What's that pattern ?

[fifbrindacier]

Hi everybody.

I found that piece in a pile of rejection from an ancient quarry, among inocerams, and traces of ammonites.

I really have no idea of what it can be : ammonite chambers, sponge, algae... ?

It is about 3,2 cm long and 1,7 cm wide.

[fifbrindacier]

[caterpillar]

Certainly a part of sponge

[Spongy Joe]

Certainly not a part of a sponge!

 

I think this is actually just colouring - possibly surficial (an oil drop) or some unweathered, carbon-rich patch in the rock. Notice that the rock has lumps in, throughout. The white bits in the 'fossil' are just the unstained lumps, with a darker stain or matrix around them.

Ideally, you want cut it in half to see what's really going on.

[fifbrindacier]

I cut it and here is how it shows :

[fifbrindacier]

[ynot]

Looks like a mineral filled crack in the rock.

[Plax]

count me in the sponge camp.

[Spongy Joe]

Still not a sponge!

 

A bit odd, nonetheless, and obviously not just a surface stain. Is the rock even sedimentary? I can't help wondering if this is an igneous intrusion - the tip of an intermediate dyke, for example, with chunks of the felsic surroundings collapsed into it. It does happen on this scale.

Got any acid to test whether it's limestone?

 

If it is limestone, then I'm wondering at either a mineralised fault zone (as ynot says), or some peculiar trace fossil... but wouldn't swear to anything at the moment!

[fifbrindacier]

It fizzes a lot with  vinegar. In the geologic description of the place it is said marly limestone.

[supertramp]

looks like  some metal sulfides in a (brecciated?) limestone

 

ciao

[fifbrindacier]

There's no magmatic rock around, so we can forget the felsic rock.

[Plax]

I'm still in the sponge camp. We get fairly amorphous sponges here in our Eocene Castle Hayne Formation. Some of the cherty ones have "eyes" that look grossly similar to this specimen. Have included pics of a broken surface and unbroken.

[abyssunder]

Maybe the dark-grey mineral is Pyrolusite , which might look like a sponge.

link

[FossilSniper]

12 hours ago, ynot said:

Looks like a mineral filled crack in the rock.

I agree. It does not seem fossiliferous.

[fifbrindacier]

I found this on the net that, in some ways, looks like this pattern : https://english.fossiel.net/id_system/fossil_id_search.php?cat=32&pagina=7 Pleurochorium schulzei, note i'm not meaning i think it is one.

[doushantuo]

I'm with Supertramp on this one,perhaps dolomite cement forming the pattern