Fluorite represents one of the widest colour ranges of any natural mineral and the colours are often bright and vibrant. With that said, the application of heat or exposure to bright light may cause colours to fade so it's advisable to keep fluorite out of direct sunlight. Although hues of yellow, green, blue and purple are the most common, it can also be white, blue, red or brown. In its purest form fluorite is colourless and either transparent or translucent with a glassy lustre. When void of impurities it consists of 51.1% calcium and 48.9% fluorine but the presence impurities introduces small amounts of silicon, aluminium and magnesium. It can also feature inclusions of gasses and fluids such as petroleum and water. The impurities in the crystal cause the change in colour but radiation can also be a contributing factor. Crystals tend to be well formed and are widely found as cubes. Fluorite can also be occur in massive form which means instead of featuring individual crystals, the crystals are intergrown hence the crystal structure of the mineral is not visible.
Although fluorite can be found in a wide range of geological environments in many places around the world, only a handful of localities have produced large quantities of fine grade gemstones. England has produced some of the finest specimens in areas such as Durham, Cornwall and Cumberland. Castleton in Derbyshire is famous for a rare type of fluorite known as Derbyshire Blue John. The stone which can be found nowhere else in the world occurs in massive form and exhibits bands of yellow and purple colour. It's now almost completely mined out hence is extremely rare.
The name fluorite originates from the Latin word 'fluere' meaning 'to flow' because it has a very low melting point. This name is a reference to the ease in which it melts when being used as a flux in the smelting and refining of metals. Fluorite is widely used in industry where it's referred to as fluorspar. It's used in the manufacture of fibreglass, ceramics and opaque glass and is also used in the chemical and iron and steel industries. The mineral form of calcium fluoride, it's the main source of natural fluorine which is used for the fluoridation of water, in toothpaste because of its ability to fight cavities and in Teflon where it helps provide the non stick surface of cooking pans.
Fluorite is known to have been used in Ancient Egypt and was also mined by the Romans, two fluorite cups which date from around 50 - 100 AD are currently housed in the British museum.
One of the more famous minerals that fluoresces in a great variation of colour when exposed to ultraviolet (UV) light, the word 'fluorescent' comes from 'fluorite' because it was the first mineral in which this phenomenon was observed. The fluorescence is caused because of certain impurities within the crystal structure. Interestingly not all fluorite will fluoresce even if obtained from the same locality.
In crystal healing fluorite with violet or purple colour is said to aid meditation, when hints of light blue are present it helps with patience, contentment and happiness. Dark blue colouration is said to attract a change in circumstances and psychic ability and green has a positive influence over matters of employment, money, growth and fertility. Yellow fluorite is known for strengthening intellect and study stamina and orange is often linked with energy, stimulation and stamina (both physical and spiritual) as well as the ability to cope in times of crisis. Fluorite carries an energy that can bring calm to chaos and helps to restore a balance within the four levels that make us human, the mental, emotional, physical and spiritual. Stones are often recommend to be placed around computers and the workplace in order to reduce electromagnetic stress and relieve negative forces.
Fluorite is popular with mineral collectors and for use in items of jewellery but it's a soft and fragile stone that fractures easily. On Mohs scale of mineral hardness it grades just 4 so must be handled carefully.
Notable deposits occur in Germany, Austria, Switzerland, England, Norway, Mexico and Canada. Illinois has historically been the largest producer in the United States however the last mine closed in 1995. The Illinois general assembly passed a resolution in 1965 declaring fluorite as its official state mineral.
Wikipedia on fluorite
More facts on fluorite
Fluorite aka fluorspar by Geology.com