The Mohs Hardness Scale
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| Diamond | Corundum | Topaz | Quartz | Feldspar |
| 10.0 | 9.0 | 8.0 | 7.0 | 6.0 |
| Apatite | Fluorite | Calcite | Gypsum | Talc |
| 5.0 | 4.0 | 3.0 | 2.0 | 1.0 |
According to this scale, a gemstone can only be scratched by another gemstone (or mineral) which has a higher rating. For example, corundum can be scratched by a diamond and topaz can be scratched by corundum and diamond.
It is important to note as well that this scale is not linear, (meaning that a diamond is not 10 times harder than talc), it is only a measure of resistance to scratching. In fact the name of the scale can be very misleading, because even though a gemstone has a high hardness rating does not mean that the gemstone is durable.
For most gemstone wedding rings or engagement rings, it is best to choose gemstones which have a hardness rating of at least 7.0 or above. As quartz (with a hardness rating of 7.0) is one of the most abundant minerals on earth (small pieces are even found in household dust), gemstones with a rating of less than 7.0 can become scratched through average daily wear. While there are a few exceptions to this rule, (such as the pearl with a hardness rating of 3.5 - 4.0) this is a good guideline to start out with.
Other factors which affect a gemstone's overall durability include: cleavage, chemical bonds, stability, and whether or not the gemstone has received any treatments or enhancements. All of these factors together, including the gemstone's rating on the Mohs hardness scale, will give a clear picture of how durable the gemstone really is.
- Cleavage is a gemstone's ability to have a clean break along a distinct line. For example, diamonds have perfect cleavage; this means that a diamond can be split by one blow if it is hit in a specific area. Cleavage is a special concern when a gemstone is being cut or polished, and if you have your gemstone cut or polished by someone who is not experienced with cleavage your gemstone could be ruined.
- A gemstone's stability depends on how well the gemstone holds up to environmental influences such as heat, sunlight, and chemicals. Some gemstones, such as unheated amethyst, can lose their natural color if they are exposed to sunlight or heat. Other gemstones lose their durability when they have been treated with an enhancement; for example, rubies that have been dyed with colored oils have a very poor stability rating and will quickly lose their color.
- The chemical bonds or crystalline structure within a gemstone will also affect a gemstone's durability; emeralds have a hardness rating of 7.5 - 8.0 but their overall durability is poor to good because the stones often have cracks and fissures and can easily chip - while Jade has a hardness rating of 7.0 but an excellent durability rating due to its strong chemical structure which withstands chipping, fractures, or breaks.
So how can you find a durable gemstone? Always take into consideration the gemstone's rating on the Mohs hardness scale, but remember that this rating is only one small piece to the durability of your gemstone. Make sure that you are aware of any treatments or enhancements which can affect the gemstone's stability, if the gemstone has special cleavage considerations when it is cut or polished, and which ring settings will best protect the type of gemstone you are considering.
To make sure your gemstone lasts for many years to come, always check any special care advice which will help to prevent damage from occurring to your gemstone ring.
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