48 



with the ilvaite, may perhaps give some ekicidation with regard 

 to this fact. 



I. Ilvaite from the Sodalite-syenite. 



All the largest eastern part of the locality of the ilvaite is 

 occupied by transformed sodalite-syenite with interjacent layers 

 and lenses of lujavrite. In the latter rock no crystals of ilvaite 

 have been found ; only in the most transformed parts the ori- 

 ginally present dark minerals, especially the arfvedsonite, have 

 been turned into dense ilvaite. With regard to the sodalite- 

 syenite, no crystals of ilvaite have been found outside of the 

 veins of pegmatite. The rock itself has been subjected to a 

 rather considerable transformation. The only mineral that has 

 remained unaltered, is the feldspar; it has still everywhere the 

 same characteristic microcline-micropertite-like structure, as has 

 been described by N. V. Ussing^), but the colour, in stead of 

 the original grayish one, has passed into reddish-white. The 

 sodalite which is so characteristic of the structure of the rock, 

 being found as small crystals scattered rather evenly among all 

 the other ingredients, has become a fine-grained mixture of 

 almost microscopic grains of a whitish mineral, probably a 

 variety of feldspar intermixed with small green crystals of epi- 

 dote. The nepheline and eudialyte have been subjected to 

 about the same transformation. The dark minerals, the arfved- 

 sonite and aegirite, have been transformed into a greenish, 

 single-refracting mass, in which sometimes small amounts of 

 ilvaite may be disengaged. 



The vein^of pegmatite in the sodalite-syenite, on the other 

 hand, have been much more thoroughly transformed. The feld- 

 spar has still partly been preserved as microcline-micropertite, 

 and has also here assumed a reddish white colour. But part 



Mineralogisk-petrografiske Undersøgelser af grønlandske Nefelinsyeniter. 

 The present journal XIV. 



