ID help please

[Jba]

My son found this on the beach of Lake Superior in northern Minnesota. Sorry I don’t have a more accurate way to measure. Any ideas? Thank you!

Edited May 27, 2019 by Jba

[Tidgy's Dad]

Not sure how big that coin is, but the specimen looks like an eroded fracture mark on limestone to me. 

[Jba]

Thank you for your response.

Coin is about 1 inch/2.4 cm. I think the type of rock is basalt. That is very common around this area. 

[Fossildude19]

I agree, this is a weathered/worn breakage feature, not a fossil.

[Jba]

Thank you everyone! 

[NCSTer]

Don't know if they're found in your area or not, but it looks like a brachiopod mold to me.

[Mark Kmiecik]

Doesn't look like a fracture to me -- a bit far from the edge, but it's probably too worn to ID properly anyway.

[hemipristis]

1 hour ago, Mark Kmiecik said:

Doesn't look like a fracture to me -- a bit far from the edge, but it's probably too worn to ID properly anyway.

 

6 hours ago, NCSTer said:

Don't know if they're found in your area or not, but it looks like a brachiopod mold to me.

 

I concur,  Appears to be an impression a brachiopod (Orthid?).  I can even convince myself that I see muscle scars.  

 

The rock itself is reminiscent of a partially-recrystallized sandstone, or possible limestone, hence the coarse texture. Just for grins add some vinegar to a fresh break and see if it fizzles.

 

As for whether brachiopods "come from that area", Minnesota contains glacial till and erratics from points North, NE and NW, so Paleozoic fossils are very possible, even probable.

[Fossildude19]

8 hours ago, NCSTer said:

Don't know if they're found in your area or not, but it looks like a brachiopod mold to me.

 

3 hours ago, Mark Kmiecik said:

Doesn't look like a fracture to me -- a bit far from the edge, but it's probably too worn to ID properly anyway.

 

1 hour ago, hemipristis said:

 

 

I concur,  Appears to be an impression a brachiopod (Orthid?).  I can even convince myself that I see muscle scars.  

 

The rock itself is reminiscent of a partially-recrystallized sandstone, or possible limestone, hence the coarse texture. Just for grins add some vinegar to a fresh break and see if it fizzles.

 

As for whether brachiopods "come from that area", Minnesota contains glacial till and erratics from points North, NE and NW, so Paleozoic fossils are very possible, even probable.

 

I'm just not seeing any kind of detail or feature that points towards a brachiopod ID. 

I have seen this type of erosion on conchoidal-like chips out of certain sedimentary and igneous rocks. 

If I have to work to convince myself of seeing something, then it probably isn't actually there.  

The shape doesn't really look brachiopod-ish to me.  

 

 

 

 

I have seen odd lumps sheer off of rocks, so not being near an edge is not a deal breaker for me. 

Indeed, glacial erosion is unpredictable and often unusual. 

Regardless, even if it is  was a brachiopod,  (which I am not convinced of)   it is so worn as to not be identifiable. 

[hemipristis]

37 minutes ago, Fossildude19 said:

 

 

 

I'm just not seeing any kind of detail or feature that points towards a brachiopod ID. 

I have seen this type of erosion on conchoidal-like chips out of certain sedimentary and igneous rocks. 

If I have to work to convince myself of seeing something, then it probably isn't actually there.  

The shape doesn't really look brachiopod-ish to me.  

 

I have seen odd lumps sheer off of rocks, so not being near an edge is not a deal breaker for me. 

Indeed, glacial erosion is unpredictable and often unusual. 

Regardless, even if it is  was a brachiopod,  (which I am not convinced of)   it is so worn as to not be identifiable. 

 

The fan-shape with the hinge at the top?  What is radiating gfrom the central point therein could be remnant texture or dendrites, but I've not seen them fan out before.   

 

Note that all through this I said maybe, If it is biological, its been highly altered/recystallized and eroded.  But We shall have to agree to disagree on this one.

[Kane]

I would expect more regularity in the spacing of the ribs to declare this one brachiopod. From this image, the "ribs" do not seem to line up to the hinge, but appear to "wander" in a slightly erratic way, terminating at different points, thinning and thickening more like branches than ribs. 

 

I've processed the image as a black and white with noise reduction and boosted edges to show the features more clearly. Note how one of the "ribs" extends from the hinge at a strange, curved angle, while two other "ribs" seem to intersect with it rather than the hinge. It seems to only achieve a degree of radial evenness at the edge farthest from the "hinge." 

[Fossildude19]

1 hour ago, hemipristis said:

 

The fan-shape with the hinge at the top?  What is radiating gfrom the central point therein could be remnant texture or dendrites, but I've not seen them fan out before.   

 

Note that all through this I said maybe, If it is biological, its been highly altered/recystallized and eroded.  But We shall have to agree to disagree on this one.

The shape is too irregular for me to be convinced it is a brachiopod. 

I agree - we disagree.  

[Auspex]

The shape and texture of this thing is highly suggestive, as is it's apparent symmetry. The size of it, though, at nearly three inches across, would be a gigantic brachiopod!
The rock itself really doesn't look (in the pictures on my screen) like sedimentary rock, either. If it is indeed not, we can put the question of it being a fossil to rest, and call it a geologic oddity (as suggested).

[ynot]

I agree with a hackle fringe fracture that is somewhat eroded.

Not a fossil.

[Carl]

I agree with non-fossil. Looks like a fortuitous fracture.

[Mark Kmiecik]

Why wouldn't the two fractures directly above it in the first photo exhibit similar striation? Also, I've never encountered any rock with the type of grain this has that would fracture in this manner.

[fifbrindacier]

I'm in the geologic camp.

[hemipristis]

6 hours ago, Auspex said:

The shape and texture of this thing is highly suggestive, as is it's apparent symmetry. The size of it, though, at nearly three inches across, would be a gigantic brachiopod!
The rock itself really doesn't look (in the pictures on my screen) like sedimentary rock, either. If it is indeed not, we can put the question of it being a fossil to rest, and call it a geologic oddity (as suggested).

hmm, somehow in all this, I forgot to look at the scale. 3 inches or so across appear to be about right.  That would indeed make it difficult