822 C. IWASAKI 
ingredient in the rock, under the microscope is somewhat clear 
and fresh, exhibiting the extinction angle of labradorite. The 
albite type is the most common among twins, and the pericline 
type, also, is frequently found in the same individuals. Zonal 
structure, with different optical orientation, is often met with. 
Sometimes the core exhibits an eight-sided section, while the 
outline of the whole crystal is nearly rectangular. The crystal 
is often partly idiomorphic and partly allotriomorphic. It 
usually contains glass enclosures, which are seldom zonally 
arranged. Sometimes immovable gas bubbles are seen. The 
presence of liquid enclosures is very uncertain. The feldspar is 
generally fresh and clear. Decomposition begins at the cracks, 
where epidote grains are produced. In some cases they entirely 
replace the feldspar. 
Next to the feldspar, the most abundant mineral is horn- 
blende, either fibrous or compact, which fills up the interspaces 
between feldspar crystals. The characteristic cleavage along 
(110) is very distinct. The prevailing color is green, with the 
following pleochroism: g = greenish brown, b = brownish green, 
¢— green. The extinction angle 1s) about) 12;) but, the decome 
posing individuals exhibit an undulatory extinction. Many of 
the hornblende crystals are derived from augite. The sections of 
the latter are brownish in color, with a greenish tinge, compact 
in texture, with their characteristic cleavage and an extinction 
angle of about 38°. Sometimes such a compact augite is con- 
verted into one with granular texture, each of the grains retain- 
ing the optical property of augite. The granular augite is con- 
verted into fibrous hornblende. These fibers are generally 
united in bundles, parallel to each other. The vertical and ortho- 
axes of the primary augite and of the secondary hornblende 
are nearly always in parallel position, sometimes forming a 
pseudomorph of hornblende after augite, which is distinctly 
seen in cross section. The green fibrous hornblende is further 
decomposed into epidote grains or chlorite. Occasionally all 
these stages of alteration may be seen in one section, surround- 
ing each other in regular order. 
