This is measured on the Mohs scale.
The hardness of a gem has a bigger influence on a gem’s appearance than you might realise.
I am not just referring to durability. However, let’s start with durability. A gem’s hardness is one of three measurements that will determine how long you will gain pleasure from your gemstone. The harder a gem is the more it will withstand scratches and abrasion. To understand how well your gemstone will stand up to scratches find out its hardness (each gem featured in this book has a chart where the hardness is detailed), next read the section on the Mohs scale and be aware of what items could scratch your precious gem.
If your gem measures less than 7 on the Mohs scale, even if you are really careful not to scratch it, at sometime during your life you may have to have it re-polished by a lapidarist as airborne dusts which are normally full of silica and quartz will eventually abrase softer gems such as Apatite and Fluorite.
The harder a gem, the more closely knit are its atoms and molecules and the more lustre and brilliance you are likely to see. The harder a gem is, the more likely it will be transparent.
One of the greatest benefits with harder gemstones is the wider array of options the lapidarist has when faceting the gem. The harder the gem, the more defined and acute the angles of facets can be. Whilst softer gems tend to have softer lines between facets, a hard gem such as a Topaz or a Sapphire can have razor sharp line between each surface. This not only adds to the attraction of the gem but also means that scintillation is maximised.
