Calcium compounds are most commonly found in sedimentary rocks such as limestone, chalk and marble where calcium carbonate minerals such as calcite and dolomite are present.
"Ahu" are stone platforms on which many moai sit. There are 313 known ahu and 125 of these carry moai. The biggest, Ahu Tongariki is 220 m (720 ft), and had the most (15) and tallest moai.