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Gemstone Properties
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Gems have other properties which help define their true worth and validity. If looked at in details many of the terms are very technical but non-the less serve as a means of comparison between one type of gem and another (or indeed help identity a fake!)
• Specific Gravity – defines the density of the gemstones relative to the density of water. This measurement – like many other – means little in its own right but is a means of comparing one item with another.
• Cleavage is a terminology used in the description of natural and man made substances. In the context of gems cleavage describes ‘how’ the gem stone is likely to split creating smooth surfaces on each side of the ‘break’. If you look at a crystal you can possibly visualise how the crystal would separate into different ‘planes’. A complex crystal form may easily split in several different forms – diagonal cleavage is different to a cubic cleavage – simply because of the ‘natural’ way to separate into different planes.
• Fracture – much as you would expect. Natural rocks and minerals have cracks or fractures.
• Lustre – is just a means of describing how light reacts with the gems and the type of appearance the gem displays. Again there are many more technical descriptions of words to describe the ‘lustre’. A material may display high gloss lustre or a matt lustre.
• Refractive Index – The speed at which light travels is approximately 186,000 miles per second (just under 300,000 kilometres per second|) when travelling through the atmosphere. The speed changes when passing through a material such as glass – the speed is slowed down. Hence the refractive index of light through glass is a number or constant which can be referred to and measured and compared to other materials which allow the passage of light.
• Dispersion - yet another technical term to define how light if effected by its path through the gem. If you hold a diamond to the light then you can frequently see a ‘rainbow effect’ – i.e. the light is dispersed through the gem. (a real rainbow is caused by the light passing through water – i.e. rain which disperses the light .
Gems are classified into different groups, species, and varieties. For example, ruby is the red variety of the species corundum, while any other colour of corundum is considered sapphire. Emerald (green), aquamarine (blue), heliodor (yellow), and morganite (pink) are all varieties of the mineral species beryl.
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See Peter
Williams @ The Article Sense
and also My Hampshire Blog
& Information Guide
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