OF THE JEFFERSONITE. 203 



tirely, and be replaced by cleavages parallel to se- 

 condary crystals. On the contrary, wherever mine- 

 rals have been found presenting different orders of 

 cleavage, the first or those parallel to the primitive 

 form were always predominant. Thus in Carbonate 

 of Lime, it is not uncommou to meet the cleavage pa- 

 rallel to the equiaxe, but 1 believe in every instance 

 the primitive is predominant. In a rarer and more 

 interesting instance, that of Fluor Spar, Professor 

 Mohs has described, and I have seen in his posses- 

 sion in Freyberg, specimens of the Saxon Fluor 

 which cleaved in the direction of the cube and the 

 dodecahedron, but the octahedral cleavage was very 

 distinct. Before we change our opinion on this point, 

 we must change all our ideas of cleavage, and of its 

 high importance in the determination of minerals. 



In the hardness there is also a remarkable differ- 

 ence, the Pyroxene being decidedly harder. The 

 specific gravity is likewise different: the highest spe- 

 cific gravity of Pyroxene recorded by Haiiy, is that 

 of a large crystal from Vesuvius, which gave 3.3578. 

 The highest specific gravity indicated by Mohs is 

 3.5, while that of the Jeffersonite has, in every in- 

 stance which I have seen, exceeded this limit. 



The chemical analysis offers another important 

 difference, in the absence of magnesia, which ap- 

 pears to be essential to Pyroxene. 



For these and other reasons, I conceive that there 

 can be no doubt as to the necessity of considering 

 this mineral as a distinct species. I am inclined to 

 believe that a closer study of the Diopside and Fas- 



