KouTypin_Dvorak (koo_dvorak)

Quartz is the commonest of the crystalline forms of silicon dioxide. It crystallizes in the hexagonal system, most usually in the form of a six-sided prism surmounted by a six-sided pyramid. It is also frequently found as irregular masses, or as aggregates of small crystals and crystalline grains. It possesses no regular cleavage, but breaks with an irregular and often curved fracture.