Rock IdentifierFluorite
Key takeaways
- Fluorite is calcium fluoride, Mohs 4, with famously perfect octahedral cleavage.
- It comes in every color and often shows color banding within a single crystal.
- It gave its name to 'fluorescence' — many specimens glow under UV.
What it is
Fluorite (calcium fluoride, CaF₂) is a favorite for its glassy cubic crystals and astonishing range of colors — purple, green, blue, yellow, pink, and colorless, sometimes several banded within one crystal. It's a moderately soft mineral at Mohs 4, easily scratched by a knife.
How to recognize it
Two features stand out: cubic crystals and perfect cleavage in four directions, so broken pieces often step down into octahedra with flat, mirror-like faces. Combined with its softness (much softer than similar-looking quartz or amethyst, which are hardness 7), the cubes and cleavage make fluorite fairly distinctive. Its luster is glassy and it's often beautifully transparent.
Fluorescence & care
Fluorite is the mineral that gave fluorescence its name — many specimens glow blue or purple under ultraviolet light. Because it's soft and has easy cleavage, it chips and scratches readily; handle it gently, keep it from harder minerals, and avoid ultrasonic cleaners. Some fluorite also fades slightly with prolonged strong sunlight.
