Fluorite

Hardness of 4 on the Mohs scale, colors vary widely (green, purple, blue, yellow, clear), vitreous luster, isometric crystal system, perfect octahedral cleavage, specific gravity of 3.18.

Formed in hydrothermal veins, often associated with metallic ores like lead and zinc, as well as in cavities in sedimentary rocks.

Used in metallurgy as a flux, in the manufacture of optical equipment (lenses), and heavily collected as mineral specimens and carved into decorative objects.

Fluorite is the mineral reference for a hardness of 4 on the Mohs scale. It exhibits strong fluorescence under ultraviolet light, a phenomenon named after the mineral itself.

Easily identified by its relatively low hardness (can be scratched with a knife but not a fingernail), perfect cleavage, and often vibrant cubic or octahedral crystal forms. Found worldwide with notable deposits in China, Mexico, South Africa, and the UK.