Some amethyst found in Poland can be irradiated to produce prasiolite. An amethyst deposit in Arizona also contains material that can be heat-treated to prasiolite. Most prasiolite entering the gem market today is made by heating amethyst and yellow quartz from the Montezuma deposit in Minas Gerais, Brazil. Only a few amethyst localities in the world are known to have amethyst that converts to prasiolite upon heating. Amethyst Deposits Suitable for Making Prasiolite Some people don't care for the green color and think that heat treatment destroys good amethyst. Some people enjoy this green color and prefer it over purple amethyst. This is the material that forms prasiolite upon heating. These materials are sold as heat-treated citrine.Ī small number of amethyst deposits contain material that turns a yellowish green to green color at about 500 degrees Celsius. Most amethyst turns yellow when heated to about 470 degrees Celsius, then to a dark yellow or reddish brown at about 550 degrees. However, if it is heated to high temperatures, the color can change. This color is stable under most conditions at Earth’s surface. The purple color of amethyst is caused by trace amounts of iron or iron mineral inclusions within the quartz. The name "prasiolite" is derived from two Greek words: prason, which means "leek" and lithos, which means "stone." Other names used for prasiolite are "praseolite" and "praziolite." It is pronounced "PRAYS-ee-oh-light." For more information, see our article about "green amethyst" and "yellow emerald". Sellers who continue using the name "green amethyst" could face legal action. In those guides they state that the name "green amethyst" is "incorrect", and that use of the name can be "misleading", "unfair", and "deceptive". In July 2018, the Federal Trade Commission of the United States published a new edition of their Guides for the Jewelry, Precious Metals, and Pewter Industries.
Federal Trade Commission on "Green Amethyst" That makes "green amethyst" an incorrect name, just as "yellow emerald" and "red emerald" are misnomers for " heliodor" and " red beryl," respectively. Amethyst, by definition, is a purple variety of quartz. "Green amethyst" is a misnomer (an incorrect name) that some people use for prasiolite. It is found where an amethyst-bearing rock unit has been heated by younger lava flows or nearby intrusions. Naturally Heated Amethyst: Another small amount of amethyst is heated by natural processes. The green color is often unstable and can fade to colorless if the stone is exposed to temperatures over about 150 degrees Celsius. This produces prasiolite with a light green color. Irradiated Amethyst: A small amount of prasiolite is produced by irradiating natural amethyst.
This heating changes the amethyst's color from purple to green or yellowish green. Heat-Treated Amethyst: Most prasiolite is produced by heating natural amethyst in a laboratory oven to about 500 degrees Celsius. It is produced by the three processes described below: Prasiolite is a yellow-green to green variety of quartz that is cut into faceted stones for use in jewelry or purchased by gemstone collectors.
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