1865.] of the Brochantite Group. 399 



smooth surface of porcelain or chalcedony, it leaves the celestine without 

 perceptible abrasion. Brochantite, on the other hand, deeply cuts into 

 that mineral. 



In comparing the physical characters of these two minerals, one has fur- 

 thermore to observe that, besides their differences in hardness and specific 

 gravity (in Brochantite G=3-87-3'9), their crystallographic habits are 

 entirely dissimilar. Thus if we assume, for comparison's sake, the angle 

 obtained for the normal inclination of the planes 1 1 0, 1 1 in Warington- 

 ite to correspond to that between e e or 1 I, Fo 1 of Brooke and Miller 

 in Broclmntite, a point of view from which we see the two minerals in the 

 most advantageous orientation for comparison, we shall find that the planes 

 of the form (1 1) in Brochantite, like those of (1 1 0) in Waringtonite, are 

 much curved ; the plane I 0, however, is a well-marked plane in Brochan- 

 tite, striated parallel to the zone-axis [0 1J. In Waringtonite the corre- 

 sponding plane, 1 0, is a curved surface without striation. The plane 001 

 is furthermore a most conspicuous plane in the latter mineral, while the 

 analogous plane I in Brochantite is, I believe, unknown. 



A mineral, described by Berthier (Ann. Chim. Phys. 1. 360), and one 

 recently analyzed by Domeyko (Annales des Mines, 1864, p. 460), gave the 

 following percentage composition : 



Berthier. Domeyko. M. Pisani. Waringtonite. 



Copper 52-85 55'89 54-9 54-48 



Oxygen 13-35 14-15 13'9 13*756 



Sulphuric anhydride .. 16-6 16-15 17'2 1673 



Water .. . 17'2 13-81 13-2 14-64 



100-0 100-00 1-0 99-606 



CaO -8 



101-0 



In the third column of the above Table I have also given the results of 

 M. Pisani's analysis of a green mineral which he found associated with Lan- 

 gite, and which was probably Waringtonite mixed with the ferruginous 

 Kilias (on which it often occurs). He assigned the mineral to Brochantite. 

 Berthier' s mineral from Mexico was probably Waringtonite containing 

 hygrometric moisture, as by deducting two per cent, of water his analysis 

 almost exactly accords with the numbers representing that mineral. The 

 green fibrous mineral from the Cobre mines in the Atacama desert would 

 seem, from the description of the eminent mineralogist of Chili, to be a 

 mixed substance. 



III. Atacamite. 



I have mentioned that the first specimen of Langite that came into my 

 hands had upon it small bright green crystals of a mineral with the angles 

 of Atacamite. These angles were the following : 



