THE study of non-clay minerals in clays is very important, both industrially and scientifically. Because of the influence of these minerals on the properties of clays, even when they occur in small amount as fine-grained particles dispersed throughout the clay, it is usually desirable to identify them, to estimate their particle size and distribution, and to observe their morphology. The study of minerals constituting dusts is also very important and here the quantity of the original sample available is often extremely limited.
For such investigations electron-optical methods have some distinct advantages over others. Among recent developments high-resolution, powder, or selected-area electron-diffraction patterns and dark-field images from Bragg reflections (Talbot, 1956) are especially effective for the identification of mineral particles because they can clarify morphological characteristics as well as the details of crystal structure for each small crystal.
Electron-optical data for minerals that are likely to be found in close association with clays are given below. More electron-optical information on other non-clay minerals may be found in the publications of Gorbunov (1957), Bates (1958, 1961), Gritsaenko, Rudnitskaya, and Gorshkov (1961), Rekshinskaya (1966), and Beutelspacher and van der Marel (1968).