662 SH KOGU: 
show slightly higher refraction and birefringence than the latter. 
The extinction angle of the shell is -+-10° on a section nearly parallel 
to (oro), while the inner part shows +7° on the same section. 
From these characters, the outer material must be referred to a 
variety of anorthoclase with especially high content of soda. In- 
clusions are plagioclase, sharply defined apatite, a few crystals of 
zircon, magnetite, and quartz. The last mineral appears micro- 
graphically intergrown in the peripheral part of the feldspar. No 
microcline structure is observed. The oligoclases usually occur in 
prismatic form and are, in many instances, included in the alkali 
feldspar. They show distinct polysynthetic lamellae and are clearer, 
owing to fewer inclusions, than those in the alkali feldspar. They 
vary in composition within a limited range, judging from their 
indices of refraction. Generally the refractions are slightly higher 
than those of quartz and Canada balsam and the maximum sym- 
metrical extinction angle of a calcic variety exceeds 17°. 
The hornblende is mostly greenish-brown, associated with a 
bluish-green variety. Its form is irregular in general; sometimes 
more or less idiomorphic in elongated or short prismatic form. 
Cross-sections exhibit the characteristic cleavage and rhombic 
outline, or sometimes six-sided section elongated along the axis b, 
having the first pinacoid strongly developed and with the unit 
prism subordinate. The bluish-green variety occurs as fringes or 
borders, and as inclusions in the brown, and as an individual of 
quite irregular shape in very rare instances. In the first instance 
the green variety does not entirely inclose the brown, and in many 
instances it occurs on the terminal faces of the brown crystal. 
These two varieties exhibit almost no differences in optical orienta- 
tion. They are strongly pleochroic: X, light yellow; Y, dark 
brownish-yellow; Z, greenish-brown to olive-green; absorption . 
Y>Z>X, on the greenish-brown variety, and_X, light yellow; Y, 
yellowish-green; Z, bluish-green;. absorption Z>Y>X, on the 
bluish-green variety. They extinguish in nearly the same position — 
and the angle between Z and c on (o10) is from 26° to 28° in the 
obtuse angle B. From these properties, the hornblende seems to be 
barkevikite near katophorite or hastingsite, but it is not like it in 
the larger optical angle (?) and the higher birefringence. 
