As a mineral name, quartz refers to a specific chemical compound (silicon dioxide, or silica, SiO2), having a specific crystalline form (hexagonal). There are other forms of silica which are either non-crystalline, or of a different crystalline form than quartz.uartz is a very common mineral in the Earth’s crust. Chemically, quartz is silica, or silicon dioxide, SiO2. It is found in most types of rocks: igneous, metamorphic and sedimentary. Quartz is rather hard, 7 on the Moh’s hardness scale, and has a glassy (vitreous) luster.