This is a great example of a therapod gastrolith tooth. This means this is a spitter tooth that happened to have been broken out while eating then digested along with its prey. Therefore all the enamel that was once on the tooth was digested off leaving you with an awesome tooth core. This particular tooth most likely belonged to the most efficient predator to ever walk the earth the Allosaurus.
Location: Moffit county, Colorado
Size: 1inch x .5inches