1865.] of the Brochantite Group. 397 



angle of the prism 1 1 0, fl = 5634', TOO (I 1 0) 1 C = 124 10' 

 (calculation requires 123 44'). 



II. Waringtonite. 



The mineral to -which I would next invite attention is one with a colour 

 varying from emerald to verdigris-green that occurs sometimes mixed with 

 Langite, but more often forming with it a continuous coating on the Killas 

 or vein-stone, one part of this coating being in such cases Langite, and 

 another part of it consisting of the mineral in question. At first I was in 

 doubt whether this green body was not the result of the action of heat on 

 Langite in fact a pseudomorph after that mineral. 



Subsequently, however, Mr. Tailing sent me some unmistakeably crys- 

 talline specimens, and as at that time I had already made its analysis, there 

 could no longer be any doubt that it was a new mineral. 



I propose to call it " Waringtonite " in honour of my friend Mr. Waring- 

 ton Smyth, Inspector of Mines to the Crown Lands, and to the Duchy of 

 Cornwall, &c. 



The crystallography of Waringtonite presents a difficult problem, for the 

 reason that it carries only one very distinct plane. The prevalent form of 

 the crystals, which are almost microscopic, is that of a double curved 

 wedge (or, to use a familiar illustration, like a stonemason's double- 

 edged hammer), the flat summit being formed by this distinct but narrow 

 plane. That plane is characterized by great brilliancy, is bounded by 

 curved outlines, and though often fissured near its extremities by the accu- 

 mulation of two or more parallel crystals in optical contact at their centres, 

 is otherwise without striation. If we call this plane, by its analogy to the 

 brilliant and unstriated plain in Langite, 001, and refer a very minute 

 plane occasionally seen on the acute edges of the wedge to the form I 0, 

 we find the planes 1 0, 1 0, and those in the zone [0 1 0, 1] repre- 

 sented by rounded surfaces, from which it is impossible to obtain any accu- 

 rate measurements ; and the prism planes in the zone [1 0, 1 0] are 

 likewise much curved. There would seem to be two prisms in that zone, 

 one of which forms a normal angle approximately determined as 

 1 1 0, T 1 = 28 30' very nearly. 



It is difficult to say whether \Varingtonite is prismatic or oblique. The 

 plane 1 forms an angle of 90 with those in the zone [0 10, 100]; and the 

 principal planes indicated by the planes of polarization, as seen on looking 

 down the normal to 1 0, are parallel to 1 and 001; but it is very 

 difficult to speak with certainty as to the exact directions of the planes 

 of polarization as seen when looking through the plane 001, and as to the 

 direction of a plane of polarization really bisecting the acute angles of the 

 wedge. 



The crystals often occur in interpenetrating forms, with the appearance 

 of being twins. 



The angles, however, between corresponding planes in the two indivi- 

 duals are not sufficiently uniform for the establishment of a twin plane. 



