NOTES ON SOME IGNEOUS ROCKS OF JAPAN 663 
Quartz is present in small amount as shown by the chemical 
analysis, but it is sufficient to characterize the rock as quartz- 
bearing syenite. It occurs interstitially, or intergrown micro- 
graphically, with the alkali feldspar, and frequently as an 
infiltration in miarolitic cavities with zeolite. In the last case, 
it often shows distinct euhedral outline. 
Biotite is sparingly present, and usually occurs associated with 
hornblende. It is optically negative, and the plane of the optic 
axes lies in the plane of symmetry. The optical angle measured is 
2E=36° 23’. The pleochroism is strong: X, brownish-yellow; 
Y, brown with violet tinge; Z, dark reddish-brown; and absorp- 
tion, Z>Y>X. Magnetite and apatite are included in it. 
The diopside shows an irregular form and is colorless or pale 
violet, being slightly pleochroic. Its quantity is variable and it 
shows a tendency to replace hornblende. Olivine occurs in more 
or less automorphic outline, and is quite fresh. It is almost free 
from inclusions with the exception of a few minute crystals of 
magnetite and apatite. The ilmenite and magnetite are present in 
association with each other. The former is in irregular form and is 
characterized by the decomposed product, leucoxene. Apatite 
occurs conspicuously in elongated prismatic form. It is compara- 
tively abundant. 
_ The mineral described here as allanite is not exactly determin- 
able, owing to its rare occurrence and deep color, in some instances 
being almost opaque. It is strongly pleochroic from deep reddish- 
brown to opaque. In some respects, it resembles aenigmatite or 
rhonite. Its form is long prismatic with irregular terminations. 
Zonal structure is not recognizable, and cleavage is also indetermin- 
able. One section observed is cut nearly perpendicular to an 
optic axis, its cross-bar appearing in the middle of the field. The 
case 1s very similar to that of the allanite-like mineral in the Mt. 
Belknap syenite, described by Pirsson and Washington. The 
characters of the mineral will be determined after further examina- 
tion of more thin sections. 
Chemical character.—The analysis of the rock, collected from the 
‘eastern foot of Takuhi-yama, Ezirigasaki, Kuroki-mura, Dozen, was 
made by K. Yokoyama in the laboratory of the Survey. Itisgiven. 
