Ichikawa — Etched Figures of Japanese Quartz. 457 



outline of a trigonal trapezohedron and has pits of 7-like 

 shape on its faces. Fig. 2 is a right-handed crystal from the 

 same locality, A, B, C, and D corresponding to A, B, C, and D 

 of fig. 1. 



Fig. 3 shows the etching of a left-handed quartz, forming 

 phenocrysts in a quartz-pro phyry from Otomezaka, Kai Prov- 

 ince. Fig. 4 is on a Dauphine twin of right-handed quartz 

 from the same locality. Fig. 5, A, is a Brazilian twin of rock 

 crystal from Takemori ; B, a horizontal projection on the 

 vertical axis of A. 



Fig. 6 is a horizontal projection on the vertical axis of the 

 parallel-growth of left-handed and right-handed rock crystals 

 from Yusenji, Kaga Province. Fig. 7 shows the same for a rock 

 crystal from Kinbuzan, Kai Province ; the crystal appears like a 

 simple crystal, but has a trigonal trapezohedron on its left and 

 right sides. 



Fig. 8 is an etched Dauphine twin of right-handed rock 

 crystal from Takemori, in horizontal projection on its vertical 

 axis. Fig. 9 is a front view of a model-crystal of left-handed 

 Dauphine twin ; fig. 10 one of a right-handed Dauphine twin, 

 and fig. 11 of a Brazilian twin. 



The symmetry of the pits on the above crystal faces, and 

 the position of the grooves on the edges, correspond to the 

 trapezohedral symmetry. The pits on the rhombohedron, 

 trigonal pyramid and trapezohedron, etc., can be formed by 

 dilute acid, but those on the prism can be obtained distinctly 

 only by pure acid. The trigonal pits and 7-like shaped 

 depressions in fig. 1, D, etc., are formed by a more dilute acid 

 than in the other two cases. The grooves on the edges of the 

 prism can not be formed so regularly as those on the rhombo- 

 hedral edges, etc. 



The extremities of the vertical axis are more quickly dis- 

 solved away than the lateral axes, and those of the positive 

 lateral axes more quickly than those of the negative lateral 

 axes ; therefore, the resulting form in the etching proves to be 

 a form resembling a trigonal trapezohedron. 



2. Artificial Etched Figures of some Spheres of Japanese 

 Rock Crystal (with Plates III and IV). 



The artificial etching of a quartz sphere with hydrofluoric 

 acid has already been described by Dr. Otto Meyer and 

 Samuel L. Penfield."* In that paper, however, the order in 

 which the modifications of the sphere occur, in the interval 

 between the beginning and end of the corrosion, has not been 



* Transactions of the Connecticut Academy of Arts and Sciences, vol. viii, 

 pp. 158-165, 1889. 



