Gem Hardness

Posted on April 16, 2014 by Mary Hood | 0 Comments

If you’ve ever watched a minute of TV in your life, you’re probably familiar with the famous “A Diamond Is Forever” campaign. It isn’t just clever marketing—there’s some truth behind that catchy phrase. Combined with their beauty, the hardness of diamonds makes them a natural choice for investment and everyday jewelry.

All minerals vary in hardness and are measured on Moh’s scale. Hardness refers to the mineral’s resistance to being scratched. The softest mineral, talc (think eye shadow and baby powder), is one moh. At 10 mohs, a diamond is the hardest mineral and can only be scratched by another diamond. Apatite—the stunning blue-green stone pictured below—is 5 mohs. It could be scratched by harder minerals like diamond and quartz (7 mohs), but softer minerals like talc won’t scratch it.

Blue Apatite


What This Means for Selecting Gems

Despite its hardness, a diamond isn’t always a girl’s best friend. We’d miss out on so many beautiful gems if we only wore diamonds. Nonetheless, it’s important to keep hardness in mind when selecting which gems to set in which types of jewelry. Apatite, for example, would fare best in lightly used items like earrings or pedants—as opposed to jewelry that takes more abuse like rings and bracelets. Just think about how much a bracelet bumps your desk while you clack away at the keyboard! Not ideal for maintaining the beauty of softer stones.

What This Means For Caring for Your Jewelry

While a properly fitted setting is important for all types of jewelry, it’s especially critical for diamond jewelry. Diamonds are harder than gold and platinum. If your diamond is loose in its setting, it will move and act like a little saw, wearing away the surrounding metal. Eventually, the diamond could fall out.  Loose diamonds should be repaired immediately.

Gems dazzle best when they’re clean and well cared for, but if we’re not careful, we could scratch softer stones in process of cleaning them. There’s a good chance that quartz, a very common mineral, is present in dust particles—including those that land on your stone. If your stone is softer than quartz, simply wiping away the dust with a cloth could mean dragging abrasive particles against the surface of the gem. We don’t want to sandpaper our jewelry! To safely clean softer stones, run them under a warm tap (with your drain closed), and carefully dry with a lint-free cloth.


Poster from American Educational Products

Is “Hardness” the Same As “Toughness”?

Technically speaking, no. Hardness/softness refers to how easily a stone may be scratched. Toughness, however, determines how easily a stone cracks or breaks. This is determined by the mineral’s cleavage—the tendency of the stone to split along definite planes within the crystal. Toughness/brittleness may be classed as: Exceptional, Excellent, Good, Fair, or Poor.

Although diamonds are the hardest minerals, they’re not the toughest since they have cleavage in certain directions (their toughness rates as “Excellent” in some areas and “Good” in others). Sapphires and rubies (both corundum species), however, are softer than diamonds, but have no cleavage and are therefore of “Excellent” toughness.

Ask your jeweler about the most appropriate setting and cleaning method for a stone based on its hardness and toughness.

Want to learn more about gem hardness? These fun kits may be just the ticket.


Photos: Captain Tenneal via Flickr, American Educational Products,



Posted in Diamonds, gem durability, gem hardness, Informational, jewelry care, mohs hardness, Mohs scale



Leave a Reply

Comments will be approved before showing up.