328 QUARTZ ROCK. 



SECOND SUBDIVISION. Of quartz and mica. 



A Compact quartz with interspersed scales of 

 mica. 



a* The quartz opake, . V J 



b. The quartz hyaline. 



This latter sometimes forms the substance 

 well known by the name of avanturine, and al- 

 ready noticed under micaceous schist; the co- 

 lours varying according to those of the mica or 

 the quartz. 



B. Laminar; the lamination of the quartz being 

 chiefly determined by the position of the mica. 



a. The mica in distinct scales, dispersed, but 

 parallel. 



.1?,. The mica accumulated in distinct laminae. 



This variety passes into micaceous schist, and 

 Is eiiiimerated under that head. It forms the 

 bond of union between these two rocks. The 

 ColoJtirs^of these varielres;diflfer,-accoi*ding4o those 

 of tte mica ivhkb'thisy contains: c ;&$*& - 



