SPAR, a name given to those earths which break easily into rhomboidal, cu bical, or laminated fragments, with po lished surfaces. As the term spar is thus applied to stones of different kinds, with out any regard to the ingredients of which they are composed, some additional term must be used to express the constituent parts as well as the figure. The spars found in Britain and Ireland are of four different species: opaque, refracting, dia phanous, and stalactical. A species of spar has also been found in the East In dies, which, from its extreme hardness, approaching to that of a diamond, is call ed adamantine spar. It was discovered by Dr. Black, of Edinburgh, to be a dis tinct species. There are two varieties ; one of them comes from China, and crys tallizes in hexagonal prisms without pyra mids, the length of the sides varying from six to twelve lines, their breadth be ing about nine, of a grey colour, with dif ferent shades. Though the entire pieces are opaque, the thin lamina: are trans parent, and, when broken, its surfaces appear slightly striated. Its crystals are covered with a very fine and strongly ad hering crust, composed of scales of sil very mica, mixed with particles of red felspar. Sometimes the surface has mar tial pyrites or yellow sulphuret of iron adhering to it. Its hardness is so great, that it not only cuts glass as easily as the diamond, but even scratches rock crystal and other very hard stones. Its specific
gravity is to that of water as 2.7 to 1.0. Sometimes it contains crystallized grains of magnetic oxide of iron, which may he separated from the stone, when pulveriz ed, by means of the loadstone. The other . kind, found in Hindoostan, is of a whiter colour, and of a more laminated texture than the former. The grains of iron con tained in it are likewise a smaller size than those of the former ; they are not diffused through its substance, but only adhere to its surface. This spar is ex ceedingly difficult to analyze. M. Mor veau appears to have ascertained that this atone is also found in France. A small bit of it was tried in the presence of Mr. Wedgewood, and he found that its spe cific gravity was superior to the spar of China,_ being no less than 4.18; and the true adamantine spar of China gave 3.82.
Although the word spar seems to include almost all the earthy crystallized minerals that are met with in metallic veins, yet mineralogists have generally agreed to apply the term to those minerals, whether earthy or metallic, which are crystallized, and have a visible foliated texture. Hence we have felspar-spar, fluor-spar, &c. Some of the spars have already been described in their alphabetical order; others we shall enumerate here.