Basalt
BASALT', noun bazalt'. [Pliny informs us that the Egyptians found in Ethiopia, a species of marble, called basaltes, of an iron color and hardness, whence it received its name. Nat.Hist.Lib.36.Ca.7. But according to Da Costa, that stone was not the same which now bears the name of basalt Hist. of Fossils.p.263. If named from its color, it may be allied to the Fr. basane, tawny. Lunier refers it to the Ethiopic basal, iron, a word I cannot find.]
A dark, grayish black mineral or stone, sometimes bluish or brownish black, and when withered, the surface is grayish or reddish brown. It is amorphous, columnar, tabular or globular. The columnar form is straight or curved, perpendicular or inclined, sometimes nearly horizontal; the diameter of the columns from three inches to three feet, sometimes with transverse semi-spherical joints, in which the convex part of one is inserted in the concavity of another. The forms of the columns generally are pentagonal, hexagonal, or octagonal. It is sometimes found also in rounded masses, either spherical, or compressed and lenticular. These rounded masses are sometimes composed of concentric layers, with a nucleus, and sometimes of prisms radiating from a center. It is heavy and hard. The pillars of the Giant's causey in Ireland, composed of this stone and exposed to the roughest sea for ages, have their angles as perfect as those at a distance from the waves. The English miners call it cockle; the German, shorl, or shoerl. It is called by Kirwan, Figurate Trap, from its prismatic forms.