victor1941
fully equipped rock polisher
Member since November 2011
Posts: 1,975
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Post by victor1941 on Feb 15, 2019 17:37:00 GMT -5
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Post by stephan on Feb 16, 2019 0:12:55 GMT -5
Ah... mow we're talking... jade. I was fortunate to be a member of the Sacramento Mineral Society when Donald Dupras (who quite literally wrote the book "California Jade") was also there. I learned a bit about that wonderful stone. But before I rhapsodize, I will give the same advice that I give for breccia, poppy jasper, dino bone and other stones you suspect might be fractured. Drop in onto concrete from about waist-high. Anything that doesn't survive that, also stood a good chance of breaking during cutting or cabbing. Now, on to jade. Nephrite is formed in subduction zones, about 3-5 miles below the crust (jadeite even deeper), and in a mixture of minerals that are about the viscosity of toothpaste and getting churned around at about 500°C. So often there is not an even mixing, resulting in a mottled appearance (more about this later). At some point for us to find it, it must come to the surface. As tough a jade is (toughness is different from hardness -- it is a measure of resistance to fracture, rather than resistance to scratching) -- tougher than diamond, in fact -- it can fracture on this journey. Sometimes it heals. Sometimes it doesn't Sometimes it heals with talc, which isn't much help in the toughness department. Now, this potential fracturing and mottled appearance can make it difficult to judge what will hold up, and what won't -- especially from a picture. You could do the drop test, or something less potentially destructive. You could run a fingernail over what may or not be a track. If it catches, the potential for trouble is higher. If it doesn't, it's no gurantee of success, but your chances are better. Now, back to the mottling. The chemical formula for nephrite is Ca2(Mg,Fe)5Si8O22(OH)2. The color is influenced by the ratio of iron to magnesium, with more iron resulting in darker green, and a lack of iron resulting in white. Nephrite is also fibrous, so what appears to be cracks, often isn't, or will still hold up. All that to say, I've done a fair number of jade cabs, and only one has broken on me, if I exclude the materail from my early days, where I'm pretty sure that I was sold serpentine instead. Now, I've only cabbed, never tumbled or vibed, so I can't give much advice there. I have heard people say they use their "obsidian recipe," which is consistent with my cabbing experience -- I use the same technique for getting a good shine for both obsidian and jade. I hope any of this helps.
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victor1941
fully equipped rock polisher
Member since November 2011
Posts: 1,975
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Post by victor1941 on Feb 16, 2019 12:03:47 GMT -5
Stephan, I did't have a problem dropping to see what breaks and what stays intact and I dropped the 4" x 6" slab. It fractured and sounded like glass and broke into both large and small pieces. Some breaks were along the marked lines but most are just randomly spaced. Some of the Stone Canyon jasper shows the same soft lines or areas and will definitely break in the vibe but almost all of these marked areas stayed intact. Working around bad areas is not a concern for me since I always want the best piece and not a mediocre product. I have done several pieces of obsidian mixed into a regular tumble with good results. Thanks for your input.
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Post by greig on Feb 20, 2019 14:17:44 GMT -5
The drop test would make a good video! ;-)
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Sabre52
Cave Dweller
Me and my gal, Rosie
Member since August 2005
Posts: 20,455
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Post by Sabre52 on Feb 21, 2019 19:52:49 GMT -5
I've cut quite a few jade cabs and had some advice from experts. Jade is very variable in texture and even in hardness in some varieties. Onion skinning is pretty common as is undercutting where there are inclusions of manganese or magnetite. Expert told me most of this problem can be solved by sanding with very worn belts or wheels with a very light touch. Fresh diamond wheels will gouge the heck out of the softer parts of jade. Again though, this varies from variety to variety. Some jades are very homogeneous in texture and hardness and some are extremely problematic with lots of softer zones. Cabbing them is a trial and error process. Heck, as Stephan has said, more than a few folks sell harder serpentine types as jade and some of then actually work up better than real nephrite.
Far as tumbling jade goes, most forms I've tried do not tumble worth a darn. I have seen good results with the jade from Mariposa county, CA. I had high hopes for some nice looking Wyoming nephrite I tried but in the fine grind it came out with a lumpy pebbly texture from soft spots and onionskinning. Waste of a tumbler full of jade that would have made nice cabs. Again it seems to take a lot of trial and error and a long learning curve.....Mel
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Post by parfive on Feb 21, 2019 20:29:59 GMT -5
Evidently, that curve hasn’t improved much in the last few thousand years. : )
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victor1941
fully equipped rock polisher
Member since November 2011
Posts: 1,975
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Post by victor1941 on Feb 21, 2019 22:26:33 GMT -5
Thanks for the heads up advice.
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Post by stephan on Feb 21, 2019 22:51:23 GMT -5
I've cut quite a few jade cabs and had some advice from experts. Jade is very variable in texture and even in hardness in some varieties. Onion skinning is pretty common as is undercutting where there are inclusions of manganese or magnetite. Expert told me most of this problem can be solved by sanding with very worn belts or wheels with a very light touch. Fresh diamond wheels will gouge the heck out of the softer parts of jade. Again though, this varies from variety to variety. Some jades are very homogeneous in texture and hardness and some are extremely problematic with lots of softer zones. Cabbing them is a trial and error process. Heck, as Stephan has said, more than a few folks sell harder serpentine types as jade and some of then actually work up better than real nephrite. Far as tumbling jade goes, most forms I've tried do not tumble worth a darn. I have seen good results with the jade from Mariposa county, CA. I had high hopes for some nice looking Wyoming nephrite I tried but in the fine grind it came out with a lumpy pebbly texture from soft spots and onionskinning. Waste of a tumbler full of jade that would have made nice cabs. Again it seems to take a lot of trial and error and a long learning curve.....Mel Ah ha! My wheels are worn as heck, so I guess I should focus on jade until I can afford new ones. Silver lining. As far as the jade/serpentine thing goes, I’m willing to cut A LITTLE bit of slack if it seems like it’s in the transitional zone. I still fell it’s dishonest if the sell it as jade, but it’s not quite as egregious. Serpentine and Nephrite ARE related. Both are formed from a mixture of pillow basalt and ocean floor muck (such as radiolarians). The mixture is subducted, and the main difference is how deep it goes. If I remember correctly, serpentine is formed at a depth of 1-3 miles; nephrite at 3-5 miles and jadeite at greater than 5. I’ll have to verify those numbers at some point. In any case, the depth changes the actual chemical composition as well as the crystal structure. The deeper it goes, the harder, tougher and more homogeneous it gets. The homogeneity does not necessarily apply to the color. Just the hardness and toughness.
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