Jade Hardness

[sunflowers]

I was watching an antique show on TV and heard an appraiser say that Jade was harder than steel. If you use a steel piece to try to scratch jade, the jade will not get any scratch mark.

I always thought that steel would be much harder than jade. I know that jade can break easily. If you drop a jade bracelet, I think it will break. Maybe jade is harder than steel, but more brittle?

Can anybody help on this topic?

 

[DiamondExpert]

It''s true that most steel, say in a knife blade, is slightly less hard (~5 to 6 for high carbon) than jade (nephrite-6-6.5/jadeite-6.5-7). Hardness is defined a resistance to scratching, and toughness resistance to breaking/smashing.

Jadeite is very tough, however, due to its interlaced, micro-polycrystalline form - the toughest of all gem material. It is not easily smashed.

Diamond has 4 cleavage planes due to its crystalline structure, but jadeite/nephrite has none except on a microcrystalline scale. Yikes - just think of the countless diamonds, which in centuries past were needlessly shattered because they were thought to be impervious to breakage and thus tested by smashing with a hammer!!

Cutting jadeite/nephrite is done using saws charged with diamond, corundum or carborundum (silicon carbide) Carving is done with pastes of quartz, garnet, corundum, diamond dust, and polishing with any number of abrasives including plain bamboo.

 

[Richard M.]

Date: 8/22/2006 12:30:10 AM
Author:sunflowers
I always thought that steel would be much harder than jade. I know that jade can break easily. If you drop a jade bracelet, I think it will break. Maybe jade is harder than steel, but more brittle?

Back to some basics, sunflowers. On the hardness scale devised by mineralogist Friedrich Mohs, gems of 6 hardness can be scratched with a steel file. Gems of 5 hardness can be scratched with a knife, which is a softer form of steel than specially hardened files.

There are two minerals called jade: nephrite and jadeite. Jadeite varies in hardness between 6.5 and 7: much harder than steel. Nephrite varies between 6 and 6.5: mostly harder than steel but some softer pieces might be scratched by hardened tool steel. So what the man said on TV is essentially true: jade is harder than steel, as are most of the minerals used as gems: agate, chalcedony of 7 or so hardness and on up the scale to diamond at 10.

Brittleness is also defined as toughness. It happens that both jades are the toughest minerals around and are extremely resistant to breakage. That''s because they are nade of interlocking fibers that are really strong. Stone age people quickly learned about that property of jade and it became known as the "axe stone." That strength combined with its lovely colors led many early cultures to revere jade. This early Chinese ear ornament is an example. Where it was available it became the preferred stone for carving into statues and icons of spiritual significance.

Richard M.

 

[sunflowers]

Thank you, diamondexpert.

I checked out the link at the end of your post and saw at your website that you are a Ph.D. and a G.G..

I was curious about what your Ph.D. degree was in. Would you mind to share?

 

[DiamondExpert]

chemistry/neurochemistry