241 
In both cases the extinction angle in seclion parallel to the 
symmetry plane (010) is about 45°, and likewise the augite has 
often a narrow green border zone in which the angle с:а is 
somewhat smaller, indicating a slight admixture of the egirine- 
molecule. In some specimens (both olivine-bearing and: the 
opposite) the augite is accompanied by or replaced by an 
ægirine-augite with an extinction angle с: a amounting to 
about 25°, and sometimes with a border zone of almost pure 
ægirine. 
The hornblende in this rock is of a brown colour. The 
extinction angle c:c is about 15—20° and the pleochroism- 
scheme is: 
a entirely light brown 
b dark brown 
c dark greenish-brown. 
It is allotriomorphic and occurs in greatly varying quantities, 
in some specimens it is almost as plentiful as augite, in others 
it is very scarce. It is often found in parallel intergrowth 
with augite, thus, an augite crystal may enclose many small 
irregular areas of hornblende, and at the same time be sur- 
rounded by this mineral. Sometimes a narrow border of pale 
green augite surrounds the hornblende. Biotite flakes of a 
deep brown colour are usually present to a very small extent 
only; as a rule they are associated with iron ore. 
Felspar, the chief constituent of the rock, is a soda-ortho- 
clase. The extinction angle is about 11—13° in sections раг- 
allel to (O10). Sometimes it is quite homogeneous, and in 
such a case vaguely defined specks may be found in the сгу- 
stals which, among the crossed nicols, show an extremely fine 
cross-hatching indicating the presence of soda-microcline. More 
frequently the felspar among crossed nicols has a more or less 
irregular patchy or moire appearance due to variations in the 
chemical composition. As a rule the central portions of the 
XXXVIII. 16 
