QUARTZ

Quartz is a crystalline rock or mineral composed of silicon dioxide. Quartz is the second most common mineral in the Earth's continental crust and found in all types of geological environment. There are 49 variety's, a number of which are gemstones, some of which are very beautiful and very rare. Origin of name from Saxon word Querkluftertz = cross-vein ore.
Colour: colourless, white, gray, yellow to brown to black, violet, pink
Hardness: 7