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817 Views 1 Reply Last post: Feb 7, 2014 1:53 PM by MikeHardman RSS
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Feb 7, 2014 11:59 AM

Unknown Rock/Fossil

One of my middle school students brought in this fossil in hopes of a positive identification. The only information he was able to provide was that it was found along or near a beach in California. I have provided some pictures below. If anyone can shed some light as to what you believe the object is composed of or what could have caused to bone-like markings, I would greatly appreciate it! Thanks so much.


  • Currently Being Moderated
    Feb 7, 2014 1:53 PM (in response to Elmer)
    Re: Unknown Rock/Fossil

    The dark and light parts are most probably made of a very similar material to the matrix, because there is no differential weathering/erosion between them.


    I think they're shell fragments in a dark grey limestone matrix. That is, I am suggesting it is a bioclastic limestone, though that is a fairly broad term.


    You can test for carbonate using vinegar or a 5-10% HCl solution (if you have conc. HCl, be careful how you dilute it). See this for more on acid testing -



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