- an assemblage of rocks, rich in silica and magnesium, that constitutes the lower layer of the earth's crust and is found beneath the ocean floors and the sial of continents.
- the uppermost member of a full classical order, usually a cyma recta, representing a roof gutter; cymatium.
- the silicon-rich and magnesium-rich rocks of the earth's oceanic crust, the most abundant individual rock being basalt
- the earth's continental lower crust, probably comprised of gabbro rather than basalt
