115 



seem to be closely allied to microlite, which contains only pen- 

 tavalent acids. 



The other group comprises all the other minerals from 

 the table ; they are almost all of them rhombic, and even if 

 they cannot be said to be what is properly called isomorphous, 

 great correspondence may nevertheless be pointed out between 

 their axial ratios, in which respect a few of them approach 

 very much to columbite. The individual minerals belonging to 

 other crystalline systems, are the four ones, steenstrupite, 

 wöhlerite, epistolite, and dysanalyte. Of these wöhlerite being 

 monoclinic, approaches the rhombic minerals rather much in 

 its crystallographic elements; dysanalyte sometimes contains 

 so small quantities of pentavalent acids, that it can scarcely be 

 classed with the minerals treated here; it crystallizes isometric 

 in cubes, and is in most respects closely allied to perovskite. 

 Steenstrupite, which is rhombohedric, contains in all cases 

 only small quantities of pentavalent acids, in the somewhat 

 transformed varieties even very small quantities ; by its che- 

 mical composition it is very closely allied to melanocerite and 

 karyocerite, which minerals are also rhombohedric without, how- 

 ever, being isomorphous with steenstrupite; on the other hand, 

 this mineral is isomorphous with eudialyte, with which mineral 

 it does not seem to be closely connected with regard to che- 

 mical composition. The epistolite is monoclinic, and as far as 

 can be shown it is not isomorphous with any other mineral; 

 also by its other physical qualities it is very distant from the 

 other minerals treated of here, they being all dark, hard, and 

 with rather great specific weight, while the epistolite has some 

 outer resemblance with the minerals of the clintonite-group, 

 without, however, agreeing with those in some of the most 

 essential features. As far as I am able to see the epistolite, 

 both with regard to its chemical and physical qualities , is 

 without any nearer relation within the mineral kingdom. 



Among the rhombic minerals only two, viz. euxenite and 



