Ba"sal (&?;), a. Relating to, or forming, the base.
Basal cleavage. See under Cleavage. -- Basal plane (Crystallog.), one parallel to the lateral or horizontal axis.
Ba"sal-nerved` (&?;), a. (Bot.) Having the nerves radiating from the base; -- said of leaves.
Ba*salt" (&?;), n. [L. basaltes (an African word), a dark and hard species of marble found in Ethiopia: cf. F. basalte.] 1. (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.
It is usually of a greenish black color, or of some dull brown shade, or black. It constitutes immense beds in some regions, and also occurs in veins or dikes cutting through other rocks. It has often a prismatic structure as at the Giant's Causeway, in Ireland, where the columns are as regular as if the work of art. It is a very tough and heavy rock, and is one of the best materials for macadamizing roads.