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High grade black flint?/obsidian, maybe?

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  • High grade black flint?/obsidian, maybe?

    This piece of rock is very shiney. It doesn't seem glassey enough to be obsidian, but it has a high sheen gloss. Would like to know what it is.

  • #2
    That's not obsidian, it looks Zaleski / Coshocton.

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    • #3
      Hi Pam
      I have no idea what Zaleski/Coshocton might be (Matt are those some kind of local names for a variant of something I would recognise?)
      With the caveat that I still feel it's asking a lot to identify a rock from a picture, it looks like "Pitchstone" to me. Pitchstone is glassy like obsidian but duller and with a much coarser texture. The lustre is normally described as "resinous", which is what I see here. It also normally contains lots of "phenocrysts", apparent as little inclusions that stand out like tiny pimples from broken surfaces. I think I can see those - particularly in the third pic.
      Pitchstone is essentially an extrusive volcanic glass but is formed from viscous lava or magma that has cooled rapidly.
      Roger
      I keep six honest serving-men (they taught me all I knew); Their names are What and Why and When and How and Where and Who.

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      • #4
        It's not hard to identify certain materials from an image if you're familiar with their origins.
        Zaleski is a chert type that occurs in her area.  It's usually pitch (glossy) black to gray in coloration.  Zaleski is related to Upper Mercer (Coschocton)and it does get mistaken for volcanic materials sometime (Dacite or obsidian mainly).

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        • #5
          I'd have to agree that it is Coshocton, a fairly common lithic in Ohio.

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          • #6
            Thanks.  Probably is Coshocton.  Live fairly close to there. 
            Looked at pitchstone on a website, and seeing another piece of that type rock, it doesn't bear much resemblance. 
            Didn't look to be obsidian, but I didn't know what it was.  Didn't seem glassy enough for obsidian.  Glad to know what it is.

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            • #7
              Thanks for the heads up on what Coshocton is.
              Not challenging the opinion in any way, but just for information... pitchstone in its various forms:

              Click image for larger version

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              This illustrates why I feel its so dangerous trying to identify a rock from a picture, unless as Matt says you have locality/origin knowledge and expertise.
              and a couple of pitchstone artefacts for good measure:

              Click image for larger version

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              Roger
              I keep six honest serving-men (they taught me all I knew); Their names are What and Why and When and How and Where and Who.

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