Answer: aragonite

AnswerCrossword Clue
ARAGONITECalcium carbonate.
ARAGONITEMineral similar to calcite.
aragonitemineral, orthorhombic calcium carbonate, CaCO3, chemically identical with calcite but differing in crystallization and in having a higher specific gravity and less marked cleavage
aragonitean orthorhombic mineral composed of calcium carbonate also ARRAGONITE