MAGMATIC DIFFERENTIATION OF IGNEOUS ROCKS 643 
norite from Erteli, Norway, which, according to the analysis of the 
entire specimen, only contains o.07 per cent S=o.18 per cent 
pyrrhotite, here and there accumulated in small lumps. 
For the photomicrograph was chosen a locally pyrrhotite-rich 
part of the thin section, otherwise free from pyrrhotite. That 
pyrrhotite also crystallized last in common norites and gabbros is 
due to the circumstance that the intervals of the crystallization 
Fic. 46 ! FIG. 47 
Fic. 46.—Photomicrograph between crossed nicols (15:1). Pyrrhotite in norite 
from Erteli, from the same thin section as Figures 15 and 16. The rock contains 
©.07 per cent S. Figure 46 is from a portion rich in pyrrhotite. 
Fic. 47.—Quartz-norite from Romsaas, Norway (20:1). Illustrating a portion 
rich in pyrrhotite, from the same thin section as Figure 10. The hypersthene, biotite, 
and labradorite show idiomorphic contours against the pyrrhotite, and small veins 
of pyrrhotite cross the silicates. 
for the silicates lay somewhat above, but for the pyrrhotite a little 
below, 1200°. 
As well in pyrrhotite-hypersthenites and -norites, etc. with 
quite much pyrrhotite, as in the common norites, etc. with only 
about o.2-0.5 or 1 per cent pyrrhotite, we frequently find veins of 
pyrrhotite branching off from relatively larger accumulations of this 
mineral, and intersecting the neighboring minerals. 
We refer to igure 47, wnere we see quite thin veins of pyrrhotite 
intersecting the hypersthene and the labradorite, which otherwise 
