Fluorite cubes octahedral

Fluorite is a mineral composed of calcium fluoride (CaF₂), known for its cubic and octahedral crystals and wide range of colors.

About this subject

Fluorite, also known as fluorspar, is a halide mineral composed of calcium fluoride (CaF₂). It crystallizes in the cubic system, frequently forming perfect cubes, octahedra, or combinations of both (cuboctahedra). It can also occur as dodecahedra. Its hardness is 4 on the Mohs scale, making it relatively soft and easily cleavable into octahedra.

A striking property is fluorescence: many specimens glow under ultraviolet light due to impurities such as yttrium or rare earth elements. The name fluorite derives from Latin "fluere" (to flow), referencing its use as a flux in metallurgy. Colors range from purple, green, blue, yellow, colorless to pink and black, depending on crystal lattice defects or inclusions.

Economically, fluorite is the primary source of fluorine, used in the production of hydrofluoric acid and in the aluminum industry. It is also employed as a flux in steelmaking and in manufacturing high-quality optical lenses and windows, as it transmits ultraviolet and infrared light. Notable deposits include the Rogerley mines (England), Illinois (USA), Hunan (China), and Asturias (Spain).

Fluorite crystals can grow in cavities of sedimentary rocks, hydrothermal veins, or pegmatites. The combination of cubes and octahedra is common when crystallization occurs under moderate supersaturation. Collectors value specimens with intense colors and well-defined forms, especially rare blue or green octahedra.

Frequently Asked Questions

Is fluorite always fluorescent?

No. Not all fluorite is fluorescent. Fluorescence occurs when impurities like europium or yttrium substitute for calcium in the crystal lattice. Common UV colors are blue, green, or purple.

What is the difference between cube and octahedron in fluorite?

Both are crystal habits of the cubic system. A cube has six square faces; an octahedron has eight triangular faces. The shape depends on growth conditions: cubes form at lower temperatures, octahedra at higher temperatures or with certain additives.

What is fluorite used for in industry?

Fluorite is the main source of fluorine, used to produce hydrofluoric acid, refrigerants, and Teflon. It also acts as a flux in steelmaking, lowering the melting point of impurities. In optics, pure crystals are used for UV and infrared lenses.