Calc-alkali basalt
Calc-alkaline basalts are rich in Ca, Mg and Na, crystallising olivine , augite and plagioclase , and make up a major portion of continental crust . It is commonly associated with andesite s and dacite s in orogenic belt s and island arc s. Basalts from the calc-alkaline magma series are distinguished from those in the tholeiitic magma series by the redox state of the magma they crystallized from: tholeiitic magmas are reduced, and calc-alkaline magmas are oxidized enough to precipitate significant amounts of magnetite .