Need help with ID please.

Found in the Green River Formation Northwestern Colorado. Can anyone help with identifying what this may be? Thanks. Attachment 1772286Attachment 1772287Attachment 1772288Attachment 1772289

Hard to say crystal, try an acid test for carbonates and some hardness/streak testing. Does it feel heavy or light compaired to a simular stone? Overall it appears to be something simular to a concretion but it may be a nodule of something like calcite or barite.

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Originally Posted by DDancer

Hard to say crystal, try an acid test for carbonates and some hardness/streak testing. Does it feel heavy or light compaired to a simular stone? Overall it appears to be something simular to a concretion but it may be a nodule of something like calcite or barite.

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I agree. Could be onyx too.