Fluorite from Tammy's Jewelry and Gem Box Gemological Information


The beautiful cubic crystals of fluorite, so many fine specimens of which grace our museums, are occasionally cut as gemstones, usually in the trapcut style and mainly for collectors, for the hardness of fluorite (fluorite is the standard 4 on Mohs's scale) is far too low to resist the wear and tear encountered in jewellery. The range of colour shown by fluorite is equalled by few other gemstones. The crystals may be colourless, yellow, brown, green, blue, violet and pink, but a true red is not known. An emerald-green fluorite probably from near Otjiwaron-go, in Namibia, has been faceted and sold under the misnomer 'South African emerald'.


Apart from the localities already mentioned fluorite is found, often in lovely crystal groups, at Weardale in Durham, Alston and Cleator Moor in Cumberland, in the lead mines of Derbyshire and in Cornwall, indeed it may be said that England provides the finest fluorite crystals. The Swiss source at Chamounix is notable for the pink octahedral crystals and fluorite is also found at Brienz, Berne. The mineral is obtained from many localities in the United States of America, the more important being in the States of Illinois, New Hampshire and Missouri. There are other sources in Ontario, Canada, in Saxony, Bavaria and Baden in Germany, in Bohemia, Czechoslovakia and in Silesia, Poland. Italy and Norway also supply fluorite.

Chemical and Physical Properties

Fluorite is calcium fluoride (CaF2) and crystallises in the cubic system, most commonly as cubes and rarely as octahedra and dodecahedra. The cube forms are often bevelled at the edges by a form of a lower crystallographic index, and the cube faces often show very low pyramids (vicinal faces), which produce striations on the surface. Inter-penetrant twinning is common and, due to parallel grouping of minute cubes, some crystals, particularly those of octahedral habit, exhibit faces with a drusy character. Many fluorite crystals are coated with quartz or pyrites crystals, and some apparent fluorspar crystals are quartz or chalcedony pseudomorphs after fluorite.

Fluorite has an easy octahedral cleavage, but the highly characteristic cleavage surfaces are rarely perfect showing a stepped effect; it is this easy cleavage which makes the cutting of the crystals so difficult. The fracture, which is overshadowed by the easy cleavage, is flat conchoidal but in the compact types may be splintery. The density of fluorite is 3.18 and does not vary much from this figure in the case of crystals, but the massive types, owing to contamination with impurities, may vary between 3.00 and 3.25. The refractive index is 1.434 and the dispersion is very small (0.007 B to G). The absorption spectrum is generally vague and indecisive, but in the green variety weak bands occur at 6340, 6100, 5820 and 4450 A, and there is also a strong broad band at 4270 A which may be seen in sizeable pieces.

from "Gems, Their Sources, Descriptions and Identification," by Robert Webster and BW Anderson, 1962. Copyright © 1983.


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