44- 



proceeds to describe the external appearance of the specimens he 

 has had opportunities to examine; and from these characters, to- 

 gether with an accurate analysis of the different sorts made by 

 Mr. Chenevix, he deduces the following classification of this new 

 mineral. 



The principal distinction is in arseniates of copper and of iron. 

 Of the former there are four species : 



1. Arseniates of copper, in the form of an obtuse octaedron. This 

 is said to be the most simple, and appears to be the original form of 

 an ore. The minute descriptions of the crystals are in this, as in all 

 other species, illustrated by delineations. This sort is very light, its 

 average specific gravity being 28'819. Its hardness is inconsiderable, 

 and its transparency seldom perfect. Its colour is either a beautiful 

 deep blue or a fine grass-green, and sometimes white with a slight 

 blue cast. According to the analysis, this variety of colours depends 

 chiefly on the quantity of water which enters into the crystallization. 



2. Arseniate of copper in hexaedral laminae with inclined edges. 

 The colour of this ore is a fine deep emerald green, and sometimes a 

 light green. Two of the six sides have so great a lustre that they 

 often assume the appearance of metallic foils. Its specific gravity is 

 25-488. It is less hard than the preceding species. Its thin crystals 

 are transparent, and it frequently decrepitates in fire. 



3. Arseniate of copper in the form of acute octaedrons. Its colour 

 is a brown or bottle-green, the surface often reflecting a golden tint. 

 Its specific gravity is 42*809. It is sufficiently hard to scratch fluor 

 spar, but not glass. Its transparency is generally very great. These 

 general characters are by no means permanent. Its crystals are not 

 always determined, nor does it at all times exhibit a similarity of 

 colours. These differences of form and aspect have induced the 

 Count to distinguish five varieties, which are denominated as follows: 

 1. Capillary of a determinate form ; 2. Capillary of an indetermi- 

 nate form; 3. In crystals perfectly regular in one part of their 

 lengths, and fibrous at their extremity ; 4. Amianthiform, consisting 

 of very delicate flexible fibres ; and 5. Hematitiform, not unlike the 

 tin ore known by the name Wood-tin. 



4. Arseniate of copper in the form of a triedral prism. As the 

 crystals of this species are seldom sufficiently insulated to be distinctly 

 perceivable, and are in general so small as to escape the naked eye, 

 all their various forms are here more particularly described, and also 

 their progressive change of figure as they deviate from their primitive 

 configuration. Its specific gravity is 42'809. Its hardness is not so 

 great as that of the preceding species, as it does not easily scratch 

 calcareous spar. Its crystals are often transparent, and of a very 

 beautiful blueish-green colour ; but their surface easily decomposes, 

 and the crystals then become black and perfectly opaque. 



The second class, being the arseniates of iron, is distinguished into 

 two species : 



1 . The arseniates of iron, properly so called. This ore crystallizes 

 in perfect cubes, sometimes, though rarely, a little flattened. Its 



