The Mohs Gem Hardness Scale

The Mohs Scale, named for the German mineralogist Friedrich Mohs, is the most commmonly used scale in the jewelry industry to rank the relative hardness of gemstones.

The term “hardness” refers to the resistance of a mineral to scratching. The hardest mineral on Earth, diamond, ranks as a 10 on the Mohs.

On this site, we refer to the Mohs ranking of the hardness of a stone. This information will be helfpul in understanding the care necessary for each gemstone, and will advise you as to how resistant each stone is to nicks, cracks, and scratches.

During my twenty-five year career as a jeweler, there were many occasions when I would have to inform a customer that their sapphire, or opal, or blue topaz stone had a serious chip in it and that one more blow would probably fracture the stone in two.

This is also possible with the ultra-hard diamond -- their girdles can chip and in severe cases, a diamond can actually be cracked if struck hard enough and at just the right spot. The “cleavage planes” in a diamond (and all other natural, mined gemstones) that allow cutting and polishing are also the weak points in a stone.

Knowing the hardness of a gemstone can make a person more aware of how to treat a ring so as not to damage the stone.

MOHS SCALE OF GEMSTONE HARDNESS

• 1: Talc
• 2: Gypsum
• 2.5 Amber
• 3: Calcite, Coral
• 4: Fluorite, Malachite
• 5: Apatite, Variscite
• 5.5: Lapis Lazuli
• 5.5 - 6.5: Chrome Diopside
• 6: Amazonite, Opal, Rhodonite, Turquoise
• 6 - 6.5: Feldspar, Moonstone, Zircon
• 6.5: Hematite, Nephrite, Peridot
• 6.5 - 7: Tanzanite
• 6.5 - 7.5: Garnet
• 7: Agate, Amethyst, Carnelian, Citrine, Iolite, Kunzite, Jadeite, Onyx, Quartz, Tiger’s Eye
• 7 - 7.5 Iolite
• 7.5: Andalusite, Aquamarine, Emerald, Morganite, Tourmaline
• 8: Spinel, Topaz
• 8.5 Alexandrite, Cat’s Eye
• 9: Ruby (Corundum), Sapphire (Corundum)
• 10: Diamond