The Giant Venus Clam fossil (aka Mercenaria permagna) found in the Fort Drum Member, Nashua Formation of Florida. It was described by Conrad in 1838 and can also be found in North and South Carolina. This creature lived in the Calabrian Stage (780,000 years ago to 1.8 million years ago) of the Pleistocene Epoch of the Quaternary period..
This specimen contains calcite crystals like a geode. Thanks to Mary Ann for the specimen.
These last two pictures are of the dogtooth spar calcite that occupies the inside of the fossil shell. It is a honey colored calcite.