in natural history, a kind of semi-transparent, or quite opaque stones; generally of a roundish form, and covered with white crust; of a smooth, uniform, shining texture; so hard, that they will strike fire with flint; calcinable by fire, after which they become white, friable, and, according to Hemckel, heavier than before, and soluble by acids; vitrifiable only by the very violent heat of the largest speculums, such as that of Villette, and not even by the focus of one of Tchirnhausen's lenses, according to an experiment of Neumann. They are found generally in beds of chalk and of sand; but never forming entire strata of rock as jasper does. By long exposure to air and the sun, they seem to decay, to lose their lustre, their firmness of texture, and to be changed to a white calcareous earth or chalk. Hence they are almost always found covered with a white chalky crust. They are also convertible into a calcareous earth by fusion, or vitrification with so much fixed alkali, that they shall resolve into a liquid mass called the liquamen or oil of flints, and by precipitation from the fixed alkali by means of acids. See Chemistry, n° 338.

Flints are of the class of earths called vitrifiable, because these earths are generally employed, together with fixed alkali, as materials in the making of glas. See Glass.

Breaking of Flints. The art of cutting, or rather breaking, flint-stones into uniform figures, is by some supposed to be one of the arts now lost. That it was known formerly, appears from the ancient Bridewell at Norwich, from the gate of the Augustin friars at Canterbury, that of St John's Abbey at Colchester, and the gate near Whitehall Westminster. But that the art is not lost, and that the French know it, appears from the platform on the top of the royal observatory at Paris; which, instead of being leaded, is paved with flint cut or broke into regular figures. But we know not that this art hath been anywhere described.