|Chemical Composition||CaF2 – Calcium Fluoride|
|Color||Colorless or transparent when pure, but color may be extremely variable due to the presence of slight chemical impurities. The most common variety is violet, but fluorite may also be yellow, green, white, blue, gray, black or exhibit a variety of colors in zones or bands.|
|Cleavage||Perfect cleavage in four directions to produce octahedrons, brittle|
|Hardness||4 (relatively soft)|
|Specific Gravity||3.0-3.3 (average ‘weight’)|
|Luster||Crystals are vitreous (glass-like)|
Fluorite commonly forms transparent to translucent crystals that can initially be mistaken for a variety of other minerals. Misidentifications may also arise due to the wide range of colors that fluorite can exhibit. However, fluorite’s intermediate hardness, perfect cleavage in four directions, and common fluorescence should allow it to be easily distinguished from other minerals that share a similar appearance.
At first glance, fluorite crystals may be mistaken for quartz crystals, especially the purple variety of quartz known as amethyst. However, quartz is much harder than fluorite. It will scratch glass and, unlike fluorite, it cannot be easily scratched by metal. Quartz also lacks any cleavage and breaks in a conchoidal manner, while fluorite has four perfect cleavage directions. In addition, fluorite will often fluoresce under ultraviolet light.
Halite is another halide mineral that also shares a similar crystal form with fluorite. The two can be distinguished, however, by their different cleavages, their taste, and their different hardness. Fluorite cleaves in four directions to form octahedrons, while halite has perfect cleavage in three directions to form cubes, so the cleavage planes of halite always form at right angles to one another. Halite has a distinctive salty taste and is softer than fluorite, being easily scratched by a fingernail. With a hardness of 4, fluorite is more resistant to being scratched, although it is still much softer than glass or metal.
Calcite and fluorite can be distinguished by differences in cleavage. Fluorite cleaves in four directions to form octahedrons, while calcite cleaves in three directions to form rhombohedra. The two share a similar hardness, but calcite will readily bubble, or effervesce, in dilute acid, while fluorite does not react to dilute acid.
Did you know...
Many people mistakenly assume that the mineral fluorite got its name from the element fluorine, but the reverse is true. The element fluorine actually derives its name from fluorite and is a deadly poison that killed or permanently injured a number of scientists involved in its original isolation and identification.
From improved dental health via fluoridated water and toothpaste to the development of nuclear energy and atomic bombs, fluorite’s legacy spans the spectrum of fluorine use in our society across medical, chemical and industrial fields. Although fluorine occurs in a variety of minerals, fluorite is our main source of fluorine simply because of its abundance and high fluorine content.
Description and Identifying Characteristics
Although fluorite is not particularly abundant, it is one of the more familiar minerals because it forms well-developed crystals in a variety of colors that are widely collected and traded. These crystals are transparent to translucent and form distinctive cubic or octahedral crystals (similar in shape to 6-sided and 8-sided dice). Fluorite that forms from higher temperature fluids tends to occur as octahedral crystals, while fluorite that forms from lower temperature fluids tends to occur as cubic crystals. Pure fluorite crystals are clear, so the many colors fluorite crystals come in simply reflect a variety of minor impurities in the crystal’s chemical composition that tint the crystal. Some fluorite crystals display bands of color in complex patterns that record subtle changes in the chemistry of the fluids from which the crystal formed. Although fluorite crystals occur in a range of colors, dark purple fluorite crystals are probably the best-known 