Sulphuret of Antimony

Sulphuret of Antimony has been found in Great Britain only in acicular crystals or foliated masses; in other countries it frequently occurs in large groups of well-defined crystals, such as that now figured, probably from Auvergne, which is lent me by my friend, Mr. Plasted. The lesser figures are intended to represent the plumose variety, or that in minute down-like fibres, and the Iridescent scopiform one. The former is among loose minute crystals of Quartz, upon Sulphate of Barytes; both are from Hungary.

The primitive form of this ore is by Haüy supposed to be an octohedron, divisible by three planes, which united together, would form a rectangular prism; the fractures parallel to this octohedron are very deficient in neatness and lustre, while two of the three that form the prism are tolerably well distinguished, and the third presents a surface equal to the most perfect mirror, and is very easily obtained in the longitudinal direction of the crystals; it is with good reason, therefore, that Bournon has adopted this prism for the nucleus, independently of its being the simplest form; the proportions of the terminal faces to the height of the prism, has been determined by Bonrnon, to be as the numbers 24, 16.8, and 21. The pliability of this substance, first observed by Bournon, is analogous to that of crystallized Sulphate of Lime, and probably, like it, depends upon the proportions of the sides of the nuclei to each other.

I have given outlines of two crystals from the large specimen, and of a third out of a specimen from Wolfsberg, in the Hartz, by favour of Professor Herrmann: the latter is a rare modification to find complete; the commencement of it is shewn in one of the others.

The grouping of the crystals in the large specimen is rather whimsical; one small one in particular lying across the summit of another has been bent, and seems so placed on purpose to exhibit the character of pliability.