Ichikaioa — Etched Figures of Japanese Quartz. 465 



to the vertical axis of the crystal, and its negative edges are 

 rounded by the etching. 



Fig. 7 gives horizontal projections on the rhombohedron of 

 rock crystals with natural etching from Yusen ji ; the double 

 lines show rounded edges by etching, and a triangle on the cen- 

 ter shows a pit that is produced in the direction of the vertical 

 axis by etching, (ah) in fig. B shows a groove that is formed 

 on the rhombohedron by etching. The direction of rotation is 

 not shown. 



Fig. 8 is the natural etching of rock crystals from Kamioka- 

 mine, Hida Prov.; its rhombohedron has ridges suggesting the 

 trapezohedral form found on the poles of the etched quartz 

 sphere (see PI. Ill, tigs. 1 and 2, B, C, and PI. IV, fig. 3, A, 

 etc.), A is a front view, and B a horizontal projection on a 

 rhombohedron. Fig. 9 is the natural etching on the prism of 

 a rock crystal from Kinbuzan ; the depressions in A much 

 resemble those of fig. 5, B. 



Fig. 10 is the natural etching of a smoky quartz from 

 Kamikane, Kai Prov. A gives a front view, and B a hori- 

 zontal projection on the vertical axis of A ; the double line on 

 each edge shows a new fac,e formed by etching that resembles 

 that of fig. 6, A. Both sides of the pole edges of (ab) and 

 (cd) have striations formed by etching, and the angle is larger 

 than the normal angle of quartz ; (xy) shows a fissure with 

 many depressions. C shows varieties of the natural pits on the 

 rhombohedron. D shows the difference between the outlines 

 of a natural depression of Molengraaff (b) and 1(a) on a rhombo- 

 hedron of quartz. 



Fig. 11 shows varieties of the natural pits on the rhombo- 

 hedron and prism of a foreign quartz which Molengraaff first 

 observed (compare fig. 5, A). See also the results of Dr. K. ' 

 Jimbo on the natural etching of a rhombohedron of Japanese 

 quartz.* 



The natural pits on the rhombohedron of fig. 5, A, do not 

 reveal the distinction between the positive and negative forms as 

 do those in fig. 11 taken from Molengraaff 's work. Also while 

 the natural depressions on the prism of fig. 5, A, and fig. 9, 

 B, etc., reveal the direction of rotation, the symmetry of the 

 natural pits on the prisms of fig. 5, B, and on the rhombo- 

 hedron of £.g. 5, A, do not correspond to the trapezohedral 

 symmetry ; therefore the method that determines the positive 

 and negative rhombohedrons by Molengraaff's model figure 

 (fig. 11) cannot be applied to natural etching of the above 

 Japanese quartz. 



The varieties of edges modified by etching are classified as 

 follows : 1 has grooves (figs. 1, 2, etc.), 2 is rounded (fig. 



* Jour. Geogr., Tokyo, vol. iv, 172, 187, 1897. 



