163 
is later than the sodalitization. In many cases an inner core 
of the original nepheline has remained unaltered, but instances 
of complete alteration are also very common. The analcime 
shows the same characters as that replacing the felspars. As 
a rule the nepheline is more altered than the felspar: in such 
specimens where only a small amount of nepheline has been 
converted into analcime the felspar is intact. — Another com- 
mon alteration of the nepheline is that into radiating zeolitic 
aggregates known by the name of spreustein !. This alteration- 
process is later than the formation of analcime; in several 
specimens it has affected the entire quantity of nepheline which 
has escaped the conversion into analcime. The nepheline-spreu- 
stein as a rule consists of hydronephelite as shown by the 
optical characters of the mineral; it is uniaxial with positive 
double refraction. In a few cases, however, nepheline-pseudo- 
morphs nf a somewhat different appearance have been observed 
which upon optical examination prove to be natrolite. 
Eudialyte is present in varying amount and in some spe- 
cimens it is abundant. И is in idiomorphic crystals of the 
ordinary form, ‘/2 or 1 millimeter broad. Occasionally, minute 
prisms of arfvedsonite and ægirine are found as inclusions. In 
hand-specimens the colour is brown, never red, and in thin 
sections it is clear and colourless or slightly brownish. Ве- 
tween crossed nicols a zonary banding is sometimes seen. The 
birefringence is often abnormally low; as a rule it is positive, 
but the outer zone of the crystals sometimes show a very low 
negative birefringence, and irregular patches of the same char- 
acter may be found along the cracks. Occasionally small dis- 
placements along the latter indicate that the crystals have been 
slightly acted upon by mechanical forces. — In several speci- 
mens the eudialyte is replaced by pseudomorphs consisting of 
aggregates of catapleiite-crystals with some analcime?. 
! Compare Meddelelser om Grønland XIV, PI. VI, Fig. 1 (1894). 
? Ibidem, PI. VI, Fig. 5 and 6. 
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