ETCH TECHNIQUE 



17 



seen that the positive and negative X-surfaces produce different etch-pits, 

 and are thus usable in determining electrical sense. Further, the pits on all 

 surfaces have directional properties which allow them to be used for deter- 

 mining the approximate directions of the axis which lie in the etched surface. 

 However, to be able to determine orientations from etched surfaces of other 



/ LEFT HAND QUARTZ^x 

 / ^ ■ ^ \ 



/ RIGHT HAND QUARTZES 



ON 

 COMPRESSION 



BT^ 



0- 



in conoscope : contracting rings 

 (eyepiece rot clockwise) 



in polariscope-. analyzer 

 rotated counter-clockwise 



in conoscope- expanding rings 

 (eyepiece rot. clockwise) 



in polariscope : analyzer 

 rotated clockwise 



Fig. 5.4 — The conventions of handedness, axes, natural faces, and angular sense-of-cut 

 of common oscillator plates, together with the electrical and optical rules for determining 

 these characteristics in unfaced stones. 



orientations than those shown above, requires a knowledge of the appear- 

 ance of the etch-pits developed on such surfaces. 



A rather complete catalog of etch-pits on all possible surfaces of quartz 

 was prepared by W. L. Bond,^ using an etched sphere of quartz (Figs. 5.5, 

 5.6 are from Bond). Thirty-sLx different types of etch-pits were obtained 

 and their angular range of coverage was found (the X-, Y-, and Z- surface 



^ "Etch Figures of Quartz," Z. Kristallogr. (a) 99, 1938, pp. 488-498. 



