Quartz is the second most abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz, several of which are semi-precious gemstones. Especially in Europe and the Middle East, varieties of quartz have been since antiquity the most commonly used minerals in the making of jewelry and hardstone carvings. The word "quartz" is derived from the German word "Quarz" and its Middle High German ancestor "twarc", which probably originated in Slavic (cf. Czech tvrd ("hard"), Polish twardy ("hard")).Major Varieties of QuartzChalcedonyCryptocrystalline quartz and moganite mixture. The term is generally only used for white or lightly colored material. Otherwise more specific names are used.AgateMulti-colored, banded chalcedony, semi-translucent to translucentOnyxAgate where the bands are straight, parallel and consistent in size.JasperOpaque cryptocrystalline quartz, typically red to brownAventurineTranslucent chalcedony with small inclusions (usually mica) that shimmer.Tiger's EyeFibrous gold to red-brown colored quartz, exhibiting chatoyancy.Rock crystalClear, colorlessAmethystPurple, transparentCitrineYellow to reddish orange to brown, greenish yellowPrasioliteMint green, transparentRose quartzPink, translucent, may display diasterismRutilated quartzContains acicular (needles) inclusions of rutileMilk quartzWhite, translucent to opaque, may display diasterismSmoky quartzBrown to gray, opaqueCarnelianReddish orange chalcedony, translucentDumortierite quartzContains largeamounof dumortierite crystals