TAB. XXXII. 



CUPRUM arseniatum. 

 Arseniate of Copper. 



Class 3. Metals. Order I. Homogeneous. 

 Gen. 4. Copper, gpec.'g. Arseniate of Copper. 

 Div. 1. Crystallized. 



Far. The solid angles of the mutual base of the two pyramids 

 truncated. 



Spec. Char. Arsenic acid combined with copper. 

 Syn. Phil. Trans, for 1801, p. 169. 



I his 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 : thus the mutual base is an octaedral 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 in- 

 terrupted, 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. 



