Sulphuret of Iron, Pyrites

This form seems to belong to the cubo-pentagonal dodecaëdron, and the substance is rarely found not to partake somewhat of the modification that indicates it. See the last plate. The upper figure in this plate has the edges of those faces as much obliterated by rounding as any I have seen, and is nearly a congeries of minute striated cubes, some of which are tolerably distinct about it. It is from Cornwall. Crystals of this substance are occasionally found at different places, detached, and are flattish like the middle figure, or square and somewhat grouped like the right hand figure, or solitary and very regular like the other figure. Rounder specimens are not unfrequent, in which numerous other figures are formed into a round bundle, either octaëdrons, cubes, or cubo-oetaëdrons, &c.; but that seems to depend upon some other laws, and is as it were a pile of crystals. There are also some that are formed in plates, not much unlike Sulphate of Barytes or Cawk of the miners. See tab. 96.