Thursday, May 24, 2012

The Chemical Properties of Amethyst

Photo Source: SandAtlas

by Angela Magnotti Andrews

Throughout the 19th century, experts believed that deposits of manganese were responsible for the purple tones that set amethysts apart from other quartz crystals. After the later discovery that heat alters the color of the crystals, chemists and physicists began searching for a new explanation for the purple hues. Scientists now report that iron deposits situated in specific locations within the crystal structure provide the key to their color.

Since iron deposits usually result in reds or browns, the question remains: How is it that amethysts are purple? The answers to this question are found in the silicon-rich hydrothermal liquid in which amethysts are birthed. Geologists conclude that this rich liquid must be infused with uranium particles in order to produce the radiation necessary to oxidize the iron, the process necessary to transform the usual reddish-brown color of iron to the violet hues.

Heat and radiation, both of which play a key role in the formation of amethyst, can also oxidize the iron further, resulting in shades of green, orange, or red. Intense heat or radiation can even drain the color completely from the crystals. Conversely, other colors of quartz crystals can be irradiated, synthetically or naturally, to elicit the purple hues of amethyst. There is currently no way to determine if an amethyst is naturally or synthetically altered by heat or irradiation; however, it is this very treatment that keeps amethyst’s beautiful sister stones, citrines, affordable in fine jewelry.

Read More About Amethysts

1. Oldershaw, Cally. Firefly Guide to Gems. Ontario: Firefly Books Unlimited, 2003, 154-55.
2. "Amethyst Mineral Information." Gem & Mineral Miners, Inc. Last updated November 5, 2011. Accessed May 21, 2012.
3. "Amethyst." Wikipedia. Accessed May 21, 2012.
4. Rolph, Jolyon, and Ida Chau. "Amethyst." Mindat. Accessed May 21, 2012.
5. "Amethyst." The Quartz Page. Last modified November 13, 2011. Accessed May 21, 2012.

*Victorian clip art courtesy of The Graphics Fairy

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