171 



In relation to the coloration of ruby zinc, Dr. Hayes said that, 

 from" examination of tolerably pure specimens, he thought it due to 

 scales of transparent peroxide of iron, visible under the microscope ; 

 he did not find any red oxide of manganese in the mineral. 



Dr. C. T. Jackson said that, in the purest specimens, such as had 

 been submitted to jMi\ W. P. Blake's analysis, there was only a trace 

 of peroxide of iron, but an appreciable quantity of manganese. 

 This was the first specimen, pure enough for reliable analysis, a 

 crystal without any mechanical mixture. 



IVIr. Alger said that he had attributed the coloration to the oxide 

 of manganese, but should submit some of the pure crystals to Dr. 

 Hayes for further analysis. 



Mr. Alger exhibited a pseudomorpbic crystal of native 

 copper from Copper Falls Mine, Lake Superior. 



Who, he asked, has ever seen a crystal of native copper in the 

 form of a rhombohedron ? 



I ask this question in order to call your attention at once to the 

 subject in hand. 



It is well known to you that crystals of copper belong to the 

 monometric or regular system in crystallography, and are found in 

 nature in modifications derived from the cube or octohedron, fre- 

 quently, as in the trap rocks of Lake Superior, in perfect rhombic 

 dodecahedrons. Copper is not a dimorphous metal, that is, it is 

 never known to occur in forms incompatible with each other, or be- 

 lono-ino- to difierent systems, which we know is the case with some 

 other substances. For instance, bisulphuret of iron is found in the 

 form of a cube, and of a right rhombic prism ; carbon in the regular 

 octohedron (diamond), and in the regular hexahedral prism (graphite). 

 Carbonate of lime in the rhombohedron and right rhombic prism. 

 The specimen I now present is a rhombohedron of native copper, but 

 it offers nothing inconsistent with what has already been said, for it 

 is evidently the cast or impression of a crystal of calc-spar, which 

 has disappeared, and whose place it has taken with much precision. 

 I believe this is the first occurrence of a perfect pseudomorph of 

 copper in any form. I find no mention of any in the writings of 

 Haidinger or Blumm, who have written largely on the subject. I 

 found the specimen in examining a collection of specimens brought 

 from Copper Falls. It was partly incrusted by calc-spar in cleavable 

 crystals, indicating very clearly its pseudomorpbic origin. On re- 

 moving this calc-spar I found, presented on the opposite side of the 

 specimen, a fine example of arborescent or dendritic copper, giving 

 it rather a remarkable character. 



In reply to Dr. Jackson, who thought the crystal might be a cube, 

 a form which copper might naturally assume, Mr. Alger said that the 



