What Crystal System Is Amethyst?
An amethyst is actually a quartz, its characteristic violet color due to trace amounts of ferric iron. If heated to 300 degrees Celsius, an amethyst will turn white. At higher temperatures, of 500 degrees Celsius, an amethyst turns yellow (into citrine). But it will return to violet if exposed to X-rays or is bombarded with alpha particles. The most beautiful amethysts are mined from Brazil. Amethysts also come from Uruguay, Sri Lanka, Canada, the U.S., Germany, Australia, the Urals, Zambia, and the Czech Republic.
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Crystal System
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All quartz, amethysts included, belong to the hexagonal crystal system. This gemstone may occur in well-formed crystals that can be as large as 289 pounds. Or they may form in compact masses. The crystals are typically hexagonal and prismatic, the ends terminated by two rhombohedra, which resemble hexagonal dipyramids. The prism faces can contain horizontal striations. Crystals may also contain bubbles of liquid or gas that is visible to the eye.
Cystal Properties
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Quartz crystals are hard, measuring a 7 on the Mohs scale. It is a lightweight stone that ranges from transparent to translucent. Amethyst is said to have a vitreous luster. There is no cleavage, but it produces good conchoidal fractures. Quartz crystals have the ability to rotate the plane of polarization of light that passes through it.
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Enviroment
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Amethysts are found in geodes and in alluvial deposits. Some of the largest geodes with amethysts inside are found in Brazil. In fact, quartz is one of the most common minerals found in the Earth's crust. It crystallizes from igneous magma sources.
Uses
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Poor quality amethysts are often tumbled to make beads. When the stone's impurities do not give it a strong color, pale stones may be put in a closed setting or have foil behind it to enhance its color. Imitation amethysts are made from glass and synthetic corundum.
Other Varieties of Quartz
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Other gemstones related to amethyst, being quartz themselves, include: milky quartz, rock crystal (pure quartz), smoky quartz, blue quartz, citrine, rose quartz, tiger's eye, rutilated quartz, and aventurine. Each of these varieties are due to different impurities or, in the case of rock crystal, no impurities.
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References
- Photo Credit Amethyst image by photoBeard from Fotolia.com
