Document qE8v4QQ6aNzwvGgej8E974OE

fi uniiinirfMi IriTi iBflidtili ;j<jL b:^^. ^ ititii U'riiVrti l 664 MICROSTRUCTURB OP CHRYSOTILB ASBBSTOS even frequently, in a particular sample, To understand the reason for the variety of growth patterns, it seems to be necessary to study the effect of impurities, lattice defect concentration etc. For synthetic chrysolite it was found that most of the fibrils had the form of hollow cylinders, and the distribution of the tilt angle of the 4-S A fringes was similar to that of natural chrysotile. The concentration of lattice defects for the direction perpendicular lo the fibre axis was not found lo be particularly different from that of natural chrysotile. Therefore, the role of impurities does not seem to be important in controlling the polytype during the growth process. It was found that most of fibrils thicker than about 350 A in diameter were discontinuous^ grown in two or three steps (Figs. 10 and 11) perhaps because of changes in the growth conditions. The diameter of the core part of these thick fibrils was of nearly the same order as the peak value of the sample whose outer diameter was sharply distributed and is in good agreement with the theoretically expected value, 260 A (Whittaker, 1957). The Tasmania sample; consisting of very short fibres, is typical of this step-growth and also shows a low frequency of appearance of the con centric lattice layer, while the Transvaal sample con sisting of long and uniform fibres, has a considerably high frequency of appearance of concentricity. It may be said on the basis of the theory of Jagodzinski St Kunze (1954) that the former sample was mainly grown by tbe radial or coupled dislocation mechanism under conditions of high supersaturation, while for the latter sample the axial dislocation mechanism prevailed under relatively low supersaturation conditions. The outer surfaces of fibrils were generally found to be very smooth and clean. This fact suggesu that the inter-fibril sites of the aggregated fibrils are generally vacant and free from any amorphous material. On the other hand, the central voids are frequently filled with amorphous material. This phenomenon may be corre lated with the mechanism of the transfer of amorphous material through the central voids by capillary ac tion. The author is indebted to Prof. T. Hibi for contin uous encouragement, to Dr E. J. W. Whittaker for valuable discussions and for critical reading of the manuscript, and also to Mr K. Shibata for experi mental assistance. The author is grateful to Prof. H. Femindcr-Moran, The University of Chicago, Mr T. Otouma, Japan Asbestos Co., Dr F. A. Mumpton, Union Carbide Corporation, Mr A. F. Wilson, Applied Mineralogy CSIRO and Prof. N. W. Noll, Bayerwcrk, for supplying the samples of chrysotile. ReJcnoeM Bates, T. F. & Come*, 1. J. (1957). Cloy and Clay Minerals, 6. 237 (Proceed. Vlth National Clay Conf.). FErnAndez-MorAn, H. (1966). trotted. tk Internal. Congr. EM* Kyoto, p. 13. Honjo, O. A Mchama, K. (1954). Acta Crytt. 7, SI 1. Jaoodzinski, H. & Kunze, 0. (1954). Ntutt Jb. Min. Mb. p. 137. Martinez, E. A Comer, J. J. (1964). Amtr. Min. 49, 133. Mumpton, F. A. A Thompson. C. S. (1967). Abstractt of Conf. thyslt and Chemistry ofAsbestos Minerals, Oxford, July 3-4,1967. Noll. W.. Kfrcker. H. A Sybektz, W. (1958). Kotioid Z. 157,1. Noll, W., Kircher, H. A Syreatz, W. (1960). Bellrage sur Mineral, und Petrographic, 7, 232. Padurow, N. N. (1950). Acta Crytt. 3,204. Whittaker, E. J. W. (1951). Acta Cryst. 4.187. Whittaker, B. J. W. (I9S5). Acta Crytt. *. 571 Whittaker, E. J. W. (I956o). Acta Crytt, 9,855. Whittaker, E. J. W. (19566). Acta Crytt. 9.862. Whittaker, E. J. W. (1956c). Acta Cryst. 9, 865. Whittaker, B. J. W. A Zussman, J. (1956). Miner. Mag. 31,107. Whittaker, B. J. W. (1957). Acta Cryst. 10,149. Yada, K. (1967). Acta Cryst. 23.704. Zussman, J., Brindley, O. W. A Comer. 3.3. (1957). Amtr. Min. 42,133. 8000 0560 ' PRODUCED BY FORD