Dill Posted April 6, 2016 Share Posted April 6, 2016 I've been researching this piece I found in some washed up beach rocks. I'm pretty sure it's chert. But on one side it's got a white matrix (I think that's the term) and many tiny bumps of what looks to be chert. But chert isn't bumpy right? So what could this be? Thanks for any help. Link to comment Share on other sites More sharing options...
Mediospirifer Posted April 6, 2016 Share Posted April 6, 2016 Hard to tell. Your photos are rather blurry--I'd recommend re-taking them in a stronger light. That said, this could be chert with a layer of white chalk containing quartz grains. It doesn't quite look oolitic to me (but a better photo might change my opinion). Take this with several grains of salt; I'm not an expert! Link to comment Share on other sites More sharing options...
Dill Posted April 6, 2016 Author Share Posted April 6, 2016 Hard to tell. Your photos are rather blurry--I'd recommend re-taking them in a stronger light. That said, this could be chert with a layer of white chalk containing quartz grains. It doesn't quite look oolitic to me (but a better photo might change my opinion). Take this with several grains of salt; I'm not an expert! Thank you - they might be quartz but I'm no expert either lol. Here are some other photos - hopefully more clear. Link to comment Share on other sites More sharing options...
Mediospirifer Posted April 7, 2016 Share Posted April 7, 2016 Those photos are better! The white layer isn't oolitic. The (presumably quartz) inclusions are too angular; oolites have small spherical inclusions. The layer does look like limestone conglomerate. I mentioned chalk above; that's (according to Wikipedia ) a soft form of limestone. You can probably tell chalk from limestone by poking it with a sturdy pin: if it marks more than the surface, it's likely chalk! The gray layer does look like chert or flint. I see the conchoidal break pattern typical of both rocks. Jasper, agate, and obsidian will also show that break pattern. Obsidian has a glassy luster (surface quality) while the others show a 'waxy' luster. In my (very limited!) experience with obsidian, I've never seen a color other than black. Chert, flint, jasper and agate are all very similar (cryptocrystalline quartz), and all I know about telling them apart is that a sample is considered agate if it has a significant amount of clear chalcedony in it, flint if it's associated with chalk, and jasper if it has colorful patterns with little chalcedony. So, my identification would be chert with limestone conglomerate, unless a scratch test with a metal pin (or knife) leaves a deep gouge. Then it would be flint with chalk! Enjoy it. It's a cool piece. Link to comment Share on other sites More sharing options...
Dill Posted April 10, 2016 Author Share Posted April 10, 2016 Thanks so much. I'll try scratching it. Link to comment Share on other sites More sharing options...
sTamprockcoin Posted April 19, 2016 Share Posted April 19, 2016 Just for your amusement here's 2 pics of oolitic chert from the Mines Member of the Gatesburg formation collected near State College PA by me. 1 “Beautiful is what we see. More beautiful is what we understand. Most beautiful is what we do not comprehend.” N. Steno Link to comment Share on other sites More sharing options...
Dill Posted April 26, 2016 Author Share Posted April 26, 2016 Just for your amusement here's 2 pics of oolitic chert from the Mines Member of the Gatesburg formation collected near State College PA by me. Thanks - I have a bunch I need to sit w a flintknapper & identify. All kinds. Pretty fun. Link to comment Share on other sites More sharing options...
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