Amethyst. Credit: Mineral Information Institute.
Amethyst is a variety of quartz, differing from common quartz (or rock-crystal) chiefly in its beautiful violet-blue or purplish violet color – well known as amethystine – which is due to the presence of a little iron oxide or, possibly, manganese oxide. It is one of the most valued varieties of quartz, and is much used for rings, etc, although, being comparatively abundant, it is much inferior in price to the true gems. An amethystine tinge is frequently to be seen in specimens of quartz which are not perfect amethyst. The tinge is often very faint, and is frequently confined to the tips or edges of crystals.
Amethyst is found chiefly in Brazil, Uruguay, Russia (the Urals), Canada (Ontario) and the United States (Arizona and North Carolina). It is, however, a common mineral in Europe. Some of the finest specimens have been found in India, Sri Lanka (previously Ceylon), and Brazil. It is often found lining the interior of balls of geodes of agate, and in veins and cavities in basalt, dolerite (diabase), and other igneous rocks.
The ancients imagined amethyst to possess the property of preventing intoxication, and people addicted to drinking therefore wore in on their necks. The named is derived from a Greek word which signifies unintoxicated.
Not to be confused with amethyst is a mineral called oriental amethyst, which is a variety of spinel having an amethystine color, and is a very valuable gem.