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been mentioned above, between the two kinds of steenstrupite, 

 may be in some cases directly observed at total reflection. 

 However the two parts are as a rule quite similar in color 

 and it is not possible to trace pleocroism in the double 

 refracting part. The proportions, in which the above mentioned 

 interpositions stand to the phenomena of double refraction, are 

 quite characteristic. The tongues protruding from the dark 

 edge are without exception surrounded by the strongest double 

 refracting parts ; even if the limit of these parts otherwise runs 

 quite straight it may be seen bending down like an arch round 

 such an apofyse. The strong brown parts are however not very 

 double refracting themselves. The very small black interposi- 

 tions sometimes transgress unaltered from the one part to the 

 other; but in some cases they keep almost exclusively to the 

 single refracting parts, which on account of this become some- 

 what darker than the others. As regards the crystals of type 1, 

 those from Naujakasik and Tupersiatsiap have still in most cases 

 a thinner margin, which is rather strongly double refracting, 

 while the crystals from Kangerdluarsuk almost always are very 

 insignificantly double refracting right through. However here 

 also a somewhat stronger double refracting part may be found, 

 either at the surface or in any case only separated from it by 

 the above mentioned brown part. 



Ocairrence. The steenstrupite occurs almost always as 

 small loose crystals, scattered amongst the other minerals and 

 it is older than the greater number of these. In the localities 

 North of the Firth of Tunugdliarfik it occurs chiefly in snow- 

 white grained albite together with other forms of feldspar, 

 aegyrile, pseudomorphosed hornblende prisms, sphalerite, soda- 

 lite and several minerals, among which the new ones called 

 schizolite by Winther and epistolite by the author especially 

 occur in greater quantities. The steenstrupite is older than all 

 these minerals , except aegyrite and the epistolite , which at 

 XXIV. 14 



