Agate (Replaced Gastropod Shells)

Agate from replaced gastropod shells at Assa, Morocco is an example of fossil preservation where the original shell was gradually replaced by silica. The shell’s internal structure and shape were preserved while agate filled and replaced the original material.

Assa is located in southern Morocco, a region known for fossil-bearing sedimentary rocks and a variety of silicified fossils. These specimens are interesting because they combine fossil and mineral formation in the same piece, preserving an ancient gastropod in agate.