Fluorite
Fluorite (also called fluorspar) is the mineral form of calcium fluoride, CaF2. It belongs to the halide minerals. It crystallizes in isometric cubic habit, although octahedral and more complex isometric forms are not uncommon.
| Fluorite | |
|---|---|
Deep green isolated fluorite crystal resembling a truncated octahedron, set upon a micaceous matrix, from Erongo Mountain, Erongo Region, Namibia (overall size: 50 mm × 27 mm, crystal size: 19 mm wide, 30 g) | |
| General | |
| Category | Halide mineral |
| Formula (repeating unit) | CaF2 |
| IMA symbol | Flr |
| Strunz classification | 3.AB.25 |
| Crystal system | Isometric |
| Crystal class | Hexoctahedral (m3m) H–M symbol: (4/m 3 2/m) (cF12) |
| Space group | Fm3m (No. 225) |
| Unit cell | a = 5.4626 Å; Z = 4 |
| Identification | |
| Color | Colorless, although samples are often deeply colored owing to impurities; Purple, lilac, golden-yellow, green, blue, pink, champagne, brown. |
| Crystal habit | Well-formed coarse sized crystals; also nodular, botryoidal, rarely columnar or fibrous; granular, massive |
| Twinning | Common on {111}, interpenetrant, flattened |
| Cleavage | Octahedral, perfect on {111}, parting on {011} |
| Fracture | Subconchoidal to uneven |
| Tenacity | Brittle |
| Mohs scale hardness | 4 (defining mineral) |
| Luster | Vitreous |
| Streak | White |
| Diaphaneity | Transparent to translucent |
| Specific gravity | 3.175–3.184; to 3.56 if high in rare-earth elements |
| Optical properties | Isotropic; weak anomalous anisotropism; moderate relief |
| Refractive index | 1.433–1.448 |
| Fusibility | 3 |
| Solubility | slightly water soluble and in hot hydrochloric acid |
| Other characteristics | May be fluorescent, phosphorescent, thermoluminescent, and/or triboluminescent |
| References | |
The Mohs scale of mineral hardness, based on scratch hardness comparison, defines value 4 as fluorite.
Pure fluorite is colourless and transparent, both in visible and ultraviolet light, but impurities usually make it a colorful mineral and the stone has ornamental and lapidary uses. Industrially, fluorite is used as a flux for smelting, and in the production of certain glasses and enamels. The purest grades of fluorite are a source of fluoride for hydrofluoric acid manufacture, which is the intermediate source of most fluorine-containing fine chemicals. Optically clear transparent fluorite lenses have low dispersion, so lenses made from it exhibit less chromatic aberration, making them valuable in microscopes and telescopes. Fluorite optics are also usable in the far-ultraviolet and mid-infrared ranges, where conventional glasses are too opaque for use.