Fluorite

Fluorite, or fluorspar, chemical name Calcium fluoride (CaF2) is a mineral
often found in the "tailings" or discarded debris from other mineral
extraction processes. Some other common tailings are: Arsenic, Barite,
Calcite, Cyanide, Mercury, Pyrite, Quartz. Deposits are mainly found in
igneous rock and to a lesser extent in Dolomite and Limestone. Deposits
can also be found commonly in hydrothermal veins where it is often the
only mineral occuring.

Although Fluorite is most commonly blue (e.g. that found at the Blue John
mine, Derbyshire, England), other colours such as red, purple, yellow,
green & white can also occur, depending on the location of the find. The
classic Blue John from Derbyshire is now quite rare and limited amounts
are now mined, mainly for ornamental purposes and to supply the
gemstone trade. No wonder it is known as the most beautifully coloured
mineral!

Uses of Fluorspar.
Its main uses are in the manufacture of opalescent glass, hydrofluoric
acid (useful for glass etching), and also for making superior optics for
telescopes and lenses due to its low diffraction properties. Other uses
include enamel making, and as a flux in steel making.
It has been used since Roman times for making beautiful ornamental
vases and drinking vessels, some excellent examples of which can be
seen at the Blue John mines, Derbyshire.

Fluorspar Properties.
A notable property of fluorite is its ability to fluoresce in the presence of
ultra-violet light, showing off its myriad of colours to good effect. Some
types of fluorite also exhibit thermoluminescence whereby they will glow
in the dark when subjected to heat, even as low as body heat with some
specimens. This is essentially a 'one-off' property as a sample will not
repeat this effect again if reheated.

Galena