We pushed the ship against a small banded berg, from which Wordie secured several large lumps of biotite granite.
The minerals at contact are quartz, biotite, magnetite and hornblende.
Sphene, biotite and iron oxides are the other common constituents, but these rocks show much variety of composition and structure.
There is some sericite present, also magnetite, resulting from the decomposition of the biotite.
biotite and all ferromagnesian minerals rarely appear in them, and never are in considerable amount.
biotite occurs in some of these rocks, and melanite also is present.
In other cases the spheroids are simply dark rounded lumps of biotite, in fine scales.
In other minerals the measurements are not quite the same as in biotite.
Green augite and hypersthene form a considerable part of these rocks, they may contain also biotite, hornblende and quartz.
The biotite is brown; the hornblende brown or greenish brown; the augite usually green.