But what is a gemstone ?
A gemstone or gem (also called a fine gem, jewel, or a precious or semi-precious stone) is a piece of mineral crystal, which, in cut and polished form, is used to make jewelry or other adornments. However, certain rocks (such as lapis lazuli) or organic materials that are not minerals (such as amber or jet), are also used for jewelry, and are therefore often considered to be gemstones as well.
The first characteristic a gemologist uses to identify a gemstone is its chemical composition.
There are over 130 types of minerals that have been used as gemstones (amethyst, fluorite, garnet, jasper, turquoise...). For example amazonite, labradorite, moonstone and sunstone are part of the Feldspar species.
There are a number of organic materials used as gems, including amber, bone, coral, ivory, jet, other of pearl, pearl, petoskey stone.
There are also a number of rocks used as gems, including lapis lazuli, obsidian or unakite.
(Source: Wikipedia)
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