An igneous rock that contains a relatively high concentration of the alkali (lithium, sodium, potassium, rubidium, caesium, and francium) and alkaline earth metals (magnesium, calcium, strontium, barium, and radium). Both silica-saturated and silica-under-saturated varieties exist, expressed in the presence of alkali feldspars and feldspathoids respectively. Alkali ferromagnesian minerals are usually present, and their identity depends on the composition of the rock. Compare acid rock.
Subjects: Earth Sciences and Geography — Ecology and Conservation.