118 
magnesian mineral. It occurs in allotriomorphic anhedra which 
are somewhat unevenly coloured. In sections parallel to the 
plane of symmetry (010) the absorption-tints are: — 
c (or b) rather dark dirty-brown or greenish-brown 
a light brown or sometimes reddish-brown. 
In cross-sections the absorption-tint for 6 (orc) is found to be 
dark grayish-brown. The angle of extinction с:а varies from 
60° to 70°, it is distinctly larger for green than for red light. 
This hornblende has a dark blue marginal zone with the cha- 
racters of arfvedsonite (с:а == са. 10°), and there is a gradual 
transition from the greenish-brown core to the blue marginal 
zone. The angle between the a-axes of the two hornblendes is 
50° to 60°. The directions of the cleavage are the same in 
the nucleus and in the marginal zone. indistinctly bounded 
dark blue patches may also be found in the interior of the 
greenish-brown hornblende. 
The egirine-augite occurs in varying amounts and is 
sometimes entirely wanting. It is of the ordinary intense green 
colour. In sections parallel to 5 (010) the angle of extinction 
с:а is about 30°; in the central portions, however, the colour 
is lighter and the extinction-angle с:а is greater. This mineral 
occurs in parallel intergrowths with the catophorite-like horn- 
blende. It is especially abundant within a narrow zone imme- 
diately surrounding the sandstone-fragments. 
Chemical compositon. — A typical light-gray, rather fine- 
grained specimen (without ægirine-augite) was selected for the 
chemical analysis. This was made by Mr. С. Derrersen with the 
results given in No.2 in the table p.114. It will be seen that 
the composition closely agrees with that of the Ilimausak gra- 
nite, and that the only remarkable difference is the very low 
amount of lime. 
