ELECTRON MICKOSCOrY 



Fig. 6. Synthetic chrysotile asl:»estos. The 

 tubuhir crystals have internal diameters of 

 50-lOOA but vary widely in outer diameter. The 

 "cone-in-cone" habit is common only in synthetic 

 material. X02,000. 



ural the electron microscope has been inval- 

 uable in studying their applicability to and 

 usefulness in many industrial applications. 

 The replica showing the kaolinite flakes in 

 Figure 5, for example, was made of a sheet of 

 paper such as that you are now reading, the 

 role of the clay particles being to provide the 

 high gloss necessary for good reproduction of 

 illustrations. To obtain maximum reflectiv- 

 ity the perfection and orientation of individ- 

 ual crystals is of utmost importance, and 

 platinum-carbon replicas such as that shown 

 have provided vital information to the paper 

 coating trade (24). Similarly, fundamental 

 work has been done on subjects such as Ti02 , 

 iron oxide and other mineral pigments in 

 paint and enamel (25, 26, 27, 28), crystals in 

 glass (29, 30), diamond powders (31), and 



calcium-silicate hydrates in cement (32, 33, 

 34), just to mention a few. 



Along "biomineralogical" lines much re- 

 search has been conducted on such subjects 

 as mineral dust (35, 36) and its concentra- 

 tion in lung tissue (37, 38) ; and the structure 

 and chemical resistance of apatite tooth 

 enamel (39, 40). Diatoms with their intricate 

 structures have long been a fa\'orite subject 

 of microscopists (41, 42), and high magnifi- 

 cation studies of their structures and mode 

 of occurrence in diatomaceous earth are of 

 academic and industrial importance. Studies 

 of coal surfaces have revealed structures, 

 such as those shown in Figure 8, which are 

 presumably of botanical origin. 



Surface Features of Minerals and Min- 

 eral Aggregates 



The development of replica techniques 

 opened the way to the study of mineral 

 structures which either were not well repre- 

 sented or could not be observed on or in 

 mineral fragments. Study of fracture sur- 

 faces of crystals or fragments of single min- 

 erals provides evidence about such features as 

 cleavage, fracture patterns, and inclusions 

 (43, 44, 45, 46) ; whereas in compomids, ag- 

 gregate textures, morphology and relative 

 hardness of mineral components, and the 

 amount and role of cementing material can 

 be evaluated. External surfaces yield data 

 on features produced during growth or by 

 subsequent physical or chemical action under 

 conditions imposed by nature or man. This 

 area of study penetrates many branches of 

 science and thousands of electron micro- 

 graphs of mineral materials appear through- 

 out the scientific literature of the miner- 

 alogist, chemist, physicist, soil scientist, 

 ceramist and engineer. Surface changes on 

 catalysts (47), the abrasion of diamond (48), 

 oxidation of sulfides (49), dislocations in 

 crystals (50, 51), grain growth at high tem- 

 peratures (52), nucleation of ice crystals (53), 

 epitaxial relationships (54), gliding, twin- 

 ning, scratches: all these and many more 



192 



