Ichikawa — Etched Figures of Japanese Quartz. 471 



positive edges with positive ion (Si), which belong to the ter- 

 ritory of the positive lateral axes are attacked by the acid with 

 negative ion (F), the phenomenon will be easily understood. 



When quartz crystal is naturally etched, a groove will be 

 found on each negative edge of its prism (see Plate V, figs. 1 

 and 2, etc.) ; this is understood if we assume that the prismatic 

 negative edges with negative ion (O), which belongs to the 

 area of the negative lateral axes, are attacked by a natural sol- 

 vent (salt of K, Na, etc.) with positive ion. 



Rhombohedral pole edges of the combination of -\-R and 

 + R or — R and — R in a quartz crystal develop a groove in 

 hydrofluoric acid, and the edges have also the same result 

 through natural etching ; this can be understood if we assume 

 that the crystal-molecules of the edge to take its place in the 

 direction of the intermediate axes keep the condition of neu- 

 trality with each other (see Plate I, n'g. 1 ; Plate V, fig. 1, 

 etc.). 



The basal section of quartz crystal is attacked equally by 

 hydrofluoric acid ; this is clear if we assume that the crystal- 

 molecules on the plane keep the condition of neutrality with 

 each other (see Plate YII, figs. 5-8). 



A quartz crystal is more easily cleaved in the direction of 

 the intermediate axes than in other directions ; which suggests 

 that the crystal-molecules of quartz are regularly arranged in 

 the direction of the intermediate axes as in the above models. 



When two rock crystals are struck together with each other 

 by their prismatic edges, the crystals will emit a phosphor- 

 escence (triboluminescence) on each individual ; if we may 

 assume that this is an electric light by which the negative and 

 positive electricities of the crystal-molecules, developing as the 

 reaction of striking together, neutralize each other with the 

 electricities of the adjoining crystal-molecules in a moment, the 

 phenomenon will easily be understood. Besides amethyst, 

 milky quartz emits phosphorescence, but (cairngorm, smoky 

 quartz, etc.), do not emit it, except after their color is lost by 

 ignition.* 



The phenomena of pyro-electricity and piezo-electricity, 

 etc., can also be explained by the above models, but whether 

 the quartz crystal has the simultaneous development of posi- 

 tive and negative charges of electricity on different edges of 

 the crystal, as well by etching as by temperature or pressure, 

 can not be determined, unless after an exact measurement. f 



* See my note " On the relation between the colors and phosphorescence 

 of quartz," (Toyogakugezatsushi No. 334, p. 355, 1909, and Jour. Geogr., 

 Tokyo, vol. xvi, p. 234, 1909). 



fSee my note "On the development of electricity on quartz crystal." 

 Toyogakugezatsushi, No. 346, p. 338, 1910. 



Am. Jour. Sci.— Fourth Series, Vol. XXXIX, No. 232. -April, 1915. 

 31 



