Fluorite (#21)

A cluster of lustrous gem to gemmy purple to colorless banded and phantomed step growth cubes to 1 ½" across.
Africa Okarusu, Namibia 3" x 2 ½" x 1"

 

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We have seen fluorite earlier in this display, in specimens #3 and #7. We'll see it again in #28, #55, #65, and #66. Fluorite is a very common mineral, although it is not particularly abundant. It is not a major component of any type of rock, but it nonetheless occurs in many geologic environments, and some of the best display specimens are found in association with ore deposits. This specimen came from the Okorusu Fluorspar Mine in Namibia, on the southwest coast of Africa. Fluorspar is another name for fluorite, used more in the minerals industry than in scientific terminology. The purest fluorite mined is called acid grade fluorspar, and that is what is produced at the Okorusu Mine.

It is used to produce hydrofluoric acid, which can then be employed in the production of many fluorine-bearing chemicals used in industry.

Notice that the purple color in this specimen is very unevenly distributed. The purple color of fluorite occurs because of color centers - the absence of an F- ion in the crystal structure, replaced by an electron. This electron can be promoted to various unstable energy states by light, resulting in light of the requisite energies then being absent from the white light reflected by the mineral. (If "color center'' doesn't ring a bell for you, see the Learn More for specimen #9). Fluorite grows from fluids, and the composition of those fluids is not always constant. That means that the growth rate of the mineral also varies, and in turn, so does the abundance of defects in the crystal structure that lead to color centers. The fluorite then ends up being banded or containing "phantoms" in the interior of the crystals.