual specimens may be banded or "colour-zoned".  The name comes from the Latin fluere, meaning "to flow": this is principally a reference to the mineral's low melting point.  Fluorite has a wide range of industrial applications - it is used to make opalescent glass and is a component of iron and steel enamelware; it is also a flux in the manufacture of some forms of steel.  Most importantly, fluorite is the main source of fluorine gas and hydrofluoric acid.  Fine specimens of blue fluorite, known as blue john, came from Derbyshire, England, and were widely used in the 19th century to make stunning vases.

Fluorite is a member of the halide group of minerals.  Each molecule of the mineral is made up of one atom of metallic calcium joined to two atoms of fluorine.  The basic structure of fluorite crystals is cubic, too, although eight-sided and 12-sided shapes may also be found.  Crystals often run into each other in the phenomenon known as twinning.  Fluorite is a fairly soft mineral, scoring only 4 on the Mohs Scale of hardness - it can e easily scratched with the blade of an ordinary knife.  It is extremely sensitive to heat and melts (fuses) easily in an open flame.  Fluorite is usually fluorescent, showing pink or violet under an ultra-violet light.  However, the strength of this effect can vary enormously from specimen to specimen.

Although Fluorite is primarily an industrial mineral, some crystals are gem-quality.  However, even the finest samples have limited use because they are not hard enough to withstand the wear and tear of everyday use.  Yet, although most fluorite is fashioned for display in mineralogists' collections, some pieces are used in jewellery.  These are typically cut in cabachons and then capped with a protective outer layer of a form of quartz called rock crystal.  In addition to being more resilient than fluorite, rock crystal is translucent and consequently the colours of the fluorite can easily be seen through it.  Fluorite is also used to make carvings and brooches with carved designs called intaglios.  When fluorite is faceted, the usual cutting angles are 40-50 degrees along the crown surfaces and 43 degrees on the pavilions.  Fluorite is usually quite pure, but in some specimens as much as 20% of the calcium in the mineral may be replaced by metallic yttrium.  This variant form is usually violet, grey or reddish brown in colour and is known as yttrian fluorite.  Less frequently, some of the calcium in fluorite may be replaced by another metallic element, cerium.

As its name implies, fluorite may show a strong fluorescence under ultra-violet light.  Specimens are often covered with layers of calcite.  These can be removed with dilute hydrochloric acid.  Iron stains are also common and can be removed by wiping the surface with oxalic acid.  Importantly, all acids should be treated with great care and never used without adult supervision.  No attempt should be made to clean specimens of yttrian fluorite.

Fluorite is a widespread mineral found in a large number of mineral veins which have been altered by hot water (hydrothermals) and around hot springs.  It may form on its won or in association with various metallic ores, especially those of lead and silver.  In deposits of the latter type it tends to form in small quantities and is known as a gangue mineral.  Among the many minerals with which fluorite may be associated in this way are barite, calcite, cassiterite, celestine, dolomite, galena, quartz, sphalerite and topaz. 

The following are some of the main locations in which substantial deposits of fluorite have been found:  Freiberg (Germany); Bolzano, Lazio and Tuscany (Italy); and St Gotthard (Switzerland).  In the United States, fluorite is found at Crystal Peak, Colorado, and in Harden County,  Illinois.  Yttrian fluorite is found in Sussex County, New York State; the other main source of this form of the mineral is Falun (Sweden).  Fluorite is reasonably common all over the British Isles, and is principally mined in the following places: Cleator Moor, Cumbria; Derbyshire; Devon; Weardale, Durham and the lead veins of Northumberland.  The beautiful blue john can still be found, but the main veins are now worked out and it is no longer mined on an industrial scale.