Quartz is a crystalline form of silica. The greatest concentrations of quartz are found in silica-rich igneous and metamorphic rocks. Often transparent, Quartz can be found in almost any color. Quartz has piezoelectric properties, meaning it generates an electric charge in response to pressure.
Chemical composition: SiO2; Hardness: 7
Phantoms are formed when another mineral drops onto a crystal during its growth. The crystal continues to grow, encompassing the foreign mineral which is now in the shape of the crystal during an earlier stage.