Quartz: from German word "Quarz", is the second most common mineral in the Earth’s continental crust. It is made up of a lattice of silica (SiO2) tetrahedra and has a hardness of 7 on the Moh’s scale. Quartz goes by an array of different names. The most important distinction between types of Quartz is that of macrocrystalline (individual crystals visible to the unaided eye) and the microcrystalline or cryptocrystalline varieties (aggregates of crystals visible only under high magnification), often referred to as "Chalcedony".