ARSENICAL MINERALS occur chiefly in primitive rocks, and frequently associated with other metalliferous minerals.—Natire arsenic, although nowhere very abundant, is not unfrequently found in mines in Europe, Asia, and America, generally along with sul phur and metallic sulphurets. In Britain, it occurs at Tyndrum in Perthshire. It has usually a fine granular character. It is very seldom, if ever, quite pure, usually con taining a little antimony and iron, and not unfrequently a very little silver or gold.—A very similar, and still rarer mineral, found in similar situations, is known as arsenic antimony, and consists of about two parts of metallic arsenic, and one of metallic anti mony.—Arsenic-silver, or arsenical silver, is another very rare mineral, consisting chiefly of arsenic and iron, but containing also about 13 per cent of silver and a little antimony. —Arsenie-glance, found at Marienberg in Saxony, and containing about 3 per cent of bis muth, has the rematkable property of taking fire at the flame of a candle.—Arsenious acid occurs native in a few localities in Germany and France, and as a mineral species, has received the name of arsenite, which perhaps too closely resembles the chemical designation of its acid, another compound of arsenic and oxygen containing more oxygen than arsenious acid, although it does not itself occur native, is not infrequent in the form of compounds with copper and lead (arsenates of copper and lead), which enter into the composition of a number of minerals, none of them so abun dant as to be of any importance.—Among A. 31. are also to be ranked the compounds
of arsenic with sulphur, particularly orpiment (q.v.), railcar (q.v.), and dimorphine, rarer mtneral than the other two, and therefore less important.—But the most important of all A. M., because of their use as ores of arsenic, for the preparation of white arsenic, or arsenious acid, are those in which arsenic is combined with nickel and cobalt. One of these is arsenical pyrites, or leucopyrite, found in various mines of the continent of Europe, and containing arsenic, iron, sulphur, nickel, and cobalt, in somewhat various propor tions—the arsenic, however, always the principal constituent. It generally occurs alas sive. —.1fispickel, which frequently occurs in rhombic crystals, but often also massive, differs from it in containing a considerable quantity of silver, so that it is used both as an ore of arsenic and of silver. It is found in many of the tin-mines of Cornwall, and is pretty frequent in different parts of the world. —Nickel/7u' consists of nickel and arsenic, and is used-as an ore of nickel, and also for the preparation of white arsenic. — Cohaltine and smaltine—the former consisting of cobalt, sulphur, and arsenic; the latter, of cobalt and arsenic—arc used for the preparation of blue colors for porcelain and stoneware. Both are found in Cornwall; they occur also in some of the mines of the continent of Europe, and in other parts of the world.—The presence of arsenic in a mineral may commonly, be detected by the alliaceous odor which it emits before the blowpipe.