A commonly used scale in the trade, it is often misconstrued or misunderstood.
This article explains all!
What is the Mohs Scale ? : The Mohs scale was developed by German mineralogist Friedrich Mohs and is a scale used by gemologists to classify a gem mineral’s resistance to scratching or in other words “the difficulty or ease with which one mineral can be scratched by another”.
The scale assigns each mineral a value between 10 (being the hardest and most resistant to scratching) and 1 (the least resistant to scratching).
Mohs Scale Ranking Chart Copywright Lapigems 2016
Diamond is the only mineral with a value of 10, being the hardest mineral. As the graph above shows, there is a large drop from 10 to 9 where the next hardest minerals are categorized (Ruby & Sapphire). However, the graph is not linear, Diamond is actually 3 ½ times harder than Ruby and Sapphire, which in turn are twice as hard as Topaz.
Hardness vs Toughness
A common misconception made in both the trade and by layman is equating “hardness” which is "the resistance to scratching" to a mineral’s susceptibility to damage as a whole. Minerals are susceptible to damage in different ways - they could break, deform, or crumble instead of scratching. Hard materials often break when subjected to stress. This is a lack of toughness and is assessed using a different scale. Emerald, for example, has a hardness of 8 but its propensity to contain numerous inclusions and fractures can mean that is not very durable in a setting, even though its resistance to scratching is relatively good.
General Listing of Gemstones by Mohs Scale Value
The table below gives a good breakdown of various minerals and their values on the Mohs scale.
Gemstone Listing by Mohs Scale Chart Copyright Lapigems 2016