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lowermost geometrical Jgure, or have the above-mentioned 

 three faces terminating in a point like the dotted faces on the 

 distant side, or with another triangular face like the light or 

 left hand sides of the same Jigure. The truncation of the 

 four solid angles, in the left hand and the geometrical Jigure, 

 are parallel to the octaedron. These modifications are all 

 evident in the present specimen, which is a Cornish one. 

 They rest on a greenish chlorite, on a light sort of schist 

 or slaty rock, commonly called killas by the Cornish miners. 

 They are often accompanied with rock crystals and copper 

 pyrites. The nucleus is a rhomboidal dodecaedron, and 

 the integrant molecule is a tetraedron with isosceles trian- 

 gular faces, according to Haiiy. The modification called 

 encadre by that author, among his sulphurets of copper, 

 resembles this very muchj but he does not seem to have 

 known such in sulphuret of zinc. Its specific gravity 

 is 4-1665 according to Brisson, It may be scratched with 

 a knife, and it will scratch sulphate of barytes, but not fluor. 

 Refraction simple, Hauy. 



