49 



of it has been turned into a fine-grained aggregate of albite, 

 possibly with other varieties of feldspar that have not yet been 

 more closely examined. The eudialyte, nepheline, and sodalite 

 are no longer to be traced; these minerals are perhaps merged 

 in the same fine-grained mass. The only one of the more rarely 

 tound minerals that has been traceable, is the steenstrupine, 

 which has been found in one of the pieces brought home, as 

 a pseudomorph containing a white, fine-grained mass. The 

 dark minerals, the arfvedsonite and aegirite, have entirely dis- 

 appeared; the place formerly occupied by those minerals, is 

 sometimes quite taken up by dense ilvaite; but more frequently 

 a cavity has been formed, the walls of which are covered by 

 crystals of ilvaite and albite , on which crystals microscopic 

 crystals of epidote may sometimes be found, or more rarely 

 small, clear dodecahedra of a green garnet. These cavities may 

 often plainly have the form of prisms of arfvedsonite; but in 

 many cases all traces of a regular outer form have disappeared, 

 and then it is not to be decided whether the cavity has origin- 

 ated in the way described above, or perhaps has been found 

 originally in the pegmatite; the former is likely to be the case, 

 if the larger part ot the crystals in the cavity or all of them 

 are formed of ilvaite. 



Besides the minerals mentioned above which are the most 

 constant companions of the ilvaite, some others occur in the 

 transformed veins of pegmatite. A peculiar position is held by 

 the haematite; it is found as small, black or shining red, ro- 

 settes, and appears in some cavities to replace the ilvaite, but 

 is far more rare than this latter. These two minerals have 

 only in one case been found intermingled, otherwise the pre- 

 sence of one completely excludes the other. 



Still is to be noted the calcite which plays a prominent 



part on account of the influence that it appears to exercise on 



the form of the ilvaite. It is always found as a complete filling 



up of the cavity between the crystals mentioned above, and 



XXV. 4 



