Amethyst :

Amethyst is the purple variety of quartz, its chemical formula is SiO2.the color of amethyst was attributed to the presence of manganese.Beads of amethyst are found in Anglo-Saxon graves in England.Purple corundum, or sapphire of amethystine tint, is called Oriental amethyst, but this expression is often applied by jewelers to fine examples of the ordinary amethystine quartz,even when not derived from eastern sources. Professional gemological associations, such as the Gemological Institute of America (GIA) or the American Gemological Society (AGS),discourage the use of the term "Oriental amethyst" to describe any gem, as it may be misleading.

Traditionally included in the cardinal, or most valuable, gemstones (along with diamond, sapphire, ruby, and emerald), amethyst has lost much of its value due to the discovery of extensive deposits in locations such as Brazil.