FORMATION OF GEMS AND STONES

Gems and stones are formed in rocks and sediments. Each mineral or mineral group has a precise chemical composition, made of the same elements or chemical ingredients. These ingredients are given in its chemical formula- the chemical code that defines the mineral and the elements from which it is made.

In addition to the main elements there may be other elements that do not appear in the chemical composition; these accessory elements may affect the properties of the mineral, such as the colour. For instance, the corundum family, which includes Ruby and Sapphire, has a very simple chemical composition (Al203)- two atoms of aluminum (Al) joined with three atoms of oxygen(O). pure corundum would be colourless, but nature seldom enables pure or perfect gemstones to form, so corundum is usually coloured. Chromium and vanadium are accessory elements that give ruby its red colour, iron and titanium give sapphire its blue colour, and other combinations give rise to the many other colours of sapphire such as green, yellow, and pink.

Changes in the surrounding temperature or pressure may affect the concentrations and compositions of the fluids in which some gemstones are formed. Accessory elements may be available during formation of the gemstones or at intervals dependant upon the prevailing environmental conditions.

The variation in elements available during formation may result in a gemstone having an irregular growth or colour pattern. Concentrations of colour, in growth zones or straight bands, can sometimes be seen in gemstones such as rubies and sapphires. The formation of a gemstone may be interrupted, growth may be sporadic, and there may be even be intervals during which the gem detiorates, or is partly dissolved, before growth continues. A gemstone may contain crystals of a different mineral within it. These inclusions may be formed before or after or at the same time as the host. they may be seen as flaws that detract from the beauty of the gemstone or feature that actually enhance the gem, as in the case for rutilated quartz.

Rocks are made of minerals, but not all minerals form crystals that are large enough or in good enough conditions or clear enough of cracks and unattractive inclusions, to be used as gemstones. Gemstones form in the three main rock types: igneous, sedimentary and metamorphic rocks. The formation of rocks is a continuous cycle of events. The rock cycle follows the changes through which rock progresses from its initial formation, being broken down into smaller fragments by wind, rain and snow weathering, transported down rivers and streams(erosion), and finally deposited in riverbed sediments and the sea. These sediments may then form new rock types and the cycle continues.

Google
Powered By Blogger

http://rpc.technorati.com/rpc/ping

http://rpc.technorati.com/rpc/ping