Fluorite

Fluorite (also called fluor-spar or Blue John) is a mineral composed of calcium fluoride, CaF₂. It is an isometric mineral with a cubic habit, though octohedrons and dodecahedrons are not uncommon.

Table of contents

1 Occurrence

1.1 Blue John

2 Uses
3 Details

Occurrence

Pig carved in fluorite,
5 cm (2 inches) long.

Octahedral fluorite crystals.

Fluorite may occur as a vein deposit, especially with metallic minerals, where it often forms a part of the gangue (the worthless `host-rock' in which valuable minerals occur) and may be associated with barite, quartz and calcite. It is a common mineral in deposits of pneumatolytic origin and has been noted as a primary mineral in granites and other igneous rocks.

Blue John

One of the most famous of the older localities of fluorite is Derbyshire, England, where under the name of Derbyshire Blue John beautiful blue fluorite is used for ornamental purposes; its softness, however, has been a bar to general use.

Uses

As well as ornamental uses, fluorite is also used as a flux in the manufacture of steel, in the making of opalescent glass, enamels for cooking utensils, and for hydrofluoric acid. The name fluorite is derived from the Latin fluo, flow, in reference to its use as a flux.

Details

Crystallographic system	Cubic
Colours	White or colorless, blue, blue-green, yellow, brownish-yellow, or red.^*
Lustre	Vitreous
Hardness	4
Refractive index	1.433-1.435
Specific gravity	3.18
Cleavage	1 (octahedral)
Pleochroism	None

^*Note on colours: The blue kind is often a delicate violet-blue, sometimes amethystine in tint. Certain specimens appear blue by reflected light and green or yellow by transmitted light. Fluorite sometimes phosphoresces when heated or scratched. Other varieties fluoresce beautifully under the influence of X-rays or ultraviolet light.