Interactive Mohs hardness scale
Hardness is the first identification test. Tap a level to discover its reference mineral and how to test it at home.
Select a hardness level above.
Hardness: the first test in stone identification
The Mohs scale was devised in 1812 by the German mineralogist Friedrich Mohs, and two centuries on it remains the most widely used field tool in the world for identifying a mineral. Its principle is beautifully simple: it ranks minerals from 1 (talc) to 10 (diamond) by their resistance to scratching. Each level scratches the one below — quartz (7) scratches orthoclase (6), topaz (8) scratches quartz, and nothing scratches diamond except another diamond.
Testing a stone's hardness at home
The great advantage of this test is that it needs no equipment: everyday objects will do. Your fingernail has a hardness of about 2.5 — if it scratches the stone, you are below 2.5 (gypsum, selenite, amber). A copper coin is 3.5; a knife blade or steel nail, around 5.5; a piece of glass, also 5.5; a steel file, 6.5.
The method: try to scratch the stone with each object, from softest to hardest, on a discreet area. Then try the reverse — does the stone scratch glass? If so, it is above 5.5. If it scratches glass effortlessly, you are probably above 7: quartz, amethyst, citrine, agate, tiger's eye. Never perform this test on a cut gem or a collection piece: keep it for rough stones, on a hidden face.
What hardness does not tell you
A classic trap: hardness is not toughness. Diamond, hardness 10, is the hardest natural material — yet it has cleavage planes and will split cleanly under a well-aimed blow. Nephrite jade, at only 6 to 6.5, is by contrast extraordinarily tough thanks to its interlocking fibrous structure: that is precisely why the Chinese made tools from it. Hardness, toughness and cleavage are three distinct properties.
Once you have estimated hardness, cross-reference it with your stone's colour and transparency in our identification by criteria tool, which will give you a shortlist of candidates. And if you have a photo, Lapidem's AI identification does the job in seconds.
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E-book · Gemmology & the gem trade
The Merchants of Light
My name is Lorys. For over ten years I have travelled the markets, the mines and the workshops of the gem world. There I learned to observe stones, to negotiate, to recognise treatments and to understand what a gem is truly worth. The Merchants of Light is a human and practical journey. You will find field knowledge and professional insight that you will not find anywhere online.
- Travel the great gem routes
- Understand the stone trade
- Negotiate with method
- Learn to read a gem
- Recognise treatments and imitations
- Use the tools of the trade
- Buy with far greater safety
- Step into the professionals' network
- Make sense of certificates