The title is a little misleading as I really want to discuss the terms Precious and Semi-precious gemstones. You hear and read statements such as “Diamond, Ruby, Sapphire and Emerald are the only true precious gemstones. The rest are considered semi-precious” or “Emeralds, Rubies, Diamonds, and Sapphires were precious by definition and everything else, regardless of relative value, was semi-precious”. This is now somewhat misleading as it suggests that some gemstones have inferior value. Actually, all stones are now considered precious and their prices are determined by the availability and quality of the gemstone. But, you will still see these terms on a regular basis. I even slip myself, as evidenced in other articles.
The two groups of gemstones are Mineral gemstones and Organic gemstones. Mineral gemstones are naturally growing rocks found in the earth's surface. There are 16 groups of mineral gemstones, including: Beryl, Chrysoberyl, Corundum, Diamond, Feldspar, Garnet, Jade, Lapis Lazuli, Opal, Peridot, Quartz, Spinel, Topaz, Tourmaline, Turquoise, and Zircon. Technically, Lapis Lazuli is a rock and not a mineral but is generally still classified under mineral gemstones.
Organic gemstones are not as durable as gemstones from minerals, and consist of four groups. Amber, a fossil resin found in the sap of ancient tree pines, usually lacks a crystalline structure. It is most often brown or semitransparent and mined. Coral is calcium carbonate extracted from the sea when a small marine animal, known as a coral polyp, uses it to build a protective home for itself. Gem coral ranges from semi-translucent to opaque and can be white, pink, orange, red, blue, violet, gold, or black. Jet is a black fossilized coal that can be used for making beads. Pearl is formed inside an oyster, or any other mollusk that deposits substances inside of its housing. Mollusks creating pearls can be found in either fresh or salt water, but salt water pearls have traditionally been more sought after for use in jewelry. This is changing however, as the Japanese have developed new methods of creating freshwater pearls that are uniform and round -- the 2 greatest attributes of saltwater pearls.
The following link will take you to a fascinating chapter of a book on gemstones. It is very easy to read and extremely informative.
www.secretsofthegemtrade.com/images/chapter2.pdf
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