Ultraviolet Telescopes
Sunday, August 7th, 2011
Fluorite Gemstones
Among mineral collectors, fluorite is the most popular mineral in the world next to quartz. Famed for its enormous range of colors, it is often referred to as the most colorful mineral in the world. But fluorite is not just another pretty stone; it has a number of fascinating properties and some very useful industrial applications.
Fluorite is interesting to mineral collectors because it has has several different crystal habits that produce well formed clean crystals. The cube is by far the most recognized habit followed by the octahedron. Fluorite has perfect octahedral cleavage. This means that it has four identical directions of cleavage and when cleaved in the right ways can produce a perfect octahedral or diamond shape. These cleaved octahedrons are very popular in rock and mineral shops.
Many fluorite specimens exhibit fluorescence under ultraviolet light. In fact the very term ‘fluorescence’ comes from the name ‘fluorite,’ not the other way round, since fluorite was one of the first fluorescent minerals studied. The visible light emitted by fluorite is usually blue, but red, purple, yellow, green and white also occur.
The origin of the name fluorite comes from the use of fluorite as a flux to lower the melting point in steel and aluminum processing. It was originally referred to as fluorospar by miners. Fluorite has many other industrial uses, such as a source of fluorine for hydrofluoric acid and fluorinated water.
Fluorite has been used instead of glass in some high performance telescopes and camera lens. Because fluorite has a very low dispersion,light diffraction is less than ordinary glass, and in telescopes it allows sharp imaging of astronomical objects even at high power.
Fluorite is of interest as a gemstone because of its remarkable range of colors and its attractive vitreous luster. Most specimens of fluorite have a single color, but many fluorites have multiple colors and the colors are arranged in bands or zones that correspond to the shapes of fluorite’s crystals. But it is quite a soft stone, rating only 4 on the Mohs scal. So it is not very practical for some types of jewelry such as rings, though it serves very well for pendants, earrings and brooches.
Purple or violet is the classic fluorite color, often rivaling amethyst for richness. Blue fluorite is fairly rare, and much sought after by collectors. The brilliant yellow is also quite rare. But the rarest fluorite colors are pink, black and colorless. Black fluorite is formed from exposure to radiation during the growth of the crystals. Colorless fluorite, though not especially attractive, is prized by collectors simply for its rarity.
About the Author
AJS Gems, Bangkok is a leading online dealer in fine gemstones, including fluorite, Burma ruby, sapphire, spinel, tourmaline and zircon. Color Change Fluorite
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