A mafic volcanic rock consisting of calcic- plagioclase feldspar and pyroxene, basalt is the most abundant of all lava types. Apatite and magnetite are nearly always present in small quantities, while olivine may also occur.

TEXTURE A fine-grained rock, basalt has crystals that are both euhedral and anhedral. The crystals, however, are not easy to see, even with a magnifying glass.

ORIGIN Produced by the cooling of highly mobile basaltic lavas. Because of their fluidity, they may form very thick lava sheets. Basalt occurs widely in continental areas and is the principal rock of the ocean floor. One of the beststudied active basaltic volcanoes, Mauna Loa, forms much of the island of Hawaii.

Group: IGNEOUS

Origin: Extrusive

Grain size: Fine

Crystal shape: Anhedral, Euhedral

Classification: Mafic

Occurrence: Volcano

Color: Dark