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Hard but brittle, soft but tough? What?!

You aren’t the only one who’s squinting eyes, my friend. 

There’s a famous saying in the world of gemology (it’s something along the lines of): a jade can’t scratch a diamond, but a jade can break a diamond. 

Sadly this isn’t just a pearl of wisdom. 

Often times, when we’re considering a gemstone's durability, we’re talking in the language of Mohs scale. This scale is an indicator of a gemstone’s hardness. An image of diamond so hard it’s impossible to shatter immediately comes to mind.  

But this isn’t what Mr. Mohs meant when he said diamond is the hardest mineral on earth. On top of that, a gemstone’s toughness is just as important, and toughness is a totally different thing from hardness. 

So how is a gemstone's hardness different from toughness? And what does it mean when a jeweler tells you a gemstone is hard, but brittle? 


(opposite = soft)

You might associate hardness to be a feature of strength, something which can hardly break. But in the world of gemology, hardness doesn’t mean ‘hard’ as we know it. 

Centuries ago, a German mineralogist Fredhrick Mohs scratched one gemstone against another, then saw one remained smooth, while the other left a trace of powder. Mohs scale is an assessment of a gemstone’s ability to scratch a surface. 

Diamond can scratch ruby, ruby can scratch emerald, emerald can scratch pearls. But the same thing doesn’t go the other way around. Since nothing can scratch a diamond, diamond claims the first spot for hardness (even though it’s not the toughest). 

So to jewelers, hardness isn’t about the fragility of a gemstone, but its ability to withstand scratches. And even though scratching a rock sounds implausible, fine scratches happen everyday, all the time. 

Dust particles are actually pretty hard, no matter how fine and soft they look. Those glittery specks of dust under your bed may be quartz particles, ranking 7 on the Mohs scale. Those same dust particles might be sitting on your gemstone, making tiny scratches as you slide your hand in and out of your pocket.  

In short, Mohs scale gives you a good idea about whether you should wear your gemstone everyday or not. 

Also keep in mind that Mohs scale isn’t actually linear. To save you from technical terms, even though corundum ranks 9 at Mohs scale and diamond at 10, corundum is actually 4 times softer than diamonds. The hardness of gemstones isn’t proportional to its rank, although it’s not to say that corundum is soft (it’s still hard af). But this is a topic for another time! 

How do you rate it? 

1-10 with 10 being the hardest

What it means for your jewelry wear and care: 

  • Think of 7 as the neutral number here, since quartz particles aka dust are at 7 on the Mohs scale. Consider choosing stones harder than 7 if you’re thinking of wearing them every day.  

  • Whenever you’re putting on a jacket or putting your hand on the pocket, you’re ever so slightly scratching the gemstone. Over time, scratches can build and turn your gemstone dull. 

  • Consider putting softer gemstones as side stones, instead of center stone, to minimize the visibility of fine scratches.

  • Put hard stones such as diamonds or corundums in their own box, so it doesn’t scratch smaller gemstones. 

  • Want to wear softer gemstones? Consider them for a necklace or earrings, places that get less wear and tear than your fingers. 


(opposite = brittle)

Gemstone’s tenacity means its ability to endure breakage, like getting chipped or cracked. 

This all goes back to the molecular structure of the gemstones. Think fibrous material, like a tree or a piece of meat. Cutting against the grain will be tougher than cutting alongside the grain. 

Same thing goes for gemstones.

Certain gemstones have the tendency for ‘perfect cleavage’, where atomic structures are running in parallel (like grains), which makes the bond between planes weaker. Gemstones with this tendency are more prone to breakage. 

Diamond has a perfect cleavage, so diamond easily breaks when hit from a certain angle. Jade, on the other hand, is the toughest gemstone, even though it’s only as hard as dust with Mohs scale of 6-7. That’s why you often see jade as a sculpture (like those jade bangles or jade totem animals for good luck), but not a diamond. 

When considering a gemstone’s design, think about its toughness and how you’ll protect the gemstone, especially if it’s thinly sliced or has narrow, pointy sides. Consider also how and where you’re planning to wear it. 

How do you rate it? 

Poor, fair, good, excellent, and exceptional.

What it means to your jewelry’s wear and care: 

  • Brittle stones are best secured with a bezel setting than a prong setting, especially if you’re wearing them everyday. Bezel setting generally gives the greatest protection for your ring. However, an open bezel setting sits a tad higher than your finger and is more prone to bumping into things than a lower profile setting. 

  • Think about the relationship between the setting and the gemstone’s cuts. If you’re choosing a hexagonal cut, even for a diamond, having a claw on each corner can protect it from being chipped (because remember: diamond is prone to chipping!). 

  • Choose prong setting wisely. Yes, we love how much a prong setting can let lights through, but understand the flip side as well. Consider a basket prong (low rise, but with a lot of metal securing the gemstone) or wire basket prong (higher rise, but with thinner wire support).

  • Earrings and necklaces are the ultimate safest place for brittle gemstones like pearl or moonstone. 

Now, let’s combine both factors and look at how the gemstones rank in terms of everyday wearability: 

I’d say hardness and toughness are the first two things to take into account when designing your jewelry.

Factoring these into your design can go a long way. Because when you start thinking about its care before making a purchase, your bling can keep on shining for a long time.