Fossil Shell Crystallized In Its Nodule - France

Pretty fossil nodule (oncoid) of a Turritella (marine gastropod) surrounded by a concentric concretion of past bacterial activity.
Nodule sawn in two, revealing the coil of the gastropod whose interior is crystallized.
Both cutting surfaces are polished, offering a diversity of colors and details.
Age: Eocene (2nd epoch of the Tertiary Era), - 56 to - 33.9 million years.
Origin: Aude (11) - France
Height: approximately 7 cm.
Coming from a former private paleontological collection. High quality fossil.
Uncommon.
Presented for photography on a plexiglass base, available if needed.
Geologically, the formation of such a nodule begins around a core (the empty shell of the mollusk, or any other hard body, like gravel itself) of which the action of cyanobacteria (close to stromatholiths) causes thin concentric layers to crystallize laminar, calcareous in nature. This set is called “oncoid”.