Prasiolite

Prasiolite typically occurs together with amethyst and has been found in metamorphic, igneous and volcanic rocks. Natural finds have been claimed in Brazil, Canada (Thunder Bay), Namibia, Poland, Tanzania, the USA and Zambia. Well-documented occurrences include Farm Rooisand in Namibia, where it occurs with amethyst in a quartz vein, and Płóczki Górne in Lower Silesia, Poland, where olive-green prasiolite lines agate geodes. Most gem material, however, is produced artificially from amethyst or other quartz.

Prasiolite has the gemological constants of quartz: refractive index 1.544–1.553, birefringence 0.009 and specific gravity 2.65. Its colour is usually the result of heating amethyst or of combined irradiation and heating, and some crystals show zones of amethyst colour. The name "green amethyst" is misleading because the stone is not purple and is not amethyst. Mindat advises comparing prasiolite with prase and plasma, and warns not to confuse it with prasolite, a name for a chlorite-group variety.

The colour of prasiolite commonly fades in sunlight, so it should not be left in strong light for long periods. Like other quartz it has no cleavage but is brittle, so protect it from hard knocks.

The name prasiolite comes from Greek and means "leek-green stone". Natural prasiolite was first found in the early 19th century near Płóczki Górne in Lower Silesia, Poland.