Coralline algae are prominent among marine plants for their ability to deposit large amounts of calcium carbonate in their cell walls. The mineral is deposited as calcite with high concentrations of magnesium present. In fact, coralline algae are the only marine macroalgae depositing calcite; other calcifying red algae, as well as some green algae, deposit aragonite. However, the paucity of information on the biochemical and physiological aspects of calcification in coralline algae becomes evident when recognizing that in a review on silicification and calcification. Coralline algae contain the cations magnesium, iron, manganese, sodium, strontium, potassium, and barium. Prerequisites for the deposition of calcium carbonate include having appropriately high concentrations of calcium and carbonate as well as an alkaline environment. Three theories have been presented for the process of calcification: (1) carbon dioxide utilization, (2) organic matrix, and (3) bicarbonate usage. The mechanism of calcification in coralline algae probably involves elements of the second and third theory.