in natural history, is a heavy hard stone, chiefly black or green, consisting of prismatic crystals, the number of the sides of which is uncertain. It is called by English miners cockle, and by Germans scherl. Its specific gravity is to that of water, as 3000 or upwards to 1000. It is considered by Wallerius as a species of the cornus, or horn-rock. Cronstedt enumerates it among the earths which he called garnet earths. Basalt frequently contains iron; and consists either of particles of an indeterminate figure, or of a sparry, flinty, or fibrous texture. Black basalt is called lapis lydias, and is used as a touchstone to show the colours of metals. Basalt has a flinty hardness, is insoluble by acids, and is fusible by fire. — The most remarkable quality of this is its figure, being never found in strata, like other marbles; but always standing up in the form of regular angular columns, composed of a number of joints, one placed on and nicely fitted to another, as if formed by the hands of a skilful workman. See Plate LV. fig. 9. The basalt was originally found in columns in Ethiopia, in fragments in the river Tmolus, and some other places; we now have it frequently, both in columns and small pieces, in Spain, Russia, Poland, near Dresden, and in Silesia; but the noblest store in the world seems to be that called the Giant's Causeway, in Ireland; and Staffa, one of the Western isles of Scotland. In Ireland it rises far up in the country, runs into the sea, crosses its bottom, and rises again on the opposite land. See GIANTS CAUSEWAY, and STAFFA.

The origin and formation of basaltes has much puzzled the world; but we may consider, that many of the known fossil bodies have a property, like salts, of arranging themselves into different figures at the time of their first concretion into a mass. This is from the same laws in nature with that of salts; and we are well assured by daily experience, that crystal and spar, according to this natural determination, ever form regularly angular figures, when all the proper accidents have concurred to their concretion. The most common figures of crystals are the hexangular columns; and those of spar, either trigonal columns or parallelopipeds. The combinations and mixture of these, in different degrees, may naturally produce mixed figures, according to these degrees; and a third substance, though in itself not disposed by nature to assume or arrange itself into any particular figure, if mixed with these, may be able to spread, extend, and enlarge the figures they concrete into, or otherwise alter them. A mixture of three bodies is, therefore, capable of producing a fourth, of a figure different from any one of the three above; and we find also, by many parallel instances, that the quicker or slower passing off of the fluid from whence bodies are concreted, is capable of altering their figures.

The marble of the Giants-causeway, or any other columns of basaltes, is found to be composed of an admixture of crystal, spar, and earth. The spar may be procured in its own form; and the remaining mass, after the separation of the spar, is found to be pure crystal, and an earth of the clay kind, seeming the same with the black pipe-clay of Northamptonshire and some other places, only much blacker. We know very well what would be the figures of these bodies concreted alone; and may thence deduce what may be the possible consequences of their union, and the different accidents attending their concretions. But the opinion which seems most likely to prevail at present is, that this substance is a crystallization from some kinds of volcanic lava. See VOLCANO.