66 ; Pentti Eskola. 
There are always sharp boundaries between the orthite ; 
and the surrounding epidote, indicating the former to be 
decidedly of an earlier crystallization. In the epidote the 
angle c:o is but 6” in the acute angle £, i. e. inclined to the 
same direction as in the orthite. The negative axial angle 
may be estimated at about 70”. The colours are faintly 
discernable: « = pale greyish brown, £ = nearly colourless, 
y = greenish yellow. The scheme of the absorption is 
a>p<y, or opposite to that in the orthite. 'y—o is about 
0038-05 
From the birefringence of this epidote it may be con- 
cluded to contain approximately 35 per cent of the ferric 
compound (HCa,FezSiz0,3) or a little more than 15 per 
cent weight of Fe,0sz. i 
The epidote is almost always intergrown with quartz. 
This is a very striking phenomenon, as quartz, in most of 
the specimens, was not at all to be found elsewhere in the 
thin sections. The character of the intergrowth is that of 
the myrmekite, the quartz forming vermicular channels in 
the epidote. Sederholm has already mentioned this inter- 
growth among his »synantetic» minerals "). | 
The boundaries between this myrmekite and the feldspars 
show that the former has originated contemporaneously -' 
with the last part of the feldspars. 
The question might be asked: why has the epidote 
crystallized out in such rock that contains a very sodic 
plagioclase? The calcium aluminium silicate could very well 
have formed more anorthite. The cause why a hydrous 
silicate originated was probably that the temperature was 
low enough to allow it. Examples of similar nature are the 
occurrence of vesuvianite as a magmatic mineral in the 
canadite from Almunge, Sweden ?) and the occurrence of 
2) J. J. Sederholm, »On Synantetic Minerals and some Related Pheno- 
mena (Reactions Rims, Coronas, Myrmekite etc.)» Bull. Comm. Geol. Finl, 
No 48 (1916). 
2) P. Quensel, >The Alkaline Rocks of Almunge>, Bull. of the Geol. 
Instit. of Upsala. Vol. XII (1914). 
(LIL 
3 
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