MAGMATIC DIFFERENTIATION OF IGNEOUS ROCKS 631 
In the norites, relatively rich in hypersthene but quite poor in 
magnetite (and ilmenite), the crystallization of iron ore did not 
commence until some part of the hypersthene had solidified. Asan 
example we choose a norite from Skougen in Bamle, which, accord- 
ing to the chemical analysis (see the section on norite in Part II), 
contains 1.09 per cent TiO,, 1.44 Fe,O;, and 9.42 FeO. The 
mineralogical composition is about 47 per cent hypersthene (with a 
little secondary hornblende), 3 per cent biotite, 48 per cent labra- 
dorite, and about 1-2 per cent iron ore, and in addition a little 
Fic. 29.—Photomicrograph (21:1) Fic. 30.—Drawing (21:1) 
Hyperitic-structured olivine-gabbro from Elverum, Norway. Consisting of ca. 
65 per cent labradorite, 10 per cent olivine, 10-15 per cent diallage, 3-5 per cent 
biotite, and ca. 2 per cent magnetite (with a little ilmenite). 
apatite and pyrite. An essential part of TiO, and Fe.O, enters 
into hypersthene and biotite. In most parts of the thin section 
(see Fig. 13) iron ore is lacking as it only appears in a few places.’ 
Here the hypersthene shows an idiomorphic contour against the 
magnetite, and this applies especially to the relatively small indi- 
viduals of hypersthene, which partly have an entirely straight 
crystallographic boundary against the magnetite (with ilmenite). 
The latter, on the contrary, shows no signs of idiomorphic out- 
lines. Some part of the hypersthene must thus have solidified 
before the formation of the magnetite. Since especially the small 
1 For this reason we are not able to determine the quantity of the iron ore with 
precision by a planimeter calculation of the thin section. 
