Fluorite, Galena & Gypsum
Fluorite
– CaF2
Fluorite
Talc (1)Diamond (10)
Softer than glass. A steel knife scratches it.
Did you know?
Fluorite gave fluorescence its name. In 1852 the physicist George Stokes, studying the mineral's glow under invisible light, coined the word for the whole phenomenon after the stone itself.
Galena was the heart of the first crystal radios. Acting as a natural semiconductor, it let a fine wire called the cat's whisker pull voices from the air with no battery at all.
Gypsum is so soft you can scratch it with a fingernail, yet in Mexico's Naica mine it grew into glassy beams up to 11 meters long, among the largest natural crystals ever found.
