It’s often said that there’s nothing harder than a diamond, and we are often asked if a diamond is used to cut another diamond (the answer is yes)… But have you ever wondered how we know this? The answer is simple – the Mohs scale of hardness.
In 1812, Friedrich Mohs – famous geologist and mineralogist created a scale of mineral hardness grading from the softest (1) to the hardest (10). The scale was created using the simple technique of one mineral’s ability to visibly scratch another.
The softest mineral that features on the scale is Talc at 1, and everyday objects of hardness such as pencil lead (1.5), finger nails (2.5) and window glass (5.5) can help you get a true value of the scale.
| Gem | Hardness |
| Diamond | 10 |
| Ruby | 9 |
| Sapphire | 9 |
| Chrysoberyl | 8.5 |
| Topaz | 8 |
| Spinel | 8 |
| Emerald | 7.5 – 8 |
| Aquamarine | 7.5 – 8 |
| Morganite | 7.5 – 8 |
| Amethyst | 7 |
| Quartz | 7 |
| Tourmaline | 7 – 7.5 |
| Citrine | 7 |
| Tanzanite | 6.5 – 7 |
| Peridot | 6.5 – 7 |
| Jasper | 6.5 – 7 |
| Tiger’s Eye | 6.5 – 7 |
| Zircon | 6.5 – 7.5 |
| Bloodstone | 6.5 – 7 |
| Onyx | 6.5 – 7 |
| Moonstone | 6 – 6.5 |
| Opal | 5.5 – 6.5 |
| Lapis Lazuli | 5 – 6 |
| Turquoise | 5 – 6 |
| Malachite | 3.5 – 4 |
| Coral | 3 – 4 |
| Pearl | 2.5 – 4.5 |
| Amber | 2 – 2.5 |
Whilst this scale is a guide to mineral hardness, it does not always factor in other elements of a gemstones structure when you are considering stones for day to day wear. Emeralds for example are well documented as having many inclusions within the stone, these can often weaken the structure and make them more susceptible to scratching and even chipping – and some styles are not suitable for everyday wear. Citrines, however, are not recommended to come into contact with heat as they can fracture.
