Silurian shell?

[The Goatlady]

My parents built a house into a hillside of glacial till in SE Wisconsin. The area is known for Silurian fossils. I find a lot of corals, crinoids, clam-like critters. Many of the fossils are in chert. Some are crystalized. I just pick them up as they erode out of the hillside.

I found this is a pile of sand/gravel/dirt that the contractor left next to the driveway. At first I thought it was a piece of plastic. I took it to the university geology department. A drop of liquid (vinegar? I can't remember) fizzed and she told me it was made of calcium carbonate.

It is an odd shape with straight ridges. I can't photograph under a microscope (although I'll give it a try) but the blue color is made up of very bright blue crystals that look like sugar - like the colored sugar you might put on cookies.

There are some layers of slightly shiny material on the brown side.

[The Goatlady]

Hers' some more pix.

[The Goatlady]

And a few more .

[Auspex]

Huh...

The blue looks for all the world like paint overspray.

[lissa318]

Do any abalone shells have colored textured areas on them like that maybe?! Just a guess...

I'd like to add that I am not suggesting fossil abalone shell. They can travel we had one in our garden at our last house that is probably still there. lol.

Edited March 10, 2016 by lissa318

[The Goatlady]

I know. I thought it was plastic but it came out of the soil from a house/basement excavation. The pit was 12 feet deep. Before this the land was pasture for the last several decades. And, like I said, the blue looks like very brilliant blue sugar crystals under the microscope. I also found a chunk of raw copper, not worked by man. There is a name for these copper nodules but I can't think of it right now. The copper piece has the blue-green patina you'd expect. I don't have a microscope handy but I remember the "sugar" crystals being in straight lines.

[Peat Burns]

Maybe a bit of concrete with an imprint of burlap or something on it? Concrete would fizz in acid.

[The Goatlady]

No. The texture is nothing like concrete.

[amphipod]

Placoderm shell fragment?

[The Goatlady]

You may be on to something.I googled up some photographs of placoderm plate fragments and it's the closest thing I've found to the texture of it.

Under normal light the blue color is more flat looking. I was using a flash on the kitchen table last night to get the pictures. A flash would probably be daylight balanced, that is, the color of the light would be closer to sunlight than the LEDs I have. It really gives it more of a metallic blue, closer to the color of the crystals under a microscope.

[Peat Burns]

Native American pottery fragment?

[Auspex]

Native American pottery fragment?

Possibly the best theory so far!

[amphipod]

You may be on to something.I googled up some photographs of placoderm plate fragments and it's the closest thing I've found to the texture of it.

Under normal light the blue color is more flat looking. I was using a flash on the kitchen table last night to get the pictures. A flash would probably be daylight balanced, that is, the color of the light would be closer to sunlight than the LEDs I have. It really gives it more of a metallic blue, closer to the color of the crystals under a microscope.

I just read of another organism that also looks quite similar, spatiopora.

[The Goatlady]

Pottery was a consideration. Looking at the detail of the line of ridges on the "front", I'm not so sure. Think about what it would take to make those ridges by hand. Our fingers and tools are kind of big to pull that off. Remember the Hochunk did not have a 3D printer. Additionally, is clay made up of calcium carbonate? I suppose those elements could be in clay. Anyone know for sure?

Spatiopora fossils do show patterns on the shells so that might be a good direction to look.

It's such an odd shape. Figuring out the internal structure of different shells might be of value. It's also possible that its shape changed some over time.

[Peat Burns]

Pottery was a consideration. Looking at the detail of the line of ridges on the "front", I'm not so sure. Think about what it would take to make those ridges by hand. Our fingers and tools are kind of big to pull that off. Remember the Hochunk did not have a 3D printer. Additionally, is clay made up of calcium carbonate? I suppose those elements could be in clay. Anyone know for sure?

Spatiopora fossils do show patterns on the shells so that might be a good direction to look.

It's such an odd shape. Figuring out the internal structure of different shells might be of value. It's also possible that its shape changed some over time.

True regarding forming such details by hand, but the Native Americans often used objects from nature that were pressed into the material before it hardened. I have pieces that have fern impressions, bark, etc. It's not inconceivable that even textiles were used for such decoration. I'm not sure what it is, but I'm not getting a fossil vibe. I could obviously be wrong, but from the pics and circumstances, I'm skeptical about it being a palaeozoic fossil.

[The Goatlady]

I hear you. It is a really weird piece. If the blue is a man applied pigment, could it explain the crystals when viewed microscopically?

[The Goatlady]

I sent an email off to the state archeology office. We'll see what happens.

[JohnJ]

I don't think this is any kind of native artifact fragment. I do think your initial thoughts about it being plastic are more likely. It looks partially charred and melted. The first photo in post #3 seems to show some "folding" of the material. Maybe you could offer a better description of that, having it in hand.

If a drop of vinegar fizzed, it could be the result of material trapped in the "charred" area. Some additional images of the 'back' side might be useful.

Edit: Can you get a clear shot of the "chipped" area?

[The Goatlady]

I will try to get better pictures. My camera does not want to focus when I zoom in and when I get close I block out the light. By close, I mean less than 2 inches.

A University of Wisconsin geology professor identified it as calcium carbonate. She put a drop of something on the chip. The chip is a pure white and a consistent small grain material. A quick google revealed that Calcium carbonate could easily be in pottery. Cobalt and copper could make things blue. I did not determine if Co and Cu could make things blue spontaneously.

The areas suspected of being charred are all tones of brown, not black. Toast and cheese also brown, if we're lucky, when they are cooked. So I'm not saying it's not charred. Just not black.

The backside has a couple spots of thin layers that could be a mother of pearl like material. It has some shine but I'll need to find my magnifying glass to look for iridescence.

It does have a shape like it was flat and someone gave it a partial twist. However, it is not the same thickness over the length, which is about 2 inches. On the back, there is actually a structural wedge of material - all smooth in the wedge - there is not a a separate piece stuck on. The backside of it reminds me of the nooks and crannies you'll find on the hinge area of an clam, scallop, or oyster.

It feels a little sticky if I touch it to my tongue but it does not adhere enough to stay there on its own.

[engineeringstudent]

It feels a little sticky if I touch it to my tongue but it does not adhere enough to stay there on its own.

Almost lost my tea...

[The Goatlady]

Haha!

I meant the dry kind of sticky. You know, when something is porous as opposed to a non-porous plastic or glazed pottery, etc.

That did come out kind of weird.

[The Goatlady]

A couple more views.

[The Goatlady]

More pix

In one of the pictures with my hand in it, the blue mystery object looks like it's wrapping across my finger like a wet noodle. But when you look at the back, you can see the angle and the structural wedge shape.

[Peat Burns]

I don't think this is any kind of native artifact fragment. I do think your initial thoughts about it being plastic are more likely. It looks partially charred and melted. The first photo in post #3 seems to show some "folding" of the material. Maybe you could offer a better description of that, having it in hand.

If a drop of vinegar fizzed, it could be the result of material trapped in the "charred" area. Some additional images of the 'back' side might be useful.

Edit: Can you get a clear shot of the "chipped" area?

A match or lighter ought to solve the question if it's plastic or not.

[JohnJ]

A match or lighter ought to solve the question if it's plastic or not.

Good point. A red hot needle should do the trick. At least one possibility would be eliminated.