basalt

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A hard, dense, dark volcanic rock composed chiefly of plagioclase, pyroxene, and olivine, and often having a glassy appearance.
2. n. A kind of hard unglazed pottery.

Century Dictionary and Cyclopedia

1. n. A volcanic rock occurring widely, and consisting of a triclinic feldspar, together with augite and magnetite or titaniferous iron. Olivin and nephelin are also often found in the basalts, especially the former. Apatite, leucite, and hauyne are occasionally present. The basalts have been variously classed by different writers. Basalt proper is the dark, compact variety, breaking with a splintery fracture. Under the name dolerite are included all the more coarsely crystallized varieties in which the component minerals can be made out with the naked eye, while anamesite is the name given to those varieties which have a finely granular texture. In the modern eruptive regions basalt has almost always been the last rock to be emitted from the volcanic orifice. The cooling of lava often gives rise to the formation of hexagonal prisms or columns, which are occasionally extremely regular in form and of great size. Basalt displays this structure more frequently and in greater perfectness than any other rock; hence this kind of structure is frequently called basaltic. (See cut.) Remarkable formations of columnar basalt exist in various parts of the world, as the Giant's Causeway on the northeast coast of Ireland, and Fingal's Cave in the island of Staffa, Scotland.
2. n. Proposed as a field term, in petrography, for all dark-colored aphanitie, nonporphyritic (aphyric), igneous rocks. The basalts, thus defined, include many dense andesites, diabases, and numerous lavas commonly grouped as basalt before their varying composition was revealed by microscopical study. Basalt in this sense is opposed to felsite, which includes light-colored rocks. See felsite.

Wiktionary

1. n. mineralogy A hard mafic igneous rock of varied mineral content; volcanic in origin, it makes up much of the Earth's oceanic crust.
2. n. A type of unglazed pottery.

GNU Webster's 1913

1. n. (Geol.) A rock of igneous origin, consisting of augite and triclinic feldspar, with grains of magnetic or titanic iron, and also bottle-green particles of olivine frequently disseminated.
2. n. An imitation, in pottery, of natural basalt; a kind of black porcelain.

WordNet 3.0

1. n. the commonest type of solidified lava; a dense dark grey fine-grained igneous rock that is composed chiefly of plagioclase feldspar and pyroxene