RAW QUARTZ, ITS DEFECTS AND INSPECTION 357 



which are near the concentrated focal point of the projection illumination are 

 visible in each view. The length direction of the needles must be nearly par- 

 allel to the direction of illumination to be seen well (thus wide angle of illumi- 

 nation is an aid in finding the needles). Needles elsewhere in the stone may 

 be observed by moving the stone about. The flares at the ends of the stone 

 are due to exterior surface conditions. The needles of Fig. 13 are of the 

 comet type (radiating from a point), while those of Fig. 14 lie in i>arallel 

 groups. In each case a few of the needles are slightly feathered, and all 

 are soft needles. 



Figure 4.15 shows a stone (14, in Fig. 4.5) in which the defects are con- 

 centrated in the base, a common occurrence. Were this stone to be proc- 



Fig. 4.12 — This stone, viewed in the projection light, shows phantoms A-A to B-B, 

 blue-veil C-C, bubble-veil E, and two fractures near D. 



essed by Z-sectioning, a saw cut near the line C-C would divide the stone 

 into a large, nearly perfect portion, and a small unusable portion which 

 need not be further processed. Otherwise sawn, bad portions will have to 

 be processed, or good portions of a largely bad section would be too small 

 to obtain plates from. This points out the importance of coordinating 

 processing with inspection, even though the stones have been already in- 

 spected and judged to be worth processing. 



Bubbles and cracks fill the end of the stone at B, scattered bubbles appear 

 in a veil at A , and a few isolated bubbles are at D. Note the clarity of the 

 stone relative to the fluid, as shown by the beam of light entering the stone 

 from the left, not visible internally. 



