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Found this in beach gravel while on lunch break. 




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In my thought, it could be igneous rock, maybe porphyritic with phenocrysts.

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I encounter shale that looks just like that a Red Hill site in Pennsylvania. In the rock the mottled Reddish brown shale and Greenish grey shale are from changes in the rock chemistry in lithification.

Organic matter can reduce the Iron content from Ferric oxidation state (Fe +++) to Ferrous oxidation state (Fe ++). The two colors of each Iron Oxide state, corresponds to the Red and Green. I am fairly sure that is what is going on in your rock specimen. 

hyner scale.jpg

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Might one think of it as a fossiloid ? Or is there seriously a term which describes situations like this ?

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