Gems also known as Precious Stones

     Precious stones, or gems, are minerals used for adornment, and they are found in rocks. Rocks are divided into three groups. The igneous (fire-formed) rocks may be fine-grained or coarse-grained; a very coarse-grained type, called pegmatite, is an important source of gem minerals such as diamonds. Gems are also found in the cavities of the igneous rocks granite and obsidian.

     Sedimentary rocks are layered rocksand, exceptforturquoiseand opal, are the source of very few gems. However, when the original rock contained heavy minerals-and gem minerals are heavy-pebbles of them tended to be deposited as pebbles in a river bed and such deposits form the gem gravels of Upper Burma, the "byon", and those of Ceylon, the "illam".

Metamorphic rocks - rocks which have been altered by pres­sure—are a fruitful source of gem minerals, for instance the rubies found in Burma.

There are also precious materials of animal origin—pearls from oysters, ivory from elephants and coral from the tiny sea creatures which give their name to it. There are also amber and jet, whose origin is vegetable. Amber is the fossilized resin of a coniferous tree which grew in the Eocene period. Jet is a variety of fossil wood.

Gems are found throughout the world and are prized for their rarity and beauty. Their charm may depend on transparency and depth of colour as in the ruby and emerald, on colour only as in the turquoise, on purity and "fire" as in the diamond, and on "play of colour" as in the opal.