What is the Mohs hardness scale?

The Mohs hardness scale of 1 to 10 is used to determine a gem's hardness. 1 being the softest and 10 being the hardest.

Hardness refers to a gem's ability to resist scratches.

Don't confuse hardness with strength. A diamond is so hard, that it can only be scratched by another diamond. However, take a hammer to it and it will shatter, as it is not strong.

Lapis lazuli, on the other hand, is hard to break with a hammer but will scratch quite easily, as it is strong but not hard.

1. Talc.

2. Gypsum. Amber.

3. Calcite. Malachite.

4. Fluorite.

5. Apatite. Turquoise. Lapis lazuli.

6. Feldspar. Zircon.

7. Quartz. Aquamarine. Amethyst. Citrine.

8. Topaz. Cubic zirconia (synthetic).

9. Corundum. Ruby. Sapphire. Moissanite (synthetic).

10. Diamond.

Be aware that anything from 1 to 7 can be scratched just by removing dust with a cloth, as all dust contains trace amounts of quartz. You should first run any gem under a tap before cleaning.