interesting composite coal like rock with white veins and gold streaks in lake Erie

ciela

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Aug 7, 2019
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New York
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Hi all ~ I have found a very interesting rock on the shore of Lake Erie and am curious if anyone has ideas as to what it might be. I know nothing really about geology and rock identification but this seemed like a good place to start.

The place where it was found is called Evangola State Park, in New York state. I found it rolling in the waves on a sandy beach right at the edge of a cliff of sedimentary rock that was mostly greyish layers that break off easily and when rubbed turn quickly into a slimy clay like substance in the water. Ive added an image of the location as well as a few pictures of the rock in the sun and in the shade. As you can see from the pictures, it is black and seems layered but does not flake easily like mica. when the black parts are scratched with metal it scrapes off easily becoming powdery, and if rubbed on paper leaves a black mark. The white veins running through it are harder but also break apart fairly easily if scraped with metal, probobly because they are extremely thin veins running through. On one side there is a grey streak of harder rock that is the same greyish rock that makes up the sedimentary rock layers of the cliff show in the picture on the shore of lake Erie. This greyish rock when wet from the waves could be rubbed and would quickly turn into a slimy clay like substance with friction and water. On the other side of the rock there is a gold/brass colored streak that shimmers brightly in the sun but appears more dull brownish in the shade or shimmers at the right angle.

Super interesting sample with a lot going on, as I said I am not really a rock hunter and I have little knowledge of geology but it's a super interesting specimin with a lot going on so I was curious to learn more. Let me know if you have ideas! Thanks :)

evangola-st-park.jpgerierock1.jpgerierock2.jpgerierock3.jpgerierock4.jpgerierock5.jpg
 

Cool specimen, awesome looking location, thanks for the pics.:icon_thumright:
Steve.
 

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Looks kinda like a mudstone. I know it had a specific name, but cant remember right now.
 

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Yep ~ the cliffs were definitely some type of mudrock, thanks for the reference. Looking at the wikipedia it lists five types of "Mudrock" claystone, mudstone, siltstone, shale, and slate. I'd say from the pictures the cliffs at Evangola are mostly siltstone by the grey coloration and the way they melt away into a slimy goo when you wet and rub them. A lot of layers of shale also judging by the picture of "Marcellus Shale" in the wikipedia. Wiki page specific to the "Marcellus Formation" or Marcellus Shale shows on a map that this is exactly in the area of New York where I found the rock so definitely consistent. Says the Marcellus was deposited almost 400 million years ago during the development of land plants -- the black rocks are black because high organic matter content. So -- I'm assuming the rock I found, which is black but definitely closer to coal than the shale, must have been a pocket of organic matter. Still not sure about the gold streaks and harder, white mineral veins though. Very cool

Marcellus Formation Wiki
Mudrock Wiki
 

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