Ichikawa — Etched Figures of Japanese Quartz. 473 



The luster of quartz crystal is vitreous, but primary quartz 

 has a stronger luster than secondary quartz. Natural etching 

 gives a stronger luster than artificial etching ; in the latter case 

 the strong acid yields a stronger luster than the weak acid. 

 The diaphaneity of quartz crystal is from transparent to opaque, 

 but secondary quartz is more transparent than primary quartz, 

 and in secondary quartz, that from granite pegmatite is more 

 transparent than quartz in metal-veins. 



Smoky-quartz, amethyst, etc., lose color by ignition, but 

 milky-quartz does not change in this way ; ignited quartz has a 

 stronger luster and is less brittle than before ignition. 



The direction of the vertical axis of rock crystal is softer than 

 that of the lateral axes ; therefore in making hollow spheres, 

 vases, etc., the hole must be dug in the direction of the vertical 

 axis. In the direction of the vertical axis rock crystal has 

 no double reflection ; hence quartz lenses must be cut perpen- 

 dicularly to this axis. A basal section of a crystal is dissolved 

 by a strong hydrofluoric acid and its plane does not show 

 etching figures in the direction of the vertical axis, like an 

 isotropic body. 



In the above studies it has been shown that the principles 

 governing the methods of the crystal sculptors in Japan corre- 

 spond to those developed by my etching. There are numerous 

 other cases where etching and the principles revealed by it must 

 be applied to the work in quartz. 



Kitashinjo-mura, Imatate-gun, Fukui-ken, Japan, 1913. 



Art. XXIX. — Datolite from Worth Plainfield, Somerset 

 County, New Jersey ; by A. C. Hawkins. 



The datolite crystals here described were collected by the 

 writer in 1905 at the old quarry then being operated in the 

 First Watchung Mountain basalt, at North Plainfleld, New 

 Jersey, by the Wilson Crushed Stone Company, now operat- 

 ing on adjoining property. 



The crystals were found upon two specimens, viz : — Speci- 

 men No. 1 exhibits a large number of intergrown individuals 

 having an average size of 4x2"6x2'2 min , the largest measured 

 being 7x4x5 mm , and the smallest 3Xl'oXl'5 mm . Their color 

 is white to very light green, and their luster is vitreous. 

 They are implanted upon a somewhat porous and granular 



