Jade hardness: Mohs scale, toughness and breakage
Jade hardness is 6.5 to 7 on the Mohs scale for jadeite and 6 to 6.5 for nephrite, according to GIA. That is harder than window glass and a knife blade, at or just below quartz, and only middling for a gem. What sets jade apart is a different property, toughness: both jades are among the hardest of all gems to break.
Jade on the Mohs scale
The Mohs scale ranks materials by which one scratches which. The reference points below come from the US National Park Service, with the gem figures from GIA.
| Mohs hardness | Material |
|---|---|
| 2.5 | Fingernail |
| About 3 | Marble (a common white jade imitation) |
| 3.5 | Copper coin |
| 5.5 | Knife blade, window glass |
| 6 to 6.5 | Nephrite jade |
| 6.5 | Steel nail |
| 6.5 to 7 | Jadeite jade |
| 7 | Quartz |
| 7.5 to 8 | Emerald |
| 8 | Topaz |
| 9 | Ruby and sapphire (corundum) |
| 10 | Diamond |
Two cautions about reading this table.
The scale is a ranking, not a ruler. The steps are not evenly spaced: diamond is one number above corundum yet many times harder.
Published figures for jade also vary a little. Gem-A quotes single values of 7 for jadeite and 6.5 for nephrite, and the Wyoming State Geological Survey gives 5.5 to 6.5 for Wyoming nephrite. Jade is a rock made of many small crystals, not a single crystal, so readings depend on the specimen.
Hardness is not toughness
Gemologists split durability into three separate properties:
- Hardness is resistance to scratching and abrasion.
- Toughness is resistance to breaking and chipping.
- Stability is resistance to heat, light and chemicals.
A gem can score high on one and low on another. GIA’s own summary of jade is that it is not unusually hard for a gem, but that both types are extremely tough.
How strong is jade? GIA’s toughness figures
GIA’s article on gem durability lists toughness values for several gems. It gives them without a unit, so treat them as relative numbers on one scale and nothing more.
| Gem | GIA’s toughness figure | Mohs hardness |
|---|---|---|
| Nephrite | 225,000 | 6 to 6.5 |
| Jadeite | 120,000 | 6.5 to 7 |
| Diamond | About 5,000 to 8,000 | 10 |
| Ruby and sapphire | 600 | 9 |
On these figures nephrite, the softer jade, is the tougher one by nearly a factor of two, and either jade is far tougher than diamond, the hardest gem of all.
Emerald shows the same point from the other side. It is harder than jade, but GIA rates its toughness as only fair to good, and it is usually fractured, so it chips and breaks more readily. The two green stones are compared in full in jade vs emerald.
Why jade is so hard to break
The toughness comes from structure. Both jades are masses of tiny interlocking crystals, and in nephrite those crystals are fine, felted fibers. Gem-A calls fibrous nephrite the toughest gem. A crack cannot run straight through one crystal. It has to work its way around countless grains.
People put this to use long before anyone measured it. GIA notes that Neolithic knives and axe heads were often made of nephrite, and jade also served for projectile points and scrapers. More on the two minerals is in jadeite vs nephrite.
Does jade scratch?
Yes, though not from most everyday contact.
What should not scratch it. A steel knife blade and window glass sit at about 5.5, below both jades. A fingernail or a copper coin will do nothing.
What can scratch it. Quartz, at 7, is harder than nephrite and at least as hard as jadeite. Ordinary sand and dust are mostly quartz, so gritty dust can dull a polished surface over years. Harder gems such as topaz, sapphire and diamond can scratch jade on contact, which is a reason to store jade apart from them. GIA advises some care for exactly this reason: jade is not especially hard.
What a scratch test can and cannot prove
Dealers mention the knife test because the common white imitation, marble sold in China as “Afghan jade”, is only about 3 on the Mohs scale and scratches easily. Soft man-made imitations also pick up visible scratches in ordinary wear.
The test has two problems. It is destructive, and the same dealers do not recommend it. And it cannot confirm jade: quartzite, another common stand-in, is about 7 and resists a knife just as well. A knife that leaves no mark tells you the stone is not one of the soft imitations and nothing else. For checks that do not risk the piece, see how to tell if jade is real. They narrow things down, and a gemological laboratory report settles what a stone is.
Does jade break easily?
No. GIA says both jadeite and nephrite resist breaking and chipping exceptionally well. But tough is not unbreakable, and “is jade fragile” has a different answer for different pieces. Four things make a piece weaker.
- Existing cracks. Fractures are what make jade fail. GIA notes that fractures can strongly affect jadeite’s value, and the Wyoming survey says fine fractures or a schistose grain drastically reduce nephrite quality. Chinese dealers warn that a crack (lie, 裂) already in a bangle can lengthen at the next knock. They separate cracks from “cotton” (mian, 棉), the white cloudy inclusions natural to most jadeite, which affect looks but not strength.
- Coarse, loosely packed material. Not all jadeite is equally sturdy. In coarse, grainy grades the bonds between grains are weaker. Such material can show pits after polishing, and dealers say it is the most likely to develop internal flaws over years of wear.
- Acid treatment. Bleached and polymer-filled jade, known as type B, is weaker than untreated jade, because the acid can make the stone brittle.
- Thin sections. Toughness is a property of the material, and a slender bangle has less of that material to resist a knock than a thick one does.
How a given bangle fares when it hits a hard floor depends on the piece and the blow, and nobody can promise either outcome. What can be said is this: sound, fine-grained, untreated jade resists breaking far better than most gems, and a crack, a thin section or acid treatment takes away part of that margin. What breakage means and what to do afterward is covered in what it means when a jade bracelet breaks.
“Hard jade” and “soft jade”
Chinese has a pair of names that confuses the picture: yingyu (硬玉), “hard jade”, for jadeite and ruanyu (软玉), “soft jade”, for nephrite. Soft jade is not soft. Nephrite is only about half a Mohs step below jadeite, and it is the tougher of the two. In wear the half step matters little, since the same things scratch both.
Heat and chemicals
Stability is the third part of durability. According to GIA, jade is stable to light, but heat from a jeweler’s torch can harm it and warm acids can affect it. Warm soapy water is always safe. Ultrasonic and steam cleaners are safe only for untreated jade, which is one more reason to know whether a piece has been treated. The routine is in how to clean jade.
Frequently asked questions
How hard is jade on the Mohs scale?
Jadeite measures 6.5 to 7 and nephrite 6 to 6.5, according to GIA. That is harder than a knife blade or window glass and at or just below quartz.
Does jade break easily?
No. Both jadeite and nephrite are among the toughest gems, meaning they resist breaking and chipping exceptionally well. Jade is not unbreakable, though: a piece with an existing crack, coarse loosely packed grain or acid treatment is weaker.
Can jade be scratched?
Yes. A steel knife should not scratch it, but quartz can, and ordinary sand and dust are mostly quartz. Harder gems such as topaz, sapphire and diamond will also scratch jade.
Is jade harder than emerald?
No. Emerald is harder, at 7.5 to 8 on the Mohs scale. Jade is much tougher, so emerald chips and breaks more readily even though it is harder to scratch.
Does a scratch test prove jade is real?
No. A knife scratches soft imitations such as marble, but quartzite resists a knife as well as jade does. The test also risks damaging the piece, and only a gemological laboratory report settles what a stone is.