mineral

Fluorite (Polished Egg / Blue John style)

Calcium Fluoride (CaF2)

AI-generated identification · may be incorrect

Hardness: 4 on the Mohs scale; Color: Purple, violet, clear, yellowish, and dark banded zones; Luster: Vitreous to sub-vitreous; Crystal system: Isometric (cubic); Cleavage: Perfect octahedral in four directions; Specific gravity: ~3.18

Hardness: 4 on the Mohs scale
Color: Purple, violet, clear, yellowish, and dark banded zones
Luster: Vitreous to sub-vitreous

Identified October 3, 2026More mineral →

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Physical properties

Formation & geological history

Formed through hydrothermal fluid activity in veins and fractures, typically in association with lead, zinc, and silver ores or in limestone host rocks.

Uses & applications

Carved and polished as ornamental objects (eggs, spheres), cabochons, and mineral display specimens. In industry, unshaped fluorite (fluorspar) is utilized as a flux in smelting and to manufacture hydrofluoric acid.

Geological facts

Fluorite gave its name to the phenomenon of fluorescence due to its glowing response under ultraviolet light. The banded purple-yellow variety is famously known as 'Blue John' from Derbyshire, England, though banded specimens are also mined in China and Mexico.

Field identification & locations

Identifiable by its relatively low hardness (easily scratched by a pocket knife or glass), distinct perfect octahedral cleavage planes often visible internally, and rich purple zoning. Famous deposits include China, Mexico, England, and the United States (Illinois).