HORN stone, or HORN steen, in minera logy, a species of the flint genus, divided by Werner into three subspecies: the splintery, the conchoidal, and the wood stone. The most common colour of the splintery horn stone is gray; it is found in veins, in the shape of balls, in lime stone, and forming the basis of porphyry, in several parts of Germany, and also in the Shetland islands. It appears to differ from quartz in Containing a greater proportion of alumina; when it Contains a very large quantity, it passes into jasper. It sometimes borders on chalce dony and flint. The best millstone, called French burr, is cellular-splinter horn stone. Conchoidal hornstone occurs in beds, accompanied with agate; and is distinguished from the splintery by the lightness of its colours, its fracture, and its inferior translucency hard ness.
In the wood.stone several colours occur together, and it commonly exhibits co -loured delineations, as clouded and strip ed, and these themselves in the direction of the original woody texture.
Its shape is exactly conformable to its for mer woody shape, so that it occurs in the form of trunk, branches, and roots. It is found in sandy loam, in Germany, and in Ireland. It receives a good polish, and serves the purpose of agate.
Mr. Jameson observes, on this mineral, that, " at first sight it may appear incon sistent, ter consider a petrifaction as a par ticular fossil species; When we reflect, however, that woodstone differs in its ex ternal characters from all other fossils, the justness of the Wernerisn method will become evident. Many other fossils occur in the shape of petrifactions,.but they are almost always identical with some known species, and therefore are to be considered only as Varieties of the exter nal shape of the particular fossil to which they belong.
HonN work, in fortification, an out-work compdsed of two clemi.hastions, joined by a curtin.