542 Annals New York Academy of Sciences 



to the flaky mineral, a few opaque and equidimensional particles were also 

 visible. These were probably octahedral or dodecahedral crystals of magnetite. 

 Their average diameters were 0.2 to 0.5 fi. 



X-ray and Electrott Diffraction Studies 



X-ray and electron diffraction techniques were used to identify the mineral 

 matrix of the Orgueil meteorite. The x-ray data were obtained from diffrac- 

 tometer patterns, from manual, step-scanning counts, as well as from flat film 

 and Debye-Scherrer photographs. 



The 6 meteorites, (including 2 Orgueil samples, A and C), were x-rayed. In 

 addition, x-ray patterns were obtained from a sample of salt, extracted with 

 water from Orgueil, from 5 samples of Orgueil heated with water in sealed glass 

 tubes for a period of several days at 105°, 240°, 350°, and 400° C, respectively, 

 and, from samples of Orgueil, Murray, and Holbrook, after being subjected to 

 rapid heating in air to 980° C. temperature. The results were compared with 

 published data and with the diffraction patterns of the following standards: 

 chlorite (clinochlore) from Brinton Quarry, West Chester, Pa.; magnetite from 

 Mineville, Adirondack Mts., N.Y. (both were obtained from the Mineral 

 Collection of the Department of Geology, Columbia University); serpentine 

 (mainly antigorite) from Havana, Cuba (from the Genth Collection, The 

 Pennsylvania State University), and iron (metal) powder, C.P. grade. 



The carbonaceous chondrites gave poor diffraction patterns. Apparently, 

 this was caused by small particle size and by a strong fluorescence of the sample, 

 when subjected to CuKa radiation. Magnetite lines appeared on all Orgueil 

 patterns; many of the silicate lines were made visible on photographic film by 

 reducing the exposure of the diffuse background with another strip film, put in 

 front of the one that was to be used for the diffraction record. Manual, step- 

 scanning in the low angle region established a diffuse band related to the char- 

 acteristic basal reflections of layer lattice silicates. The counting pattern, 

 however, did not show the same resolution as the photographs, where at least 

 one of the 001 reflections stood out as a very weak but as a still shghtly notice- 

 able line. The hydrothermal treatment of Orgueil failed to improve the 

 quahty of the diffraction effects. 



Diffraction data from the Orgueil sihcates are shown in table 4, with some 

 layer lattice silicates containing magnesium. Low angle counts obtained from 

 oriented slides are shown in figure 2. The oriented samples were prepared by 

 subjecting the powdered meteorite to shearing stress with a pestle on abraded 

 glass slides. This produced a thin, glossy film in which the mineral flakes 

 appear to have been aligned parallel to the glass, as prescribed by earlier experi- 

 ments and theory.-^ Each 0.2 degree 26 increment was counted in the 2.0°- 

 16.0° 2d range for a period of 134 seconds, with CuKa radiation and a scale 

 factor of 256 on a Norelco X-ray diffractometer unit. The statistical probable 

 error in the counts, under such experimental conditions, is 0.4 per cent. 



Because of the uncertainty in the position of the 001 reflections positive 

 identification was not possible. Chlorite and/or montmorillonite may be 

 present; the former is a likelier constituent, considering that chlorites rich in 

 iron give weak 1st and 3rd order basal reflections. Reflections extending above 

 7 A preclude serpentine. 



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