Curving or Bending Pyrites
- Div. 2. Imitative.
Perhaps I could not show any thing more extraordinary or, I believe, more rare in the system of Crystallization, than the present specimen which I possess by favour of my good friend Philip Rashleigh, Esq., of Menabilly, who sent it to me in 1806, labelled from Car uncial e in Devonshire.
Pyrites is well known to form the Cube and Octaëdron, with their modifications, very neatly: sec tabs. 29, 30, 99, &c, and to produce varieties from them, wedge-formed, rounding, concave, and convex, cock’s-comb-like, &c.; see tabs. 366 and 367; and to mix in somewhat cruciform and other odd appearances. In the present instance the Pyrites seems more like Sheet Metal cut into pieces, as if with a pair of sheers, curving in various directions: thus we have an appellation of “imitative” to recognise it by; which is very convenient in the present instance. I do not know that curved crystallization has been at all mentioned by any author. I should suppose, however, that it depends upon the same laws of aggregation in this substance as the straight or rounded; see vol. ii. p. 57: and the rounded figure in tab. 131. Its state while depositing from the solvent, and the solvent, may account for immense variety. This, however, is a very rare example, identifying a new kind of form, and bespeaking another source of boundless variety. The crystals seem to be formed of plates belonging to the cube and cubo-oetaëdron, passing in a more or less continued line of elongation, forming a sort of wall-like appearance in various directions, and may perhaps be compared to a tall weak wall on an irregular foundation, bending before it was hardened by drying. The crystallization of Pearl-spar, tab. 19, lower figure, which curves, seems governed by a different law: the molecules seem to slip while depositing; and the Sulphate of Lime, tab. 68, seems to bend from an elastic property.