190 



however being in any respect related to other silicates con- 

 taining niobium. It has a certain similarity to the minerals 

 of the clintonite group, but in most respects it is also very 

 different from these. 



Britholite, a new mineral, 



by Chr. Winther. 



This mineral, which G. Flink found in 1897 in the district 

 of Julianehaab, South Greenland, was provisionally called by 

 him «the cappelenitelike mineral» (Meddelelser om Grønland 

 XIV, 245). It is found in the locality of Naujakasik as small 

 brown, apparently hexagonal, prisms imbedded in the pegmatite 

 of the nephelite-syenite which is to be found there. 



The name has been formed from ßplöoc, weight, gravity 

 on account of the mineral's high specific gravity. 



Crystalline form. Several of the crystals are fully developed 

 at both ends and their exterior appearance is exactly like a 

 combination of the hexagonal prism {lOlo} and pyramid {lOU}, 

 sometimes with small faces of the prism of second series (ll20}. 



If the crystals are therefore considered as belonging to the 

 hexagonal system, they will have the axial ratio c = 0'732. 



However by further examination it is quickly found, that 

 this simple form is only apparent and that the crystals really 

 are polysynthetic crystals of rhombic single individuals, the 

 crystals having a somewhat similar form to that of the well- 

 known aragonite crystals from Aragonia. 



This was found from the fact, that the measurements of 

 the angles gave very different values for the edge angles and 

 it could be seen distinctly in the transverse sections, that every 

 crystal consisted of a number of united individuals of another 

 system of crystallization (optic biaxial). Experiments were 



