One of several Montastrea samples taken from an internal reef outcrop off the east coast of Andros Islands, Bahamas, exhibits recrystallization of the aragonitic skeleton to micritic high-Mg calcite (12.5 to 15.3 mole percent MgCO3). The recrystallization is accompanied by cementation. The coral structure is destroyed during the micritization process. Aragonite needle cement, precipitated prior to micritization, remains unaltered. Because this is not a process generally found in nature, a nonequilibrium precipitation of high-Mg calcite is likely. The differential replacement of the aragonitic skeleton and the aragonite needle cement may reflect differences in strontium content that may result from differences in the chemistry of pore solution and sea water.