PYRITES. Iron, in combination with sulphur, forms a mineral substance, which has been long known under the name of Pyrites, and which is very extensively dif fused. it occurs massive, disseminated, and frequently crystallized : the forms of its crystals are various, but the most com mon is the cube regular, or modified by truncation of the angles or edges, or ac cumination of three planes on the angles: the octaedron, dodecaedron, and icosae dron, also sometimes occur.
Its colour is brass-yellow, varying a lit tle in the shade, and the lustre is always fully metallic : it is opaque. The frac ture is uneven. It is brittle ; its hardness is such as to strike fire with steel ; its spe cific gravity is from 4.6 to 4.8. By fric tion it exhales a sulphurous smell. This odour is strong when it is heated before the blow-pipe ; it gives at the same time a blue flame ; and at length a globule of a brownish colour. It is soluble in nitric acid, with the disengagement of red va pours. It is not sensibly magnetic. Va rious analyses of it have been given : ac cording to those executed by Mr. Hatch et, it consists of Sulphur 52 Iron 48 100 Besides this, which may be named com mon Pyrites, there are some others which may be regarded as varieties of the spe cies, and which differ principally in struc ture, or in the form under which they occur. The striated or radiated pyrites presents a striated fracture, the stria be ing generally diverging.
It is rather more liable to tarnish than the preceding, and decomposes more readily in a humid atmosphere. Accord
ing to Mr. Hatchet's analysis, it consists of Sulphur 54 Iron 46 100 • c=== The capillary pyrites occurs in delicate capillary crystals, grouped, parallel, di verging or interwoven, slightly flexible, having a metallic lustre, and a colour passing from yellow to steel-grey, There is, lastly, the hepatic pyrites, so named from the liver-brown colour which it as sumes from exposure to the air. In the fresh fracture its colour is pale brass-yel low, inclining to steel-grey. It occurs massive, of various imitatiye forms, and crystallized in six-sided prisms, or six-ski ed pyramids : it has less lustre than the others, and is more subject to decompo sition. What has been named magnetic pyrites, distinguished, as the name im plies, by its magnetic quality, of which the others are destitute, has been consi dered as forming a distinct species. Its colour is deeper, being intermediate be tween brass-yellow and copper-red, and approaching even to brown, often tar nished : its lustre is also inferior, hut is still metallic. It occurs only massive or disseminated. Its fracture is compact: it is hard and brittle : its specific gravity is 4.5. It appears from Mr. Hatchet's ana lysis of it to differ from the other iron py rites, in containing a larger proportion of metal, to which, no doubt, its quality of being attracted by the magnet is owing.