Quartz (SiO2) is the most abundant mineral in the Earth's crust after feldspar. It occurs in an unlimited variety of forms and in countless rock types and mineral deposits. Quartz fits in the trigonal crystal system and well-developed crystals most usually are hexagonal (6-sided) prisms, topped by a 6-sided pyramid. But other habitats are frequent, like the flat columnar type, on this multi-faceted surface. Actual width is 95 mm.