in natural history, a solid, dry, opake, inflammable substance, found in large detached masses, of a fine and regular structure, having a grain like that of wood, splitting more easily horizontally than in any other direction, very light, moderately hard, not fusible, but readily inflammable, and burning a long time with a fine greenish flame.

It is of a fine deep black colour, very glossy and shining, except upon its surface, where it has been fouled by accident. When examined by the microscope, it is found to be composed of a number of parallel plates, very thin, and laid closely upon one another. It is not soluble in, nor makes any effervescence with acids. It should be chosen of the deepest black, of a moderate hardness, very light, and such as will split most evenly in an horizontal direction; this being its great characteristic, by which it is distinguished from the cannel coal, which breaks equally easy any way.

Jet is of great use to perfumers, and is sometimes prescribed in medicine. Dioscorides tells us, that it is an excellent emollient and diuretic, and recommends a fumigation of it for diseases of the womb; and among the eastern nations, it is still in high repute as a cordial, a strengthener, and prolonger of life.

Every pound of jet pays on importation a duty of 7½d. and draws back 6½d. on exportation.