UPDATE! Thanks to cyberpal Angela for identifying this specimen as a styolite, i.e. a mineral!
This first pic (if you click on it) is an EXTREMELY hi-res shot, over 2k pixels wide. This one is a real oddball:
It looks almost like gypsum, but found in the Boone Limestone formation, must be ... a fossil? You tell me!
Click on photos to enlarge.
I found some sedimentary rocks with fossils in the vicinity of Devil's Den State Park near Winslow, Arkansas yesterday. The rock is more like sandstone than limestone, and it is often sandwiched between thin layers of shale. Perhaps my geologist friends can help me out here? Ed. note: this appears to be in the vicinity of the Bloyd shale formation. The Bloyd shale is primarily sandstone, secondarily shale. Its time period is middle Pennsylvanian.
The rock is quite soft and porous. It also made of rather coarse particles, and the fossils are very thin and delicate. The actual fossils of what I believe are brachiopod shells often show little detail, with the cast being much better preserved.
Here's a particularly well-preserved example of one of the small coiled shells, 1/4" in size. It appears to be the same species as the larger example appearing in the previous entry. They make up 80% of the fossils found in the rock.
I found this shell today, making a trip to southern Washington County, Arkansas. Near the community of Winslow, and Devil's Den St. Park, I followed a dirt road and found some exposed rock in a ditch.
Cracking one open, I found fossils. This was excitation for me, because there is almost 700 feet in elevation difference from Benton county. I'm talking different geological era! Big stuff, friends. Different species of fauna, etc. For a landlocked fossil enthusiast, that much of a change in elevation means traveling to a foreign country, so to speak. Ed. note: this appears to be in the vicinity of the Bloyd shale formation. The Bloyd shale is primarily sandstone, secondarily shale. Its time period is middle Pennsylvanian
Here's the shell, still in its matrix.
