Hmmm... Not sure! That is something I would recommend taking by a natural museum. They may be able to identify it by site or give you an idea based on how much it weighs. Just a thought. =) Good luck! and if you do find out what it is, let us know.
Saw a show on Discovery that talked about how the bedrock of New York City originated somewhere on the other side of the world (part of the Himalayas maybe?). Would be interesting to see if this rock was part of that migration. Your local or national Geological Society could help identify it.
