Piedra de las conchitas

Interesting.

Thanks Ann!!

You know, I'm not certain what the base rock is. I'm thinking a siliceous limestone or siltstone. A knife will scratch my examples but just barely so I'd say hardness in parts of the matrix at least approaches mohs 5 or 6 but seems quite variable. The Indian material varies in hardness too with some harder and some softer than the Pt. Mugu stuff but the Indian material often tends to be very porous while the California material is quite solid. LA Museum of Natural History said the material is clamshell fragments and they do have a crinoid look to them if cut in certain sections but are not crinoids. Some hunks do have Turritella ( true Turritella, not the Wyoming brackish water Goniobasis snail) type marine snails as long as three inches or so and since various gastropods are associated with clams and their shells are scattered in clamshell beds, their fragments may add to the confusion. We have coquina type stuff in Texas too but the clamshell fragments are much larger and the matrix is very hard chert but I think the Texas material is from a much older period than the Miocene California material.

The Devil's Toenails is so common in some of the Rio grande gravel beds that I use it sometimes to sharpen my saw blades. The silica rich oyster shell infused limestone comes in all kinds of colors but tan to golden brown to yellow and orange are the most common and pink the most rare. The Texas cherty coquina can be pretty colorful sometimes though the shells are not as numerous. This is the fully silica replaced clamshell stuff found in the Rio Grande gravels.....Mel



Texas limestone Coquina cab. Very polishable limestone

I'm excited to get to work with this stuff!!!

Nope, real shell fragments in the matrix. If I put some under my dissecting scope, various pieces show definite shell anatomy. You can see pieces of edges, pieces of the valves and in some cases a cross section of the entire shell. Coquina shells are usually of the genus Donax but some of the shells in the shell rock appear to have wavy edges and Donax I've seen is a very smooth shell. Maybe some real fossil expert here who knows Commiefornia fossils well can ID the shells more accurately..Mel

100% this material is marble. Highly acid reactive.

I'm still saying still harder than steel.
Takes an interesting polish. The shells and other fragments polish better than matrix.

Pix soon

Shake up, wake up fossilman too, he has been on a roll lately..

Scott, probably cuts through the suture where thee valves connect and the shell is thickest. You are seeing both valves ( both sides of the clam. And remember this is a fossil graveyard of stuff that has settled to the bottom. There are scallops cockles etc that could have shell fragments in the mix. There are also snails, gastropods, in this broken shell mix too. Probably shell fragments from lots of ocean organisms besides just clams Some of the ladder looking sections could be cuts through broken gastropod shell sections too. Also many sea worms have calcareous shells too and could be in the mix as could oysters, echinoderms like sand dollars etc. I've omitted crinoids simply because they are more scarce in that time period. Could be some there but much less likely. I've never seen any in the mix....Mel

Scott: Regarding the crinoid thing. We have a lot of crinoidal limestone ( actually more marble) in Texas near where I live. Unfortunately, most is in parks or on prvt land but I have hunted it on the Lambert ranch and have cut a lot Have never cut crinoidal material without seeing a lot of the prefect circles and disks associated with the stalks and tentacles That to me is always a good identifier....Mel