Alkaline_basalt
Alkali basalt
Type of volcanic rock
Alkali basalt or alkali olivine basalt is a dark-colored, porphyritic volcanic rock[2] usually found in oceanic and continental areas associated with volcanic activity, such as oceanic islands, continental rifts and volcanic fields.[3] Alkali basalt is characterized by relatively high alkali (Na2O and K2O) content relative to other basalts and by the presence of olivine and titanium-rich augite in its groundmass and phenocrysts, and nepheline in its CIPW norm.[4][5]