88 Prof. Maskelyne On New Cornish Minerals. [Feb. 23, 



II. Waringtonite. 



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

 in colour, occurring in incrustations generally crystalline, and seen occa- 

 sionally in distinct individual crystals aggregated loosely on the Killas, I 

 have given the name of Waringtonite, in honour of my friend Mr. Waring- 

 ton Smyth. The crystals are always of the same form, that, namely, of a 

 double-curved wedge. A narrow plane, 001, is very brilliant and without 

 striation. It appears to be a cleavage-plane. A second, but scarcely 

 measurable plane, 100, occurs at right angles to it, truncating the thin 

 ends of the wedge. The prism planes in the zones 010, 001, and 010, 

 100 are uniformly curved. The planes of two prisms seem to exist in the 

 zone 010, 001, but the angles, as approximately measured by the gonio- 

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

 fidently asserted to be very near 28 30', which is the mean of many 

 measurements on four crystals. Seen in a microscope fitted with an excel- 

 lent eyepiece goniometer, planes of polarization in the crystals are evi- 

 dently parallel and perpendicular to the planes 100, 001; but whether a 

 plane of polarization bisects the acute angle of the wedge, i. e. is parallel to 



1 or to 1 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 different crystals, to justify a speculation on the symbols of a twin face. 



Several analyses of Waringtonite concur in establishing its formula as 

 3Cu"H' 2 2 + Cu" SO 4 +H' 2 O, as is seen by the following numbers : 



234-72 =100-00 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 pro- 

 bably Brochantite, as Brochantite occurs in distinct crystals 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 BrochantiteG=3'87 to3'9), 

 and hardness sufficiently distinguish it from that mineral. The moun- 

 tain-green streak offers an available means of contrasting Waringtonite 



