Why it is important to know about the hardness of your stone (3 of 5)

Monday, June 7, 2010

Another important characteristic of a precious gem stone is durability. How hard and how tough is your stone? Often people think that these words are the same characteristic of durability of a stone. It is wrong.

For example, diamond is the hardest stone on the Earth. Though, it can cleave. Opposite, jade can be easily scratched, but you cannot split it.

By the way, all the minerals can be ranged in an order by their hardness. The Austrian mineralogist Friedrich Mohs has created the scale of hardness. He selected 10 common and easily obtained minerals, with quite distinctive hardness, as the comparison minerals. The harder a mineral is, the higher number it has in the scale. A harder mineral can scratch a softer mineral.

1- Talc (can be crushed with a finger nail)
2- Gypsum (can be scratched with a finger nail)
3- Calcite (can be scratched with a copper coin)
4- Fluorite (can be easily scratched with a knife)
5- Apatite (can be scratched with a knife)
6- Orthoclase feldspar (can be scratched with a file)
7- Quartz (can scratch glass)
8- Topaz
9- Corundum
10- Diamond

This is only an order of hardness, but the scale does not show how much one mineral is harder than another. Nevertheless, it is very useful to know about the hardness of your stone.

It is considered that only the gem stones with the hardness 7 or higher can be called precious, because they are durable. You might think that this is not the rule anymore in our century of plastic and other jewellery made of disposable materials, but the hardness keeps influencing the prices of the gems. Therefore, the amethyst (with its hardness 7, as it is quartz) is going always be more expensive than the violet fluorite that looks practically the same (except its hardness is 4).

Consider the hardness when you are trying to keep your gem stone jewellery in a perfect condition. Put the jewellery pieces with the gems of different hardness into the separate boxes or the harder gems will scratch the softer stones.

Maria Roudakova
A jeweller from Switzerland


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