Two different cristallographical forms of calcium carbonate (aragonite and calcite) has been identified in mussels with Raman spectroscopy.
CitacióFerrer, P. [et al.]. Molecular stratigraphic analysis with Raman spectroscopy of the shell of a mussel. A: International Workshop on Marine Technology. "MARTECH 2013: 5th International Workshop on Marine Technology: 19th-20th of November, Vilanova i la Geltrú". Girona: 2013, p. 82-84.