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Mohs Scale of Hardness


The Mohs hardness scale measures the relative hardness of gemstones, as determined by their scratch hardness (the resistance of a mineral when scratched with a pointed testing object.)

The diamond is the hardest natural gemstone in the world and measures a ten on the hardness scale. Gemstones measured at a one can be easily scratched with a fingernail. To learn the hardness of many popular gemstone materials, see the chart below.

Scale Hardness Material
1 Can be scratched easily with a fingernail Sulfur: 1 - 1-1/2
2 Can be scratched with fingernail Amber: 2 - 3
Ivory: 2 - 4
3 Can be scratched with coin Pearl: 3 - 4
Coral: 3 - 4
Malachite: 3-1/2 - 4
4 Can be scratched easily with a knife; cannot scratch glass Rhodochrosite: 4
5 Can be scratched with a knife; can just scratch glass Lapis Lazuli: 5 - 6
Turquoise: 5 - 6
Opal: 5-1/2 - 6-1/2
6 Can be scratched with a steel file; easily scratches window/bottle glass Moonstone: 6 - 6 1/2
Tanzanite: 6-1/2 - 7
Peridot: 6-1/2 - 7
Zircon: 6-1/2 - 7-1/2
7 Easily scratches metal, glass and softer stones Quartz, Citrine, and Amethyst: 7
Tourmaline: 7 - 7-1/2
Garnet: 7 - 7-1/2
Emerald: 7-1/2 - 8
8 Scratches quartz and softer stones Topaz: 8
Alexandrite: 8-1/2
9 Scratches topaz and softer stones Ruby: 9
Sapphire: 9
10 Scratches ruby Diamond: 10

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