New Members kasci216 Posted November 5, 2016 New Members Share Posted November 5, 2016 Hey all, I'm confused by the oval or egg-shaped structures in the middle of this rock. There are several crinoid stems and fragments all through the rock. I picked this up in a creek bed in Fayetteville, Arkansas. Any help would be appreciated! Link to comment Share on other sites More sharing options...
BobWill Posted November 5, 2016 Share Posted November 5, 2016 Hello kasci. Welcome to the forum. I think all of the views without any replies yet suggests that we all are confused by your find. It looks like the oval shapes are crystalized and it might help to know a few things I can't tell from the photo. Are they crystalized and if so is it calcite or something harder? A hardness test might help. Just find the list of what will scratch what online. Where was this found and what age or formation was it in? Are the other bits with a similar color made up of the same material as the ovals? They certainly aren't eggs despite the shape and are probably just geologic in origin given the other inclusions. It might also help to get views of the rock from other angles. Someone else may see something more but I'm afraid that's all I can offer. Thanks for posting it, I certainly would have taken it home for a closer look too. 1 Link to comment Share on other sites More sharing options...
doushantuo Posted November 5, 2016 Share Posted November 5, 2016 Welcome to the forum from me. Bob is right,intriguing piece and nice find. Calcite diagenesis(the whole of the mineralogical transformations a piece of rock can go through) CAN lead to xenomorphism of echinoderm ossicles. And why am i thinking this? Because of the presence of at least one discoidal fragment that looks like a crinoid ossicle,AND the fact that you say the rock contains a lot of crinoids. A crinoid ossicle is,crystallographically speaking,a single giant calcite crystal. This makes encrustation with radaxial cement easier. Uintacrinus is a famous example 1 Link to comment Share on other sites More sharing options...
ynot Posted November 5, 2016 Share Posted November 5, 2016 It looks like a breccia. One rock broke (was eroded to the rounded shapes) and other minerals filled the voids. Tony 1 Link to comment Share on other sites More sharing options...
fossiling Posted November 5, 2016 Share Posted November 5, 2016 can you show us the crinoid stems? would love to see them! Keep looking! They're everywhere! Link to comment Share on other sites More sharing options...
tmaier Posted November 5, 2016 Share Posted November 5, 2016 Yeah, you could call this brecca or conglomerate. The grey stones are from on formation, they became broken up, and then re-mixed into this new substrate. The oval objects are likely to be internal molds of bivalves or brachiopods, in my opinion. And one reason that you didn't get replies is that SOME of us go to bed at a civilized hour. Link to comment Share on other sites More sharing options...
minnbuckeye Posted November 5, 2016 Share Posted November 5, 2016 6 hours ago, fossiling said: can you show us the crinoid stems? would love to see them! There is a nice crinoid cross section in the lower right aspect of the specimen. Link to comment Share on other sites More sharing options...
New Members kasci216 Posted November 5, 2016 Author New Members Share Posted November 5, 2016 Thank you all for responding! This forum is absolutely fascinating! All of the bits and pieces seem to be the same material, I will attempt a hardness test later, as I'm still trying to figure out what I'm doing The greenish hue is due to the algae crust I've attempted to clean off of the rock. I found it in a creek that is in south Fayetteville unfortunately I'm not learned enough to say much more about the age or formation Interestingly I found a nearby rock with the exact same oval shape in it. I'm still working to clean the algae so I can see the back of the rock better. I'll post a different angle and a picture of the back side that I am still trying to clean. Link to comment Share on other sites More sharing options...
New Members kasci216 Posted November 5, 2016 Author New Members Share Posted November 5, 2016 Here is the backside with an oval shape I'm still working to clean. Link to comment Share on other sites More sharing options...
New Members kasci216 Posted November 5, 2016 Author New Members Share Posted November 5, 2016 And here is the same oval in a nearby rock I found. Link to comment Share on other sites More sharing options...
TqB Posted November 5, 2016 Share Posted November 5, 2016 I think that most if not all of the fragments are crinoid. There seems to be a central perforation on the large ovals as well which suggests they're tangential stem sections - particularly clear in the top one. They may have been obscured by calcite overgrowth. (Edit: also showing in your latest photo.) 1 Tarquin Link to comment Share on other sites More sharing options...
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