Rainbow fluorite

A polished, banded specimen showing pale purple and green zoning; vitreous luster and cubic crystal structure, though the cut surface hides crystal form. Mohs hardness 4, perfect octahedral cleavage, and specific gravity about 3.18.

Forms mainly in hydrothermal veins and replacement deposits when fluorine-rich fluids precipitate calcium fluoride, commonly alongside quartz, calcite, and galena. The specimen’s exact geological age cannot be determined from the image; fluorite deposits range from Precambrian to recent geological periods.

Used industrially as a flux in steel and aluminum production and as a source of hydrofluoric acid; transparent colorful material is cut for cabochons, carvings, and display specimens.

Purple coloration commonly reflects radiation-related color centers or trace impurities, while green bands arise from differing trace-element chemistry. Fluorite is the official Mohs hardness-4 reference mineral.

Identify by its unusually low hardness, strong cleavage, cubic habit, and purple-green color zoning; a steel knife can scratch it. Important localities include China, Mexico, England, Illinois, and parts of Spain.