440 DR. BUNDJIRO KOTO ON SOME JAPANESE ROCKS. 
magma and not by decomposition in the ordinary sense of the 
term used by Oebbeke) the iron in the hornblende becomes separated 
as magnetite or as some silicate of iron, and the residual substance 
will contain a higher percentage of lime in proportion to the decrease 
of iron, so that the resulting substance will have approximately 
the composition of augite. Oebbeke* says that when hornblende 
is for a long time strongly ignited, it becomes dark brownish-red, a 
change due perhaps to the oxidation of iron, while augite remains 
totally unaffected. © 
Mitscherlich, Berthier, and G. Rose f have shown that fused amphi- 
bole, in solidifying, crystallizes in the pyroxene-form, while pyroxene 
reassumes its original configuration. Hoépfner £ and Oebbeke $ 
share the same view. Therefore the transformation of hornblende 
into augite appears by no means surprising. The experiment made 
by Dolter and Hussak || corroborates this fact. 
In addition to the augite-grains matnetite also occurs in the 
opacite margins, being sometimes sufficiently abundant to form 
pseudomorphs after hornblende. In other cases hornblende under- 
goes another mode of decomposition, and assumes a fibrous structure, 
in which condition it bears a great resemblance to enstatite. ‘The 
fibrous hornblende is pleochroic. C=dark green. B=brownish 
green. A=light green. C>B>A. ¢:C=17. 
Enstatite occurs only in a few andesites. It is found in 
rectangular sections, the colour being green or brown. It exhibits 
fine rectilinear striations and is distinctly pleochroic. C=sea-green. 
A or B= reddish brown. This rhombic pyroxene of course 
extinguishes the light parallel to the crystallographic axes. Be- 
sides the vertical striations, the enstatite is irregularly crossed by 
transverse veins. Very fine silky asbestiform fibres (chrysotile?) 
pass at right angles from these veins, along which decomposition 
has commenced. 
This enstatite contains colourless needles and grey rounded 
crystals in great abundance. 
Apatite—Though not present in large quantity, apatite is, 
however, widely distributed, and may perhaps be ranked as an 
essential ingredient of andesitic rocks. In these it occurs in the 
form of crystals with rounded edges, and never shows a finished 
crystallographic form. Apatite is usually grey, brown, or almost 
black, these various tints being due to microscopic interpositions 
of cylindrical pores and opaque rods, which are mostly grouped in 
the centre of the crystals. 
In one specimen the apatite contains an apatite microlith, showing 
the combination o P, P, OP; and in another are liquid-enclosures 
with vibrating bubbles. 
The imperfect form of the apatite individuals may be due to a 
* Neues. Jahrb. i. Beilage Band, p. 475. ‘‘Beitrage zur Petrographie der 
Philippinen und der Palau Inseln.” 
t+ Naumann-Zirkel, ‘ Mineralogie,’ 1lte Auflage, p. 597. 
t Neues Jahrb. i. 1881, p. 172. § Loe. cit. 
| N. Jahrb. f. Mineralogie, &c., 1884, i. Band, p. 25. 
