Gems - Mineral Crystals Part I
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Gems, precious crystals, rainbow hued fire. Mankind has long sought these precious rocks, often delving deep into the earth; often fighting and bleeding to wrest the gleam from the ground or from another man’s hand. Gems are firmly rooted in our human history. So, what are gems?
Gems are rare mineral crystals valued for their beauty. Historically, gems have been classified as either precious or semi-precious stones. The definitions of precious and semi-precious stones have changed over time and according to culture. For example, the ancient Greeks thought amethyst was a precious stone; however, today amethyst is regarded as a semi-precious stone because we’ve found so many of them in South America.
Today, when people talk about precious gems they are usually referring to diamonds, rubies, sapphires, and emeralds. Sometimes pearls (not really a mineral but still called a gem), and opal are considered to be precious gems. It’s misleading to classify gems as either precious or semi-precious. For example, garnet is a semi-precious stone but green garnet can be far more valuable than the same size mid quality emerald. It’s all very confusing. That’s why it is better to use other ways to classify gems.
The best way to classify gems is based on their physical properties. Gems are made from different chemicals and minerals. Because they are made from different things, gems have different physical properties. If you can figure out what a gem is made from you can figure out what kind of gem you have. Diamonds are made from carbon. Rubies and sapphires are made from the mineral corundum. Emeralds are from the mineral beryl and amethysts from the mineral quartz. Rubies have tiny amounts of the element chromium that makes them red. Sapphires are gem quality corundum in any color other than red. Sapphires have tiny amounts of other chemicals that change the color of the crystal. Other gems are made from different mineral crystals.
Remember, sapphires and rubies are made from the same mineral. It could be confusing to tell them apart unless you can see the color of the gem. Color is one way people can tell one gem from another. However, you can’t just use color, there are green garnets and green emeralds. You have to use more than one test to tell one gem from another. There's a big long list of different properties and tests for each of them. There is an entire branch of science that studies gems. The science is called gemology and the scientists are called gemologists. There are laboratories around the world that classify gems, and grade their quality.