What is the Mohs hardness scale?
By Jared James · Last updated 21 May 2026
Definition
The Mohs hardness scale is a ranking from 1 to 10 that describes how resistant a mineral or gemstone is to being scratched, where 10 is the hardest and 1 is the softest. Devised by German mineralogist Friedrich Mohs in 1812, it works by testing whether one material can scratch another. Diamond sits at 10, corundum (ruby and sapphire) at 9, topaz at 8, quartz at 7, and talc at 1. For jewellery, the scale is a practical guide to which stones suit everyday rings compared with those better kept for earrings or occasional wear.
Frequently asked questions
- What Mohs hardness is good for an engagement ring?
- A stone worn daily in a ring should ideally rate 7 or above to resist the fine dust and grit in everyday air, which is mostly quartz at around 7. Diamonds at 10, sapphires and rubies at 9 and moissanite at 9.25 are all excellent choices for rings.
- Does a higher Mohs number mean a tougher gemstone?
- Hardness and toughness are different things. Mohs measures scratch resistance, while toughness describes how well a stone resists breaking or chipping. Diamond is the hardest but can chip from a sharp blow. Some softer stones like nephrite jade are actually very tough despite a lower Mohs rating.
- Can any gemstone scratch another?
- A harder stone will always scratch a softer one. Diamond at 10 can scratch every other gemstone. Sapphire at 9 can scratch topaz, quartz and everything below it on the scale. This is also why storing mixed jewellery together can cause damage.
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