Quartz (SiO₂) is one of the most common minerals in the Earth's continental crust and forms through direct crystallization from magmas and hydrothermal solutions at relative low-temperature.

Quartz occurs in macrocrystalline (individual crystals visible to the unaided eye) and microcrystalline or cryptocrystalline varieties (aggregates of crystals visible only under high magnification). Macrocrystalline varieties are commonly transparent such as Rock Crystals, Amethyst, Rose Quartz and Citrine.