This is a lot of fossil seashell casts made of replacement calcite. These odd specimens are formed when a seashell fossilizes under certain conditions. Over a long period of time, the shell is completely replaced by minerals, leaving behind a cast of the original shell. In this case, the casts are made of calcite. One of the casts (the largest one) has botryoidal crystals on the hollow interior - this is difficult to capture with a camera, but some of these crystals can been seen in the second photo. This calcite is translucent when held up to a light and has a dark olive green color from river tannin staining. There are three (3) casts in this lot.
Smaller casts of seashells are quite common in Florida's fossils deposits, but large casts containing botryoidal crystals are quite rare. These pieces likely date from the Miocene epoch (approx. 5,000,000 to 23,000,000 years ago). These were recovered from the Peace River, Bone Valley Formation, Hawthorn Group, Florida.
Refer to the photos. The black centimeter cube is shown for scale and is not included. You are purchasing all of the casts shown.