Actual Shell Material?

[grommit]

I know this is supposed to be rare, but it is what it looks like to me.

Found in Cedar Hill, TX, in limestone/chalk.

The second shot is oblique.

The third is something else entirely. This piece of chalk has lots of little hard things. Any reason not to bust it open?

[kauffy]

Hey Grommit.

Finding original shell preservation on fossil shells is not that rare, often a shell starts off as calcium carbonate and after fossilisation is still calcium carbonate. and sometimes, although replaced by a different mineral, the "shell" is still preserved. It appears you have found a section of an Inocerimus bivalve...these shells are very common in cretaceous seas. I found a lot of ones with very similar shell preservation in Pueblo CO. I found though, finding a whole one is hard as the shell tended to break apart and splinter.

Im not sure what the other thing you have is, the larger colum looking one appears to be a crinoid stem? take a picture of the top end of it.....

hope this helps

Kauffy

[Shuko]

Hey Grommit.

Finding original shell preservation on fossil shells is not that rare, often a shell starts off as calcium carbonate and after fossilisation is still calcium carbonate. and sometimes, although replaced by a different mineral, the "shell" is still preserved. It appears you have found a section of an Inocerimus bivalve...these shells are very common in cretaceous seas. I found a lot of ones with very similar shell preservation in Pueblo CO. I found though, finding a whole one is hard as the shell tended to break apart and splinter.

Im not sure what the other thing you have is, the larger colum looking one appears to be a crinoid stem? take a picture of the top end of it.....

hope this helps

Kauffy

It also looks to me like some kind of mineral crystal... the fact that it comes from chalk makes me suggest calcite. I don't remember seeing a crystal formation like that, but Calcite has well over 300 crystal formations, so I wouldn't rule it out.

[Guest solius symbiosus]

Most sea critters secrete aragonite, a polymorph of calcite. Aragonite has different crystal structure(orthorhombic) than calcite(trigonal), but contains the same elements. During diagenesis(and over time), the aragonite reverts to the more stable form of calcium carbonate, ie, calcite.

There are some critters that secrete calcite. I have found Ord. molluscs with origonal material.

Too, I'm thinking all the echinoderms secrete calcite, but I could be wrong on that.

[kauffy]

ahh yes ^^ hahaha i didnt rule anything out i was just stating that a shell can stay calcium carbonate after mineralisation! i have no idea what excactly the mineral composition of that shell is, i never new when i was picking them up, hmmm anyway i have some pictures of the stuff i picked up, perhaps you can compare these to your specimin......they are just lots of fragments of the Inocerimus bivalves, in a chalky limestone....

[LanceH]

If you venture a little more west where the chalk (Austin) ends and gives way to the dark blue-gray clay (Eagleford) underneath it you might find shark teeth. In fact the contact between these two formations is a fossil hot zone.

I know this is supposed to be rare, but it is what it looks like to me.

Found in Cedar Hill, TX, in limestone/chalk.

The second shot is oblique.

[Guest solius symbiosus]

ahh yes ^^ hahaha i didnt rule anything out i was just stating that a shell can stay calcium carbonate after mineralisation! i have no idea what excactly the mineral composition of that shell is, i never new when i was picking them up, hmmm anyway i have some pictures of the stuff i picked up, perhaps you can compare these to your specimin......they are just lots of fragments of the Inocerimus bivalves, in a chalky limestone....

I've only seen Paleozoic stuff, but the ones I have seen were exfoliating ... at least to some degree, but it was obvious that it was original material.