Figure 4.

Schematic illustration showing the three common processes that make up ion pathways in the biomineralization of coccolithophores, sea urchin larvae, and vertebrate bone. These pathways involve ion uptake, cellular manipulation and deposition of the mature mineral phase. The Y-axis shows the approximate calcium concentration ranges in which these three processes operate. The solid lines indicate known processes and dotted lines indicate putative ones. Question marks highlight yet uncharacterized stages in the pathway. Note the enormous calcium concentration range for mineralizing cells. Irrespective of whether the mature mineral phase is a carbonate or phosphate mineral, the ion pathways all involve calcium, carbonate and phosphate as is schematically illustrated by the blend of colors for the different ions.