Amethyst crystals, cut gem, and beads

February’s birthstone is amethyst, the purple variety of quartz.

Last month I told you about the many different colors of garnets, which are caused by differences in chemical formula. Pure quartz (chemical formula SiO₂) is colorless (and is called “rock crystal” in the jewelry industry). The different colors of quartz* are caused by defects in the crystal structure rather than by a consistent change in the  chemical formula. This often causes different amounts of color within even a single crystal (“color zoning”). For amethyst, iron, and possibly aluminum, impurities are believed to cause the purple color.

Amethyst deposits are found all over the world; many of the large mineral specimens come from Brazil and Uruguay, but other sources for the gem include Russia, Czechoslovakia, Zambia, and the United States. It is not uncommon to find relatively large crystals which makes this a very affordable gem, even in large sizes.

Other facts – Amethyst:

• is the gemstone for those celebrating their 6th or 17th wedding anniversary
• was believed to prevent intoxication—amethystos means “not drunk” in ancient Greek
• is sometimes found in combination with citrine and is then known as “ametrine”
• when heated can change color to become a golden citrine
• has a hardness of 7 on the Moh’s scale

*Other quartz gemstones include citrine (yellow), aventurine (green), rose quartz (pink), tigers eye (brown), smokey quartz (brown or gray) and chalcedony (which includes jaspers and agates).

Sources:

• Gemological Institute of America, Gem Encyclopedia page on amethyst: click here.
• Manual of Mineralogy, 20th Edition, Cornelis Klein and Cornelius S. Hurlbut, Jr., 1977.
• GemSelect