Density: 2.65 / Hardness: 7 / Varieties: Smoky quartz (light to dark brown), Citrine (yellow), Rock crystal (colourless), Amethyst (violet).
Hexagonal prism surmounted by two complementary rhombohedra showing different developments : quartz is sometimes in massive veins.
Transparent to translucent, colorless to milky white, more rarely brownish to black, pink, yellowish or green, greasy to vitreous luster. No cleavage, conchoidal break, prismatic faces often striated perpendicularly to the prism axis.
They are found as shapeless grains in granites and gneisses, as beautiful crystals in the fissures of silica-rich eruptive rocks and crystalline shales, in hydrothermal veins and pegmatites.
Quartz has many origins.