Fluorite

Hardness: 4 on Mohs scale; Color: This specimen appears dark purple/blue, but fluorite can be colorless, white, purple, blue, green, yellow, or pink; Luster: Vitreous (glassy); Crystal structure: Isometric (cubic); Cleavage: Perfect octahedral; Specific gravity: 3.0-3.3

Fluorite typically forms in hydrothermal veins, often associated with metallic ores. It can also be found in sedimentary rocks and as an accessory mineral in igneous rocks, especially granites and pegmatites. Its formation occurs at various temperatures and pressures. Geologically, it can be found in deposits ranging from ancient Precambrian to relatively modern Cenozoic eras.

Fluorite is used as a flux in steelmaking and other metallurgical processes due to its ability to lower the melting point of raw materials. High-purity fluorite is used in the chemical industry to produce hydrofluoric acid (HF), which is then used in the production of various fluorine-based chemicals, including refrigerants, aluminum, and plastics. Optical-grade fluorite is used for lenses in telescopes, cameras, and microscopes because it has low dispersion (does not scatter light much). It is also carved into ornamental objects and jewelry, though its softness makes it less suitable for everyday wear.

The phenomenon of fluorescence, where a material emits light when exposed to UV radiation, was first observed in fluorite and is named after the mineral. Some fluorite specimens exhibit thermoluminescence (emitting light when heated) or triboluminescence (emitting light when fractured or abraded). Fluorite is often found alongside other valuable minerals like galena, sphalerite, barite, and quartz.

Fluorite can be identified in the field by its relatively low hardness (easily scratched by a knife), perfect octahedral cleavage (it breaks into characteristic eight-sided shapes), and often vibrant colors. The specimen in the image, being a polished sphere, highlights its color and vitreous luster. Common locations include China, Mexico, Mongolia, Russia, Spain, the United States (Illinois, Kentucky), and Germany. Collectors value fluorite for its wide range of colors, crystal habits, and fluorescent properties. Specimens can be found in cubic, octahedral, or dodecahedral forms. For collectors, avoiding exposure to prolonged sunlight is recommended as some colors can fade.