Found on beach. ID? Can i break it open?

[Cai]

[Mark Kmiecik]

What you found appears to be an internal mold of an ammonite or gastropod or similarly shaped shell. Don't break it open. There's nothing inside but matrix. This is as good as it will get. Is the opposite side similar? If not, it may only be a suggestively shaped concretion. If that's the case, then go ahead and break it open. Some concretions contain fossils. Most don't. Good luck.

[Cai]

Thanks