318 



Crystal of JVative Copper. 



DESCRIPTION OF A CRYSTAL OF NATIVE COPPER, 

 In the Cabinet of CoLoifEi. Abeet, at Washington. 



The primitive form of crystals of native copper, is stated to be 

 a cube. The form of the crystal in question is that of a cube, 

 with all its solid angles replaced by triangular planes. 



The decrement of the solid angles by the triangular planes, is 

 extended, until the angles of the triangular planes meet at the 

 centres of the edges of the faces of the primary cube, forming a 

 regular figure of six square faces, and eight triangular faces, 

 the square faces being also the faces of the primary cube. 



Measurement does not prove either face to be a perfect square, 

 or a perfect equilateral triangle ; the differences from such figures 

 are, however, very slight, and occasioned in some of the faces, by, 

 evidently, artificial indentations of some of the angular f)oints. 



Several of the faces have slight incrustations of carbonate of 

 copper upon them, and all of them have striag, which have 

 been considered by some who have seen the crystals, as marks 

 of a file, used to free the crystal from the crust in which it was 

 enveloped, when first found. But I have not considered them as 

 resulting from such a cause. They are irregular in depth, width, 

 and length, not always parallel, are strongest near the edges of 

 each face, — the middle of several of the faces being entirely free 

 from them. The colour of the striae, also indicates an exposure 

 equal to that of any part of the crystal. 



The edges of the square faces are, of course, varied from the 

 position of the edges of the primary cube, and are now parallel 

 to what w^ould have been a diagonal of a primary face ,* and the 

 square faces are smaller, by the extent of the decrement. 



Mr. J. P. W. and Dr. M. of Philadelphia, were both disposed 

 to consider it a genuine crystal of native copper. 



I am not quite sure of its history, and am now endeavouring 

 to trace it out, but believe it came from South America. It was 

 among coppers from that quarter, from England, from Siberia, 

 and from Germany ; and if any label had ever been aflixed to it, 

 noting its history, it has been rubbed off. 



The doubts which have been raised in relation to this crystal's 

 being a natural formation, are founded upon its unusual size. 



Taking the faces of the cube by pairs, the following are its 

 dimensions, or the direct distances between each pair of faces : 



