Found this on the beach, it definitely was a shell at one point. Looks to have little crystals inside. Is there a name for something like this? : r/ fossils
Unraveling How an Extinct Mollusk Got Its Strange Shell - The New York Times
Florida Fossil Shells - Fossil ID - The Fossil Forum
The Rock Gallery About fossils
Fossils: History And Geology In A 'Shell' | Village Rock Shop