SPECIFYING QUARTZ CRYSTAL ORIENTATION 



233 



along a z axis in one direction only, the x axis does not appear to be one of 

 two-fold symmetry. Such a crystal is illustrated in Fig. 2.11. Here the 

 prism faces under a major rhombohedron are tapered and bright, the 

 prism faces under a minor are relatively parallel sided and very dull. The 

 bright prism faces are much more nearly parallel to the optic axis than the 

 dull ones. Again, given a portion of the prism we can deduce the orien- 

 tation. 



Fig. 2.11 — Another t\'pe of quartz growth 



2.3 Flat Lay Cutting 



Flat lay cutting takes advantage of the fact that, although tapering 

 quartz prisms have their faces non-parallel to the s axis the prism faces are 

 parallel to the x axis. A crystal is cemented prism face down, to a mount- 

 ing plate. The mounting plate is tilted and tur-ned on a base plate to render 

 the optic axis parallel to the long edge of the base plate. This is done in 

 a conoscope. Now the edges of the base plate are the x, y, z axes of the 

 crystal. 



The crystal can now be cut directly into wafers for dicing into AT's, 

 BT's etc. by mounting on an angle bracket as shown in Fig. 2.13 or cut into 

 X sections from which AT or BT bars shall be made by merely sawing down 

 the length. Again s sections can be cut by cross cutting. Good z sections 

 can be made in this way in the total absence of faces. These sections can 



