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way. It is thus sometimes seen, that thin layers of the epistolite 

 are imbedded in rinkite crystals parallel with their cleaving direc- 

 tion; there is therefore reason to believe, that these two minerals 

 have developed at the same time. The relation of the epistolite 

 to the polylithionite is even stranger; it is found inclosed in 

 the polylithionite, so, that it replaces greater or smaller parts 

 of it, and especially is it found very often in the center of the 

 large polylithionite rosettes , but it can also appear in isolated 

 parts towards the circumference. The cleaving directions of 

 both minerals run parallel and plates can be cleaved out, which 

 consist of both together; the limit between them is always very 

 irregular and there does not seem to be any crystallographic 

 uniformity as regards their position, the mutual direction of 

 {001} excepted. 



Chemical properties. According to an analysis , made by 

 cand. polyt. Chr. Christensen the epistolite has the following 

 composition: 



Quot. 



SiO^ 27-Ô9 0-460 



M2O5 33-56 0-126 



ГгО, 7-22 0-096 



FeO 0-20 0-003 



MnO 0-30 0-004 



CaO 0-77 0-014 



MgO 013 0-003 



Na,_0 . . , 17-69 0-284 



Щ0 11-01 0-612 



F 1-98 0-104 



Total . . . 100-35 

 Less oxygen-equivalent of the fluorine . . 0-83 



99-52 



Ta and Zr could not be traced in it; it contains a 

 minimum of K. 



