It is the most common mineral in the earth's crust after feldspar.
It has been suggested that its name comes from German, which in turn derives from the Old Slavonic word for hard.
The ancient Greek word for quartz, krystallos, gave rise to the word crystal.
Quartz occurs in 2 basic forms: Macrocrystalline quartz: It is made of visible crystals or grains. Examples: rock crystal, sandstone, also massive quartz composed of crystals without crystal faces. Microcrystalline quartz: It is made of dense and compact aggregates of microscopic quartz. The different types of microcrystalline quartz are subsumed under the term chalcedony. Examples: Agate, Flint...