Cornish Minerals of the Brochantite Group. 475 



I have met with a small and old specimen of Connellite with a twin 

 crystal of Langite associated with it. 



II. Waringtonite. 



To a Cornish mineral associated with Langite, emerald to verdigris- 

 green in colour, occurring in incrustations generally crystalline, and 

 seen occasionally in distinct individual crystals aggregated loosely on 

 the Killas, I have given the name of Waringtonite, in honour of my 

 friend Mr. Warington Smyth. The crystals are always of the same 

 form, that, namely, of a double- curved wedge. A narrow plane, 

 1, is very brilliant and without striation. It appears to be a 

 cleavage-plane. A second, but scarcely measurable plane, 10 0, 

 occurs at right angles to it, truncating the thin ends of the wedge. 

 The prism planes in the zones 10, 1, and 10, 10 are uni- 

 formly curved. The planes of two prisms seem to exist in the zone 

 1 0, 1, but the angles, as approximately measured by the gonio- 

 meter, are not very reliable ; one of them, however, may be pretty 

 confidently asserted to be very near 28° 30', which is the mean of 

 many measurements on four crystals. Seen in a microscope fitted 

 with an excellent eyepiece goniometer, planes of polarization in the 

 crystals are evidently parallel and perpendicular to the planes 10 0, 

 1; but whether a plane of polarization bisects the acute angle of 

 the wedge, i. e. is parallel to 1 or to 10 0, or whether 1 is 

 equally inclined to the planes forming the wedge — in short, whether 

 the crystal is oblique or prismatic, it is very difficult to determine. 

 The mineral frequently presents itself, moreover, in what appear to 

 be twinned forms ; but the angles between the planes 1 in the 

 two individuals are not sufficiently concordant, as measured on dif- 

 ferent crystals, to justify a speculation on the symbols of a twin face. 



Several analyses of Waringtonite concur in establishing its for- 

 mula as 3Cu"H' 2 2 -+-Cu" S0 4 + H' 2 0, as is seen by the following 

 numbers : — 



Percentage as Average 



calculated, found. 



4 equivs. copper = 126*72 = 53*99 54*48 



4 equivs. oxygen =32' = 13*63 (calc. 13*756) 



1 equiv. sulphuric anhydride = 40* = 17*04 16*73 



4 equivs. water =36* = 15*34 14*64 



234*72 =T00 T 0b 99*606 



It also contains traces of lime, magnesia, and iron, and appears 

 to be generally mixed with a small proportion of another mineral, 

 which is probably Brochantite, as Brochantite occurs in distinct crys- 

 tals on some of the specimens of Waringtonite. 



Its specific gravity is 3*39 to 3*47. 



Its hardness is 3 to 3*5, being harder than calcite, and about 

 equal in hardness to celestine. 



The entire difference of its crystallographic habit, the absence 

 of the striation and marked prismatic, forms so characteristic of 

 Brochantite, its habitually paler colour, lower specific gravity (in Bro- 



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