basal

a. (Bot.) Having the nerves radiating from the base; -- said of leaves. [ 1913 Webster ]

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. [ 1913 Webster ]

☞ 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. [ 1913 Webster ]

2. An imitation, in pottery, of natural basalt; a kind of black porcelain. [ 1913 Webster ]

a. [ Cf. F. basaltique. ] Pertaining to basalt; formed of, or containing, basalt; as basaltic lava. [ 1913 Webster ]

a. [ Basalt + -form. ] In the form of basalt; columnar. [ 1913 Webster ]