Arseniate of Copper

This being, I suppose, a scarce variety, not having been mentioned by the experienced Count Bournon, I am happy to give a figure of it to the public. Among the clusters of grass-green crystals of arseniate of copper, we mostly find some with the corner of the mutual base of the pyramids more or less rounded. These in the present specimen form regular facets, making it a twelve-sided crystal. The facets pass the common base at right angles, cutting off the four corners: theus the mutual base is an octaëdral plane, at right angles with the four corners of the double pyramids.

They are somewhat uneven, and show evident signs of the want of a few molecules to fill up their interstices. The crystals in general seem to have been disturbed or interrupted, and show markings on their surfaces. Besides this, I have a variety with the sides of the mutual base somewhat rounding, though scarcely perceptible, which is figured in the left hand outline. The broken crystal in the middle, to show the blue within, was most conspicuously so, and is figured of its natural size, being larger than usual: the other two are slightly magnified. We have since met with one five-eighths of an inch long.