Mohs Scale of Mineral Hardness

In the early 1800s, Frederick Mohs developed a chart that compared the hardness of ten easily accessible minerals, beginning with talc (at the softest rating, 1) and working up to diamond (with a rating of 10, the hardest). The chart is known as the Mohs Scale and is still used today.

Rankings on the Mohs Scale show a comparison of hardness among the minerals. The minerals with higher numbers will scratch minerals that rest below them on the scale, but ranks don't indicate that minerals are close to each other in hardness. For instance, diamond (10) will scratch corundum (9), but is actually four times as hard.

Today's expanded rankings of minerals and other materials offers an overview of their durability as it relates to hardness.

Original Mohs Scale, from Soft to Hard

1. Talc
2. Gypsum
3. Calcite
4. Fluorite
5. Apatite
6. Feldspar
7. Quartz
8. Topaz
9. Corundum (ruby, sapphire)
10. Diamond

Relative Hardness of Other Materials

• Pearl: 2.5
• Fingernail: 2.5
• Gold: 2.5 to 3
• Coral: 3-4
• Platinum: 4 to 4.5
• A Tooth: 5
• Opal: 5.5
• Lapis: 5-6
• Turquoise: 5-6
• Glass: 6-7
• Periodot: 6.5-7]
• Garnet: 7 to 7.5
• Emerald: 7.5-8

Why Should You Care About the Mohs Scale?

Knowing how gems rank on the scale helps you care for them in way that prevents damage:

• Jewelry Storage: Sapphire scratches opal (and anything else rated below 9) and should not be stored in a location where the two can bump up against each other.

• Everyday Wear: At 2.5, pearls would suffer from the wear and tear of everyday use and should be treated with care.

• Diamonds, the hardest mineral, are a good choice for engagement rings and other jewelry that is worn continuously, and so are 9-rated ruby and sapphire.

Hardness isn't the only factor to consider when you buy a gemstone, but it's an important ingredient to help you understand durability.