Arseniate of Copper

Mr. Rashleigh, with his usual ardour for the promotion of science, sent me the present specimen of Arseniate of Copper. It has the appearance of cubic crystals of Arseniate of Iron on the apex or ends of the radii of Wood Copper. However, a good crystallographer may find out the real conformation; and as it is truly curious and instructive, we were pleased to have such a specimen come under our inspection, that it may be understood hereafter. The two preceding Tables show the nature of this modification, and it is only a series of radiating, or partly radiating crystals, which crowd together wedge-like, as happens with calcareous Spar, terminating with octaedrons so crowded as to show in general only as much as resembles the sides of a cube placed obliquely with the edge upwards: see the left hand figure. The other outlines show how it accords with the modification of the preceding figures.

There is a tendency to a concave formation of the faces which belongs to this cctaedron, and often may be seen in cubes of Arseniate of Iron, tab. 87: it in some measure aids the deception. The Arseniate of Iron is generally of a yellow-green.

The Arseniate of Copper in these three tables rests upon Quartz in part crystallized, but chiefly in broken fragments mixed with Oxide of Iron.