MARK A. SCHNEIDER / SCIENCE PHOTO LIBRARY MARK A. SCHNEIDER / SCIENCE PHOTO LIBRARY
Fluorite and quartz. Crystals of the minerals fluorite (or fluorspar, blue) and quartz (red), fluorescing under shortwave ultraviolet light. Fluorite is composed of calcium fluoride. It occurs in many colours due to the presence of trace elements. It is used in processing steel and aluminium, and by the chemical industry to make hydrofluoric acid and fluoride compounds. Quartz is composed of crystalline silica (silicon dioxide). It is very common and extremely hard. It is a component of nearly all rock types and is found in almost every geological environment.
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