in natural history, a kind of semitransparent 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 steel; calcinable by fire, after which they become white, friable, and, according to Henckel, 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 Tschirnhausen'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, no 1069.

This genus of stones, or siliceous earths, Cronstedt considers as of an intermediate nature between the quartz and jasper; both of which it so nearly resembles, that it is difficult to distinguish them. Our author characterizes it in the following manner: 1. It is more uniformly solid and not so much cracked in the mass as quartz, but more pellucid than the jasper. 2. It bears the air better than the jasper, but worse than the quartz. 3. For the purpose of glass-making it is better than jasper, but not quite so good as quartz. 4. Whenever it has had an opportunity of shooting into crystals, those of quartz are always found in it; as if the quartz made one of its constituent parts, and had been squeezed out of it. This may be seen in every hollow flint and its clefts, which are always filled up with quartz. 5. It often shows most evident marks of having been originally in a soft and slimy tough state like jelly.—To these properties the following are added by other authors. 7. When broken, it is scaly, generally unequal, and cracks into thin lamellae. 8. In a calcining heat it becomes opaque, white, and milky.

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 broken into regular figures. But we know not that this art hath been anywhere described.