Fluorite (calcium fluoride) is one of the most coveted collector minerals for good reason: the color variety is extraordinary — purple, blue, green, yellow, pink, colorless, and banded combinations of all of them. Its defining field test is octahedral cleavage: a broken piece naturally produces eight-sided fragments, unique among common minerals. Many specimens glow blue or purple under shortwave UV light, but fluorescence varies so much by locality that a UV lamp alone is not a reliable field ID tool. Hardness 4 means a steel knife scratches it easily.
The mineral that named the glow
Fluorescence is named for fluorite, whose blue-violet response under ultraviolet light was described long before anyone could explain it. Not every fluorite fluoresces — activator impurities do the work — so a dark lamp test is corroboration, never the whole identification. Octahedral cleavage and hardness 4 remain the dependable cues in daylight.