1 84 The Ainerica7i Geologist. September, 1900 
The augite often contains inclusions apparently identical 
with what Schrauf has named microphyllites and microplakites 
in labradorite. They will receive further study later. Liquid 
inclusions have not been observed in augite, though they have 
been found rarely in the olivine, and in the apatite. 
The alteration of the labradorite is both endogenetic* and 
exogenetic*. It results most commonly in the production 
of penninite, calcite and a sericitic mineral, probably musco- 
vite. 
The augite alters to biotite both brown and green, as well 
as to hornblende and chlorite with frequent attendant separa- 
tion of magnetite. Occasionally the iron seems to separate 
out as pyrite. Hematite may be formed any where in the 
rock. 
Biotite is oftenest formed by mesogenesis between the 
magnetite and the labradorite. 
The che7nical composition of the normal diabase is given 
below. The titanium is undoubtedly mostly contained by the 
augite, which is slightly pink in thin section, and by the mag- 
netite. The water is low corresponding to the slight decom- 
position which the rock has suflfered. 
I 
SiOg 47-9° 
TiO, 57 
FcgOg 19.92 
FeO 9.78 
MnO trace 
MgO 4.55 
CaO 8.56 
NaoO 2.75 
K.6 56 
HgO 76 
100.39 
Specific gravity 2.93 
I. Diabase from east side, of Birch lake (954). (The specimen is 
poor in olivine.) No appreciable BaO nor SrO; P2O5 and CO- not de- 
termined. 
*The definition of these terms will be given in chapter IV. 
