Corals From Late Devonian?

[schoolaintsobad]

Here are two pictures of the same item, one so you can see the entire specimen, and a close-up of the subject of my question.

I know the fossil on the left is a type of coral, but what about the one on the right that still has the "shell" with it? Is that coral, too, and can I successfully excise the piece from its surroundings without ruining it? We have millions of these in the creek, so it's not too big of a deal if I break it.

These are from a stream bed in northcentral PA. The entire piece is about 6" tall, and the left coral is about 1/2" across. The one on the right, with the shell, is about 1.5" long. My best guess is that this is from a part of the marine Lock Haven formation (Late Devonian). Please correct me if this is not likely... I'm still learning.

Thanks.

Edited May 6, 2014 by schoolaintsobad

[Auspex]

'Tis indeed a horn coral. It looks like it might be silicified, and might come out without too much of a fight.

[schoolaintsobad]

Thanks, Auspex. I will find one that I don't like so much and give it a pry. Do you know if these are common? We have a lot of them around here.

[Pumpkinhead]

Horn corals (or solitary rugose corals) are fairly common throughout much of the Paleozoic era.

[schoolaintsobad]

Good to know. Thanks!

[Fossildude19]

That one is kind of neat, with it's own little display stand.

Regards,

[FossilDAWG]

While you can try to free the coral by dissolving the matrix in dilute acetic or hydrochloric (sold as muriatic) acid, my guess is that that will give the opposite result. It looks to me as if the specimens are calcitic, and the matrix is harder and possibly slightly dolomitic or at least shaly. I say this because the remaining shell of the coral is recessed into the rock, so it seems to be softer or more easily dissolved than the surrounding rock. Usually silicified specimens are more resistant than the rock they are embedded in, and so tend to stand out from the rock. Also structures like beekite rings are common in silicified material (though not in every case) and I see nothing like that in your specimen. I suspect the matrix is partially dolomitized due to it have a slight crystalline sparkle.

For acid etching to work, the fossil must be replaced by silica and the matrix has to be entirely or largely made of calcium carbonate (limestone) that is soluble in acetic or hydrochloric acid. I think you may find the opposite is true of your specimen.

Personally, I think the specimen looks pretty good as it is. If these corals are abundant in your creek, instead of messing up this one I'd suggest if you look some more you'll find a variety of specimens including some that are more free of the rock.

Don

[Auspex]

I agree that I rather like this specimen as-is; it makes a visually interesting display piece. In most of the coarse Devonian sandstone of that area, anything than can be dissolved has done so (not much limestone to buffer the acidic water there), as evinced by all the impressions one normally sees.

[Wrangellian]

I agree with the others - it makes a nice display piece as is. Nice example of a Devonian reef environment (maybe algae/stromatolite type layers amongst the coral/etc. pieces, can anyone confirm?)

[kwilson]

Rugose (horn) corals are quite rare in the Upper Devonian in south central NY, but there are a few thin strata where they are common. Your specimen looks a lot like Macgeea. See:

http://bingweb.binghamton.edu/~kwilson/Devonian/DevSites/Cayuta%20Creek%20Coral%20Bed/CayutaCreekCorals.htm