Coral fragments have been found in Koko and Salt Lake rocks, and metamorphic rocks included in the volcanics may be part of the basement that the magmas of the volcanoes traversed. Calcite - which in the form of crystals gives Diamond Head its name - in the volcanic rocks may come from coral reefs, groundwater or even from the magma itself; isotope ratios of the rocks indicate that groundwater carbonates are the most important source, however.