ELKCIKON AIKKOSCOPY 



Fig. 9. Synthetic sylvite (KCl). The beauti- 

 fully revealed cubic cleavage contrasts strikingly 

 with curved surfaces. X 10,300. 



Fig. 10. Quartz fracture surface. Collodion- 

 carbon replica, Pd-shadowed. Evidence of crystal- 

 lographic control of the fracture pattern is prom- 

 inent in the fine as well as the coarse fracture lines. 

 X5,700. {Courtesy of A. van Valkenburg and 

 Elisabeth Mitchell, Constitution and Microstructure 

 Section, Mineral Products Division, National 

 Bureau of Standards) 



subjects have received much attention from 

 electron microscopists. Figures 9-14, illus- 

 trating some typical surface features, can 

 only suggest the nature and extent of this 

 large and rapidly expanding area of mineral- 

 ogical study. 



Figures 9 and 10 contrast the cubic cleav- 

 age of sylvite (KCl) with the more irregular 

 but apparently crystallographically-con- 

 trolled fracture parallel to the X-cut of a 



o 



quartz crystal. Figure 11 shows 50 A growth 

 steps observed at very high magnification on 

 a crystal of the zeolite pictured in Figure 7. 

 In studies such as this the electron micro- 

 scope has played an important role in help- 

 ing to delineate the type of growth step 

 pictured here from that produced in spiral 

 growth. 



Etching techniques have long been im- 

 portant in the investigation of structure, 

 crystal growth and chemical stability (55) 

 and the electron microscope has greatly ex- 

 tended the apphcability and utility of this 



Fig. 11. Synthetic zeolite A. Platinum -carbon 

 replica showing 50 A growth steps on a cube face. 

 X59,000. (Courtesy ofD. W. Breck, Linde Company} 



194 



