Cubical Sulphuret of Zinc, or Blend Enlarge
Feb.y 1. 1805. Publiſhed by Ja.s Sowerby. London.
British Mineralogy
CXII
Zincum sulphureum; Var. cubicum

Cubical Sulphuret of Zinc, or Blend

  • Class 3. Metals.
  • Order 1. Homogeneous.
  • Gen. 6. Zinc.
  • Spec. 2. Sulphuret of.
  • Div. Crystallized.

The rectangular cubical formation of these crystals of Blend is, I believe, quite new to the Mineralogical World. Two specimens have been sent from Cornwall, one marked from Tincroft, the other from Polgooth, and were probably from the stores of a miner who did not exactly know from what mine they were brought. These luckily came to the hands of my friend A. MacLeay, Esq., Secretary to the Linnean Society, who was so good as to give me the one here figured.

The cubes of this specimen curiously show the diagonal striæ, and indicate the accumulation of plates upon the tetraëdrons, or more common modification*. See these more plainly marked on the upper right hand geometrical figure.

The right hand figure shows these marks more faintly like the original with the marks of the fracture parallel to the edges—see the figure beneath, which, if carried regularly on every edge, would produce the rhomboidal dodecaëdron, one of the characters of the Bland. The gangue is mostly Copper Pyrites.

Since figuring this specimen I have met with a finer one from Cornwall with smaller distinct cubic crystals, or rather separate ones, much resembling Pyrites: the diagonal striæ however help to detect it, they are nearly gold-coloured, and iridescent externally, but dark like Blend within.

  • * It may not be amiss to remark that several other substances are striated in the direction of their principal modification; as Fluor, whose primitive is an octaëdron, but is generally striated in the direction of a cube; Oxide of Tin, &c. This arrangement of striæ is apt to mislead inexperienced observers.
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