Quartz is the second most abundant mineral in the Earth's continental crust (after feldspar). It is made up of a framework of silicon-oxygen tetrahedra SiO4, with each silicon shared between two oxygens to give the overall formula SiO2. Quartz has a hardness of 7 on the Mohs scale and a density of 2.65 g/cmÂ³.
A major variety Rock crystal Clear, colorless
Although many of the varietal names historically arose from the color of the mineral, current scientific naming schemes refer primarily to the microstructure of the mineral. Color is a secondary identifier for the cryptocrystalline minerals, although it is a primary identifier for the macrocrystalline varieties. This does not always hold true.