OF THE JEFFERSONITE. 197 



instance, cleavages parallel to a rhomboidal prism of 

 116° and 61°. I have also obtained cleavages under an 

 angle of about 99° 45' and 80° 15'. I have not been 

 able to trace the connexion between these and the 

 former, but I am inclined to think, that they result 

 from the combination of the two prisms just mention- 

 ed. 1 had hoped, as some of the cleavages have a 

 tolerable degree of lustre, to have been enabled to de- 

 termine the angles by the reflecting goniometer, but 

 all my attempts to that effect have proved unsuccess- 

 ful. I have not been able to obtain a reflection from 

 any one face. 



The hardness of this mineral is intern ediate be- 

 tween that of Fluor Spar and Apatite. It is very 

 readily scratched by Pyroxene, (Malacolite.) 



Its specific gravity varies from 3. 51 to 3. 55. I 

 have in one instance obtained it as high as 3. 64, but 

 I suspect the mineral to have been mixed with Frank- 

 linite. 



Its colour is dark olive-green, passing into brown. 



It is slightly translucent upon the edges. 



Its lustre is slight, but semi- metallic upon the faces 

 of cleavage ; in the transverse fracture it is resinous. 



The fracture is lamellar when in the direction of 

 cleavage, otherwise it is uneven. 



When scratched with a knife, the streak is gray- 

 ish. 



The colour of the powder is a light-green. 



Before the blowpipe it melts readily into a dark 

 coloured globule. 



