40 Prof. Maskelync and Dr. Lang's Miner alogical Notes. 



by Mr. Williams to have been unopened for fifty years. With 

 the specimens were a few original labels, which exhibited, how- 

 ever, only two kinds of inscription, viz. " Arseniate of copper, 

 Huel Unity," and " Arseniate of copper, Huel Damsel." It 

 was Professor Connell, after whom this mineral is deservedly 

 named, who first proved its old designation as an arseniate of 

 copper, to be erroneous. Messrs. Lettsom and Greg, in their 

 ' Manual of British Mineralogy/ mention Huel Providence and 

 Carharrack as reputed localities of this mineral. The latter 

 locality, from its proximity to the old Huel Unity (both mines 

 being now merged in what was till lately called the St. Day 

 United Mines), has not improbably been a source of it ; but the 

 claim of Huel Providence to the production of Connellite is 

 problematical. 



The crystals of this mineral are extremely minute, the largest 

 not possessing dimensions greater than -r^th of an inch in 

 thickness and about -M;h of an inch in length. I have found 

 one with both terminations perfect, but of considerably smaller 

 dimensions than the above. The crystals belong to the hexa- 

 gonal system, and exhibit a hexagonal pyramid formed of the 

 two rhombohedra 100 and 12 2, sometimes terminating the 

 regular hexagonal prism (101); but more usually associated 

 also with scalenohedra, the one of which is the inverse of the 

 other, and the second hexagonal prism (211) truncating the 

 edges of the first. 



In crystals so minute, of which one presents as many as forty- 

 eight planes on an area represented by the dimensions above 

 given, it would be almost impossible to obtain measurements of 

 any value by the ordinary reflecting goniometer. 



But by means of a small plano-convex lens in front of a small 

 telescope with a magnifying power of about nine times attached to 

 the goniometer, and which converts that telescope into a sort of 

 microscope of low power, it is not difficult to obtain measurements 

 of considerable exactitude. The adjustment is aided by screw 

 motions ; and it is requisite to diminish the size of the aperture 

 for the light as much as is consistent with the adequate illumina- 

 tion of the planes. When the faces are minute, and present a 

 plane surface and lustre, the method is exact enough. But 

 where the planes are curved, as is the case with the scaleno- 

 hedra of Connellite, very accurate measurement is impossible. 



The angles obtained from the more perfect planes of this 

 mineral agree with an angular element of (1 0) (11 1) =53° 10 f . 



The planes on the crystal are 



