
Every so often a fossil, generally a fossil shell such as a clam, will break open to reveal a hollow interior filled with crystals, like the inside of a tiny geode. They're usually calcite crystals that grew there, inside the empty shell, during the fossilization process.
The one above I found at Rio Dell, California -- I found it already broken open. It's likely some of my nice complete fossils have crystals within them as well, although I haven't wanted to break them open to find out!
The one above I found at Rio Dell, California -- I found it already broken open. It's likely some of my nice complete fossils have crystals within them as well, although I haven't wanted to break them open to find out!