Amethyst is a purple variety of quartz often used as an ornament. The name comes from the Greek a ("not") and methustos ("to intoxicate"), a reference to the belief that the stone protected its owner from drunkenness; the ancient Greeks and Romans wore amethyst and made drinking vessels of it in the belief that it would prevent intoxication.ChemistryAmethyst is the purple variety of quartz, its chemical formula is SiO2.In the 20th century, the color of amethyst was attributed to t