PETUOGRAPIIIC THIN SECTIONS 



Freund, H., "Handbuch der Mikroskopie in der 

 Technik," Vol. II, Umschau Verlag, Frank- 

 furt, a. M., 1954. 



Jaffe, H. W., "Application of the Rule of Glad- 

 stone and Dale to Minerals'-, Am. Miner- 

 alogist,^!, 757-777 (1956). 



Larsen, E. S. and Berman, H., "The Microscopic 

 Determination of the Nonopaque Minerals," 

 U.S. Geological Survey, Bull. 848, 1934. 



MooREHousE, W. W., "The Studj- of Rocks in 

 Thin Section," Harper and Bros., N.Y., 1959. 



Short, M. N., "Microscopic Determination of the 

 Ore Minerals," U.S. Geological Survey, Bull. 

 914, 1940. 



Wahlstrom, E. E., "Optical Crystallography," 

 3rd Ed., John Wiley and Sons, N. Y., 1960. 



WiNCHELL, A. N. AND WiNCHELL, H., "Elements 

 of Optical Mineralogy, Pt. II," "Descriptions 

 of Minerals," John Wiley and Sons, N.Y., 

 1951. 



Ernest E. Wahlstrom 



PETROGRAPHIC THIN SECTIONS 



The industrial chemist often has to deal 

 with hard or brittle solids which are essen- 

 tially transparent. In the microscopy of such 

 solids, the ground thin sections developed 

 by the petrographer for the stud}^ of rock 

 specimens (1) may be used to good advan- 

 tage, either alone or in conjunction with other 

 sampling methods (2). Such thin sections are 

 particularly useful in developing the follow- 

 ing information: number and population of 

 the various species which are present; the 

 structure of the specimen and the spatial 

 distribution of the entities of which it is 

 composed; evidences of physical and chem- 

 ical changes which have occurred in the 

 specimen; microscopic characteristics of the 

 specimen in specific orientation. 



Typical industrial materials which are 

 well adapted to thin section microscopy are: 

 abrasive wheels, coal, charcoal, ceramics, re- 

 fractories, clinkers and slags, glass, resins, 

 scales and deposits, pelleted and molded 

 materials, catalysts, caked and cemented 

 solids, and solid raw materials. Literature 

 references to several of these applications 

 are given by Chamot and Mason (2). 



The petrographer's standard procedure 

 for thin section preparation involves the fol- 

 lowing basic steps: preparation of a slice or 

 chip of suitable area and i^ inch or less in 

 thickness; grinding of one side of the slice 

 to provide a smooth, though not polished, 

 surface; cementing of the smooth surface to 

 a glass slide; grinding of the other side of the 

 slice with progressively finer abrasive until 

 the desired thickness (usually .02-.03 mm) 

 is reached and the free surface is smooth; 

 cementing of a cover glass on the section 

 unless it is desired to polish the surface and 

 combine polished section and thin section 

 microscopy in the same slide (3). Poorly con- 

 solidated materials are embedded in a suit- 

 able resin before grinding and either water 

 or a hydrocarbon, depending on the solu- 

 bility characteristics or the specimen, is used 

 as a grinding lubricant. Typical basic equip- 

 ment includes: a diamond or carborundum 

 saw, a variable speed mechanical grinder 

 with interchangeable lapping plates for 

 coarse and fine abrasives, a flat glass plate 

 for fine lapping, and an adjustable hot plate 

 or oven. Rogers and Kerr (1) describe these 

 techniques in detail and Chamot and Mason 

 (2) list a wide variety of modern cementing 

 and embedding media. 



The petrographer's standard procedures 

 may usually be applied to anj^ thermally 

 stable industrial materials. Modification, as 

 dictated by the specific case, is required for 

 extension to organic and thermally unstable 

 inorganic samples. This involves specific 

 choice of the combination of cementing and 

 embedding media, abrasive, lubricant and 

 general conditions based on the chemist's 

 knowledge or best guess concerning the inter- 

 action of these factors with the sample. For 

 instance, excessive temperatin-es must be 

 avoided during grinding and handling of the 

 specimen and a lubricant must be chosen 

 which will not dissolve it. Thin sections of 

 samples which are soft enough to retain 

 abrasive during the customary w^et grinding 

 but which, for any reason, may not be sec- 



473 



