466 Ichikawa — Etched Figures of Japanese Quartz. 



6, B), 3 has a new face like — %R (figs. 6, A, and 10, A, etc.), 

 4 has a larger angle than the normal angle (fig. 10, B). The 

 position of grooves on the prismatic edges of natural etching is 

 opposite to that of quartz crystal etched with hydrofluoric acid. 



4. Vicinal Faces of Japanese Quartz (with Plate VI). 



Artificial and natural etching of quartz crystal have already 

 been described by mineralogists, but not the characteristics of 

 the vicinal faces of the crystal, which are closely connected 

 with these etching figures. ln_1909, I first observed a smoky 

 quartz from Tanokamiyama, Omi Province, with a different 

 vicinal face on its positive and negative rhombohedral faces ; 

 since then I have collected a number of interesting quartz 

 crystals with vicinal faces accompanied by natural etching on 

 a rhombohedral face.* The results of the study of these 

 vicinal faces are illustrated in the following plate : 



Plate VI. 



The size of the vicinal forms on the rhombohedral faces is 

 larger than the natural pits on the same face, and they can 

 usually be observed by the naked eye. 



Fig. 1 shows vicinal faces on a Dauphine twin of left-handed 

 rock crystal from Kinbuzan. Fig. 2 is a horizontal projection 

 on a pyramid of a left-handed cairngorm with vicinal faces 

 from Naigi, Mino Province. Fig. 3 is a left-handed smoky quartz 

 from the same locality as fig. 2. Fig. 4 is a left-handed rock 

 crystal from Takemori. Figs. 5 and 6 are left-handed rock 

 crystals from Kinbuzan ; fig. 6 is a Dauphine twin with 

 numerous irregularly developed vicinal faces. 



Figs. 7 and 8 are right-handed smoky quartz from Tano- 

 kamiyama, Omi Province ; fig. 7 is a Dauphine twin. Fig. 9 is a 

 Dauphine twin of right-handed smoky quartz from Naigi. 

 Fig. 10 is a right-handed rock crystal from Takemori. Fig. 11 

 is a Dauphine twin of right-handed smoky quartz from Tamo- 

 kamiyama. Fig. 12 is a Dauphine twin of right-handed rock 

 crystal from Kinbuzan ; the pyramid has innumerable irregu- 

 larly developed vicinal faces. 



Fig. 13 is a Dauphine twin of left-handed smoky quartz from 

 Tanokamiyama. Fig. 14 is a Dauphine twin of left-handed 

 smoky quartz from Kamikane, already shown in Plate V, fig. 

 10, B ; the pyramid has many vicinal faces and natural depres- 

 sions on its surface. Fig. 15 is a right-handed rock crystal 

 from Kinbuzan, with a few vicinal faces and many natural 

 pits ; A and B show the pyramid on both ends of the prism. 



* Jour. Geogr. Tokyo, vol. xvi, 495, 1909 ; xvii, 239, 1910, and the correc- 

 tion in vol. xvii, 526, 1910 ; vol. xviii, 82, 1911. 



