Document zzwLNmkaR4dbga3N41Oe8EB7a

10/08/2001 15:58 312-896-7822 SCIENCE LIBRARY PAGE 06 Fig. 3. Sample (A): natural chrytotile. (a) and (b) Dark-field and diffraction pattern- Nutice the unusually bright and undamaged internal canals; the crystal is homogeneous and undeformed A bint outline ofthe objective aperture is seen in the diffraction pattern of Fig. 3b. (c) Illustrates the blistering m a result of exposure to the beam. diffraction processes are operative: Notice that the canals are sometimes bright and sometimes dark. In the crystalline part, however, the intensity is uniform and it is clear that these fibers are free of gross deformation. Chrysotile fibers, like most sheet silicates, are beam-sensitive to 100-keV elec trons (Langer ef a/., 1974; Seshan. 1975). Precaution must therefore be exercised while obtaining the high resolution dark-field images, because upon focusing the