What are the three components of durability?
Durability is a gemstone's ability to withstand wear, heat, and chemicals. It varies from gem to gem, depending on chemical composition and structure. Durability consists of three properties:
- Hardness
- Toughness
- Stability
In gemology hardness and toughness have specific, separate meanings. Hardness means resistance to scratching, how a stone’s surface responds to contact with a sharp point to the edge of another object, to abrasive powders or to another gem. Toughness means resistance to breaking, chipping or cracking, how well a stone can survive impact from a fall or a blow.
Jade, for example, is very tough but not very hard. It can’t easily be broken, but it’s soft enough to be carved with simple tools. A diamond, on the other hand, can only be broken with a blow in the right place. But it’s so hard that it can only be scratched by another diamond.
Hardness
The Mohs scale (pronounced MOZE) rates the hardness of gems and minerals. The scale originated in 1822 when Friedrich Mohs chose ten minerals and assigned numbers to them, based on the relative ease or difficulty with which one could be scratched by another. His studies resulted in this scale:
- Diamond 10
- Corundum 9
- Topaz 8
- Quartz 7
- Orthoclase Feldspar 6
- Apatite 5
- Fluorite 4
- Calcite 3
- Gypsum 2
- Talc 1
The Mohs scale is deceptive. The steps between the minerals are not evenly spaced. Diamond is only one number away, but it’s many times harder than gems in the corundum family.
Toughness
Any stone, including a diamond, will fracture if it’s hit hard enough in the right place. Toughness is a measure of how well a gem can survive an impact and resist breaking, chipping, or cracking. A gem’s toughness is a function of its structure. The way diamonds form affects their physical and optical qualities. When the atoms come together under extreme temperature and pressure conditions, they bond to each other more tightly in some directions than they do in others.
Stability
Stability is a term that describes how well a diamond resists temperature changes and chemicals. Diamonds are very stable. They’re invulnerable to virtually all acids, for one thing. The cutting process generates a lot of heat, but diamonds usually endure intact. Situations that are more threatening to a diamond’s stability are those that involve sudden and extreme temperature changes. Those changes can cause thermal shock, which can create new fractures and cleavages or cause existing ones to spread.Diamonds will burn at about 1562°F (850°C). House fires and jewelers’ torches can reach that temperature, burned diamonds look white and cloudy.
Source: Gemological Institute of America
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