Deleted
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Post by Deleted on May 20, 2022 12:06:45 GMT -5
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Fossilman
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Post by Fossilman on May 20, 2022 12:44:17 GMT -5
Looks like a bit of both...
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Post by Peruano on May 20, 2022 13:08:47 GMT -5
I agree that a couple of pieces look something like wood, but you are in a classic place of find cherts and my money will stay on that horse. Pretty stuff, polish away.
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Post by Bob on Jun 15, 2022 22:00:09 GMT -5
I see thousands of pieces of chert like that near me yearly. It's super common along Oklahoma/Arkansas border and in Missouri some too though more brown. Like opal, crystal quartz, etc. chert also is at times the replacement material that mineralizes organic matter. I'm tumbling a lot of chert petrified wood now.
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Post by Bob on Jun 15, 2022 23:19:16 GMT -5
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Post by rmf on Jun 16, 2022 2:52:16 GMT -5
Yep Chert
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Post by Deleted on Jun 16, 2022 9:38:54 GMT -5
BobThanks Bob! I agree chert is one of my favorites and an underdog in my opinion. That’s a nice batch! I really like the white with pink in them.
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Post by Deleted on Jun 16, 2022 9:40:30 GMT -5
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Post by Bob on Jun 16, 2022 10:38:19 GMT -5
Bob Thanks Bob! I agree chert is one of my favorites and an underdog in my opinion. That’s a nice batch! I really like the white with pink in them. That's vanport chert from Ohio. Some of it has greens and is gorgeous. It's brittle and not easy to tumble.
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Post by Deleted on Jun 16, 2022 11:37:44 GMT -5
Bob Thanks Bob! I agree chert is one of my favorites and an underdog in my opinion. That’s a nice batch! I really like the white with pink in them. That's vanport chert from Ohio. Some of it has greens and is gorgeous. It's brittle and not easy to tumble. It does look different from the chert we have up here in Illinois. It’s really pretty. I love how chert can be so varied in color and patterns. I first started loving chert before I knew what it was, even before really getting into rocks, because of the texture and break pattern of rough chert. I have a few pieces that I won’t tumble b/c I like the feel of it rough.
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Post by Bob on Jun 16, 2022 14:28:28 GMT -5
Did you find that piece you photo'd near where you are in Utica? I don't think I've ever seen chert that light in color N of St. Louis, MO and I see Utica is a long ways further N.
Vanport (also called Flint Ridge) chert and western Oklahomas chert are in my opinion two of the most beautiful rocks that occur in the US for tumbling. Cherts and jaspers are forms of chalcedony which have a granular rather than a fibrous internal crystalline structure as in agates. Both are opaque, and jaspers are typically split off from cherts for having up to 20% foreign material, much of which is responsible for the wide variety and amazing colors of the jaspers. Some technically classify all jaspers as merely a form of chert though. Cherts in this country are commonly called flints, but a careful reading reveals that we should be using flint only for a form of chert that occurs in chalk or marly limestone formations. I can't remember if that happens on this continent, but it does happen in the UK and in Europe. "Flint" knappers very much dislike that they are actually knapping chert and so the terms more or less are interchangeable around here.
There are plenty of cherts that have unique names that don't reveal they are chert, such as novaculite and mookaite.
The yellow on the chert you found is often just iron staining that is barely past the surface. At other times, it's part of the rock and goes deep. There are places near me where you can't get to almost any stream w/o walking on large areas of chert that crunch beneath your feet. There are parts of NW Ark that you can barely even dig in a yard more than a few inches deep w/o encountering chert gravel.
A couple of tips. Learn what Hertzian cones and conchoidal fractures are on rocks. If you see those when you are wandering, the chert is very high quality. Also, if you click one piece against another piece, the higher the pitch of the sound the higher the quality and less internal fractures. By quality I mean best chances for a finished, shiny, sound tumble. Most "stream chert" of like you have has no conchoidal fractures. Most has straight and flat fractures. Don't pick up those pieces unless you see you can cleave off and be left with a good solid piece. The first few weeks of coarse grind will sometimes cause broken corners and new fractures, but that's okay, just be patient and keep going with the good pieces.
Chert is often used in parking lots and such but of low quality. But sometimes it is very high quality. In some streams, I have found chert petrified stumps that were too large to carry. That pile I photographed has pet wood pieces scattered here and there in it. Some pieces of what we call "banded chert" will have one or more bands that are porous and you can find out by licking and watching what happens with your saliva. If it soaks in quickly in those bands, throw it back.
Obviously, I'm a chert net!
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Deleted
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Post by Deleted on Jun 16, 2022 15:51:52 GMT -5
BobYes Bob, that is all from a local park. Wow, you really know your chert! Thanks for the knowledge! here is a link to a batch of chert I ran through a few weeks ago. forum.rocktumblinghobby.com/thread/99202/2nd-batch I’ll look up those terms you listed. Thanks again!
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Post by Bob on Jun 17, 2022 11:05:42 GMT -5
Those are nice! One piece looks a bit like Mary Ellen jasper. But that is far from its source in northern MN, so doubtful.
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victor1941
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Post by victor1941 on Jun 18, 2022 10:55:21 GMT -5
Bob, your hertzian cone fracture was extremely interesting as a means to measure quality in chert. Are the fractures that we see in glass quite often hertzian cones and the same on worked chert where the initial strike might occur?
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Post by Bob on Jun 19, 2022 17:24:16 GMT -5
I think yes, but am uncertain.
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Post by Bob on Jun 20, 2022 9:35:55 GMT -5
Jun 16, 2022 15:51:52 GMT -5 ashley said: Bob Yes Bob, that is all from a local park. Wow, you really know your chert! Thanks for the knowledge! here is a link to a batch of chert I ran through a few weeks ago. forum.rocktumblinghobby.com/thread/99202/2nd-batch I’ll look up those terms you listed. Thanks again! Those are beautiful! Here's an example of a piece of chert PW. It's been in rough grind off and on for over a year to try to get all the edge fractures out. I've probably decreased its mass by over 50%.
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Post by Deleted on Jun 20, 2022 22:43:32 GMT -5
BobThat’s a pretty one! Nice size too!
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