Quartz is the second most abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of silicon/oxygen tetrahedra, with each oxygen being shared between two tetrahedra. 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. Color: Transparent, Semi Transparent, Pink.