Ichikaiva — Notes on Japanese Minerals. 129 



corresponds to the rhombohedral type ; the resulting 

 form in the etching again is repeated as follows : 



a. At the beginning of etching, the faces — %J2, mR, 

 & R, cc Pn, etc. form new faces of a rhombohedron (see I, 

 figure 1, A; figure 4, B; figure 5 (abc) ; also II, figure 

 1, A, B, etc.) in the direction of striatums on their crys- 

 tal faces, and natural pits on the new rhombohedron much 

 resemble pits on the cleavage face (compare figures 2, 3, 

 4, etc. in II). 



b. In the progress of etching, the faces R, mRn, etc. 

 yield new forms resembling an acute trigonal pyramid 

 (see I, figure 1, M, N, and figure 2, etc.) in the direction 

 of the vertical axis and the position of the lateral axis of 

 the new form also corresponds with the position of the 

 axis of rhombohedron (+ E) in the crystal. 



IX. Natural pits of Zincblende Crystals (III). 



In 1908 I visited the Kuratani mine in Kaga Province 

 and collected zincblende crystals with natural pits. 

 The results of the study of these natural pits are shown 

 in the accompanying figures (III). The crystals occur 

 in a clay vein, color black ; luster brilliant ; habit tetra- 

 heclral with traces of the dodecahedron mOm, etc. They 

 measured 3 to 8 mm. in diameter, penetration twins are 

 often observed and simple crystals are very rare; the 

 natural pits were more often found in the former than 

 the latter. Polysynthetic twins can be barely observed 

 by the naked eye, and the natural pits, striations, etc. can 

 only be investigated under a magnification of 75 to 140 

 diameters. Figure 1 (III) shows hexagonal pits and trig- 

 onal elevation on the tetrahedral faces (X 8). Figure 2 

 shows two hexagonal pits on the tetrahedral face ; the 

 angles are: aob = 75°; cob = 45°. Figure 3 shows 

 two groups of hexagonal pits. Figure 4 shows two equi- 

 lateral trigonal pits. Figure 5 shows an equilateral trig- 

 onal elevation on the tetrahedral face; the direction of 

 the elevation is opposite to that of the pit. 



Fig. 6 shows the relation between the outlines of hex- 

 agonal pits and the edges of a tetrahedron (with o\ d, a, 

 and mOm, etc.), in a horizontal projection on the trigonal 

 axis. The wall of V-shaped pits (£') on the dodecahedral 

 face is parallel to a large wall (t) of hexagonal pits on 

 the tetrahedral face (see figure 11, A). Figure 7 is the 



Am. Jour. Sci.— Fourth Series, Vol. XLVI1T, No. 284.— August, 1919. 

 9 



