JR8675309
freely admits to licking rocks
Member since August 2019
Posts: 751
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Post by JR8675309 on Sept 28, 2021 15:10:28 GMT -5
Found on Oregon (southern) coast. Mohs: scratches with knife but not penny. I see a conchoidal fracture or two. Anyone know if this is serpentine or?? While in Jedidiah S.P. I did find serpentine that I could carve with a knife. This is harder. I have more to ID but will post those Later possibly in a separate thread. Thanks for looking.
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Post by rmf on Sept 28, 2021 15:30:45 GMT -5
In the last image you show a clear conchoidal fracture. So it is jasper not serpentine. It should be hardness of 7 (quartz) not 5-6 (serpentine).
Try to scratch with steel file. Serpentine will scratch green jasper will not.
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rewdownunder
spending too much on rocks
Member since March 2012
Posts: 357
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Post by rewdownunder on Sept 28, 2021 18:42:11 GMT -5
Not sure on that one. Does it seem kind of heavy? Higher specific gravity? I also see several flat smooth surfaces in addition to the conchoidal fracture. Could these be cleavage planes? Great clear photos. Can you shine a light thru a thin edge or corner. It may be translucent
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Post by amygdule on Sept 29, 2021 10:56:37 GMT -5
That looks like one of those typical Green and Yellow jasper nodules that has been broken in half. It's not unusual to find them laying around after they weather out of the Basalt.
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JR8675309
freely admits to licking rocks
Member since August 2019
Posts: 751
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Post by JR8675309 on Sept 29, 2021 11:31:22 GMT -5
It scratches with a knife leading me to believe it's a serpentine derivative. Based on where I was, I wonder if it was antigorite.
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rewdownunder
spending too much on rocks
Member since March 2012
Posts: 357
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Post by rewdownunder on Sept 29, 2021 11:57:36 GMT -5
The hardness rules out jasper. You may be on the right track with antigorite given the geologic setting it would be posable or something related in the serpentine group. Not sure how to confirm it.
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Post by amygdule on Sept 29, 2021 12:13:35 GMT -5
The exterior of the nodules are usually soft and punky There is a lot of variation in hardness and silicification Some are mossy or solid Chalcedony inside
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rewdownunder
spending too much on rocks
Member since March 2012
Posts: 357
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Post by rewdownunder on Sept 29, 2021 13:16:20 GMT -5
The first photo has several flat surfaces that look like cleavage planes to me that is why I was leaning away from chalcedony or some kind of jasper. If you can rub it hard on a piece of glass and some of the grains leave a scratch then it might be a nodule of soft chalcedony. When something is made up of grains or several different minerals you can often get false hardness test trying to scratch it with a knife. Example: most sandstone can be scratched with a knife but the quartz grains themselves will leave a scratch on glass. Mineral ID from photos is never fun or perfect. Love to see what it looks like if you hit it with a rock hammer to get a fresh surface. It is a pretty green rock.
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Post by stephan on Sept 30, 2021 0:37:12 GMT -5
Agree with it not being serpentine, if it has conchoidal fracture. The perfect cleavage planes can occur with chalcedony, if the conditions are right. I also see no evidence of a fibrous composition or fracture.
As for hardness of serpentine, it varies. Remember, there is a continuum of serpentine -> nephrite -> jadeite, depending on the depth of subduction. Sometimes it can be frustratingly variable within a piece that is on the cusp.
Bowenite is gemmy serpentine that resembles jade (and is often used as a simulant), and can vary from 4-6 in hardness in the same piece.
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rewdownunder
spending too much on rocks
Member since March 2012
Posts: 357
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Post by rewdownunder on Sept 30, 2021 9:25:11 GMT -5
This has nothing to do with the ID but Nephrite and Jadeite are two different minerals. Nephrite is an amphibole and Jadeite is a pyroxene. They are not related other than they are both found as green fine grain rocks. Without a thin section and microscope you can not tell the difference. Chalcedony is a cryptocrystalline form of quartz as it has no crystal structure it can not have cleavage by definition but that is not to say it can not break in flat surfaces. I am going to stick with "pretty green rock" I do not know of any nondestructive tests that tell us a lot more without having the rock in my hand.
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JR8675309
freely admits to licking rocks
Member since August 2019
Posts: 751
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Post by JR8675309 on Sept 30, 2021 11:09:26 GMT -5
Interesting. I note that it also scratches glass but is scratched by a steel file... could vary based upon area of rock I suppose.
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rewdownunder
spending too much on rocks
Member since March 2012
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Post by rewdownunder on Sept 30, 2021 11:28:55 GMT -5
Chert it is. Antigorite or serpentine will not scratch glass
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JR8675309
freely admits to licking rocks
Member since August 2019
Posts: 751
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Post by JR8675309 on Sept 30, 2021 11:55:59 GMT -5
Pretty, pretty chert. Who knew green cherry existed...
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Post by amygdule on Sept 30, 2021 13:54:08 GMT -5
Some Green rocks from the Tumbler
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Post by amygdule on Sept 30, 2021 14:55:42 GMT -5
Some more Green Rocks
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JR8675309
freely admits to licking rocks
Member since August 2019
Posts: 751
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Post by JR8675309 on Sept 30, 2021 16:26:32 GMT -5
Pretty rocks!
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Post by stephan on Sept 30, 2021 22:38:34 GMT -5
This has nothing to do with the ID but Nephrite and Jadeite are two different minerals. Nephrite is an amphibole and Jadeite is a pyroxene. They are not related other than they are both found as green fine grain rocks. Without a thin section and microscope you can not tell the difference. Chalcedony is a cryptocrystalline form of quartz as it has no crystal structure it can not have cleavage by definition but that is not to say it can not break in flat surfaces. I am going to stick with "pretty green rock" I do not know of any nondestructive tests that tell us a lot more without having the rock in my hand. Actually, serpentine, nephrite and jadeite are very much related. The depth of subduction changes the chemical make-up. I got this information first-hand from two geologists. One (Donald Dupras) worked for USGS and literally wrote the book on California jade. The other (Eldridge Moores, now deceased) taught geology for UC Davis and wrote multiple books on California geology. The first was a member of our rock club, the second led educational outings throughout California. Both were respected experts in their fields
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JR8675309
freely admits to licking rocks
Member since August 2019
Posts: 751
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Post by JR8675309 on Oct 1, 2021 14:08:44 GMT -5
Some more Green Rocks I love green petwood and I love green rocks . The one below is from crook county.
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JR8675309
freely admits to licking rocks
Member since August 2019
Posts: 751
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Post by JR8675309 on Oct 1, 2021 14:09:37 GMT -5
This has nothing to do with the ID but Nephrite and Jadeite are two different minerals. Nephrite is an amphibole and Jadeite is a pyroxene. They are not related other than they are both found as green fine grain rocks. Without a thin section and microscope you can not tell the difference. Chalcedony is a cryptocrystalline form of quartz as it has no crystal structure it can not have cleavage by definition but that is not to say it can not break in flat surfaces. I am going to stick with "pretty green rock" I do not know of any nondestructive tests that tell us a lot more without having the rock in my hand. Actually, serpentine, nephrite and jadeite are very much related. The depth of subduction changes the chemical make-up. I got this information first-hand from two geologists. One (Donald Dupras) worked for USGS and literally wrote the book on California jade. The other (Eldridge Moores, now deceased) taught geology for UC Davis and wrote multiple books on California geology. The first was a member of our rock club, the second led educational outings throughout California. Both were respected experts in their fields That's the way I understand it at well (the part About depth of serpentine in subduction zones).
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Post by amygdule on Oct 1, 2021 14:38:26 GMT -5
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