The Mohs Scale of Hardness 



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).

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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.

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Gemstone Listing by Mohs Scale Chart           Copyright  Lapigems 2016