Quartz is a hard, crystalline mineral composed of silicon and oxygen atoms. It is the second most abundant mineral in Earth’s continental crust, behind feldspar. As a mineral name, quartz refers to a specific chemical compound (silicon dioxide, or silica, SiO2), having a specific crystalline form (hexagonal).
Its unique properties make it one of the most useful natural substances. It is found in all forms of rocks: Igneous, metamorphic and sedimentary.
Quartz is physically and chemically resistant to weathering.