CHAPTER IV 



Raw Quartz, Its Imperfections and Inspection 



By G. W. WILLARD 



4.1 Introduction 



QUARTZ is one of the commonest of crystalline minerals and occurs 

 in many variations of size, color, purity, and structural perfection. 

 It is used for such varied purposes as jewelr\% fusing into heat and chemical 

 resistant dishes, and for optical and piezoelectric units. However, the 

 following discussion will be concerned mainly with such raw quartz as is 

 commercially used in the manufacture of piezoelectric circuit elements. It 

 might be added that the terminology used may be more in keeping with the 

 language of the piezoelectric manufacturers than of the geologist. Further, 

 description of many unusual types of defects, and variations of common 

 types has been omitted. An attempt is here made to describe such defects 

 as are of most interest in the piezoelectric art and in such a manner as to be 

 most widely useful. Following is a description of raw quartz and its defects, 

 the means of observing these defects, their appearance as recorded photo- 

 graphically, and a discussion of their effects on finished plates. 



The words defects and imperfections as used in this article mean a de- 

 viation from a perfect specim.en of raw quartz; they do not necessarily 

 mean that the material is not entirely satisfactory for the purposes intended. 



4.2 Source, Size, Shape 



Quartz crystals of usable quality and size come mainly from the interior 

 of Brazil. From other sources the supply is negligible, or the size too small, 

 or the imperfections too predominant. Even from Brazil only one in a 

 hundred of the mined stones is usable. The size of stones most commonly 

 used run from one-half to five pounds (about one-half cup to one quart size). 

 The shape of the stones varies from well faced material, with all of the 

 original natural faces intact, to stones in which the faces are broken or 

 eroded away. When the faces are entirely broken away by mining opera- 

 tions the stones resemble chunks of broken glass. When the faces are eroded 

 away by having been washed along river beds the stones are called RIVER 

 QUARTZ, and the appearance is that common to river stones. River quartz 

 usually exhibits a network of shallow surface cracks resulting from the 

 continual bumping along a river bed, and hence is more subject to thermal 

 and mechanical shock than uncracked stones. 



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