ite 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 fluorite variety as they are often prominently displayed in museum galleries and mineral book photos. These dark purple or violet crystals are easily confused with amethyst (purple quartz), although fluorite’s distinctive crystal shape, four planes of cleavage, and its relative softness can distinguish the two.
Fluorite exhibits perfect cleavage in four directions to form octahedrons. It is most often found as a pore-filling void or vein deposit, so the fluorite crystals tend to occur as a distinct layer or series of layers lining the walls of what was originally a void in the rock.
One of fluorite’s more unusual properties is that it will fluoresce, or glow, under ultraviolet light. It was one of the first materials in which the phenomena of fluorescence was recognized and studied, and the term ‘fluorescence’ actually comes from the mineral name ‘fluorite’.
In Our Earth: The Geologic Importance of Fluorite
Fluorite primarily occurs as a pore-filling mineral in carbonate rocks (limestones and dolostones), as low temperature hydrothermal vein deposits associated with lead and silver ores, and less often as an accessory mineral in pegmatites and granites. It is sometimes even precipitated at hot springs.
Limestone and dolostone rocks through which low temperature hydrothermal fluids have moved may be particularly rich in fluorite. In the past, carbonate rocks of the Mississippi River Valley hosted some of the world’s richest fluorite deposits, but most of these have since been mined away. When fluorite occurs as a cavity fill in carbonate rocks it is usually associated with calcite, dolomite, anhydrite, gypsum and sulfur. In hydrothermal vein deposits, fluorite may be found with calcite, dolomite, barite, galena, sphalerite, and even silver ores.
In Our Society: The Economic Importance of Fluorite
The name ‘fluorite’ comes from the Latin word ‘fluere’ that means “to flow.” Fluorite melts easily and is used as a flux in the smelting of metallic ores. A ‘flux’ is a material used to help remove impurities from ore as 