Pyrites

in mineralogy, a name first given by ancient mineralogists to the native sulphuret of iron, because, when struck against a ‘piece of steel or other hard body, it gives out sparks of fire; and when heated red-hot, the sulphur that it contains burns with a lambent blue flame. It occurs ma ive, and free quently crystallized: the forms of its crystals are various, but the most common is the cube regular, or modified by truncation of the angles or edges, or acumination of three planes on the angles’: the octaedron, dodecaedron, and icosaedron, also sometimes occur. Its colour is bra -yellow, varying a little in the shade, and the lustre is always fully metallic: it is opaque. The fracture is uneven. It is brittle; its hardne is.such as to strike fire with steel; its specific gravity is from 4.6 te 4.8. By friction it exhales a sulphureous smell. This odour is strong when it is heated before the blow-pipe; it gives at the same timea blue flame; and at length a globule of a brownish colour, Itis soluble in nitric acid, with the, disengagement of red vapours. It is not sensibly magnetic. Various analyses of it have been given: according to those executed by Mr. Hatchet, it consists of Sulphur-ceeseee receee dB Tron -00je ceccpec vechd eee Besides this variety, which may be named common pyrites, there are some others which differ principally in structure, or in the form under which they occur. The striated or radiated pyrites presents a striated fracture, the striz being generally diverging. It is rather more liable to tarnish than the receding, and decomposes more readily in a Camel atmosphere. According to Mr. Hatchet's analysis, it consists of Sulphur +++eseseeees 0054 Tron.eerceecscece oan) eee The capillary pyrites occurs in delicate capillary crystals, grouped, parallel, diverging, or interwoven, slightly flexible, having a metallic lustre, and a colour pa ing from yellow to steel-grey. There is, lastly, the hepatic pyrites, so named from the liver-brown colour, which it a umes from exposure to the air. In the fresh fracture its colour is pale bra -yellow, inclining to steel-prey. It eccurs ma ive, of various imitative forms, and crystallized in six-sided prisms, or six-sided pyramids; it has le lustre than the others, and is more subject to decomposition. What has been named magnetic pyrites, distinguished, as the name implies, by its magnetic quality, of which the others are destitute, has been considered as forming a distinct species. Its colour is deeper, being intermediate between bra -yellow and copper-red, and approaching even to brown, often tarnished: its lustre is.also inferior, but is still metallic. © It occurs only ma ive or di eminated. Its fracture is compact: it is hard and brittle: its specific gravity is 4.5. It appears from Mr. Hatchet’s analysis of it to differ from the other iron pyrites, in containing a larger proportion of metal, to which, no doubt, its quality of being attracted by the magnet is owing. Besides the ferruginous pyrites, modern mineralogists distinguish two other species, the cupreous and the arsenical, the former of which is a sulphuret of copper, and the latter a ‘compound of ferruginous pyrites and arsenic. All, however, have a general resemblance in. their external appearance, the colour varying in each of them from a yellowish white to a aie yellow; and they have all a high metallic usire. 854