129 



The forms m and с are represented by even and brilliant 

 faces. The faces of the form d, on tlie other hand, present 

 the peculiarity of having only their marginal parts preserved 

 and somewhat brilliant, while the central portion has been sub- 

 ject to a decomposition process, which has occasionally gone 

 very far. The substance of the mineral has passed into a 

 brown powder which fills the cavity that has been formed. 

 Sometimes the decomposition has proceeded so far that only a 

 thin shell of the crystal remains. All the faces except those 

 belonging to the form d are still brilliant, but if such a crystal 

 is only gently pressed between the fingers, it will easily break, 

 and one finds that its interior consists only of the brown 

 powder. Such powder, which is often found in the mineral 

 druses on Narsarsuk, seems in other cases lo be the result 

 of the decomposition of other minerals, e. g. rhodochrosite. 

 (See page 30). 



IN'eptunite crystals of the third type have been found only 

 at the locality No. 7. Only a few specimens were met with, and 

 on them the mineral occurs very sparingly. The specim,ens 

 occurred lying loose among the gravel, and the underlying syenite 

 contained neither neptunite nor other minerals of the pegmatite. 

 As is usually the case, the specimens consist principally of 

 microcline and aegirine. The neptunite does not come into 

 immediate contact with the latter mineral, but the crystals 

 generally occur implanted on the microcline and are occasionally 

 surrounded with flexible laminae of polylithionite. Epididymite 

 occurs also here as an earlier formation than the neptunite, and 

 parisite as a later one. There further occur here a kind 

 of greenish grey columns , which evidently owe their origin to 

 the alteration of some other mineral. They have a serpentinous 

 appearance and seem to have formed from elpidite. 



The locality No. 7 is the only place where neptunite occurs 

 associated with narsarsukite, and this association is of a peculiar 

 character. Where the two minerals come into contact with each 

 XXIV. 9 



