Dictionary of Human Evolution and Biology

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1. calcium carbonate, a common mineral form of limestone, a rock that possesses an internal crystal face that produces a preferential cleavage plane and that makes it difficult or impossible to control fracture and to produce a sharp-edged tool.

2. with aragonite, one of the two common carbonates of calcareous (chalky) skeletons; aragonite disappears almost completely from older fossils, whereas calcite may be replaced by silica or pyrite, a process known as permineralization.

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