Inoceramids had thick shells composed of "prisms" of calcite deposited perpendicular to the surface, and unweathered fossils commonly preserve the mother-of-pearl luster the shells had in life.
Inoceramids, with their distinctive shell structure made of calcite prisms deposited perpendicularly to the surface, are known for their unweathered fossils retaining a mother-of-pearl sheen.