Seeing a 305 million-year-old prismatic surface on a piece of the shell seems remarkable to me. After all that time, the shell surface still presents with a shimmer that captures and refracts light in several different directions. The views below show edge details and a close-up of the individual standing polygon columns of calcite.
Whole piece 
Edge detail showing standing layer 
Close up of the shimmering layer 
Another view of the edge 
More of the shimmering layer 
Detail of the shimmering layer. Individual geometric spines standing on edge capture the light. 
