Fluorite

Physical Properties

Hardness: 4 (Mohs scale); Color: Typically blue-green, purple, or colorless; Luster: Vitreous (glassy); Crystal structure: Isometric/Cubic; Cleavage: Perfect octahedral in four directions; Specific Gravity: 3.175 to 3.56.

Formation & Geological History

Formed as a late-stage mineral in igneous rocks, in hydrothermal veins (particularly those containing lead and zinc minerals), and in some sedimentary rocks like limestone. It occurs in a wide variety of geological environments.

Uses & Applications

Used as a flux in steel and aluminum smelting; source of fluorine for hydrofluoric acid; secondary gemstone/ornamental material; high-clarity lenses for telescopes and cameras.

Geological Facts

Fluorite is famous for its wide range of colors and its fluorescence under UV light. It is the definitive mineral for hardness 4 on the Mohs scale. Historically, it was used to carve decorative vessels known as 'Blue John'.

Field Identification & Locations

Identify by its moderate hardness (can be scratched by a knife but not a copper penny) and its distinctive four-way cleavage. Commonly found in Illinois (USA), China, Mexico, and England. Collectors look for well-defined cubic crystals or zoning.

Identified on: 4/23/2026

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