Collophane from the Chalk

George Brown and C. D. Ollier
Pedology Department, Rothamsted Experimental Station, Harpenden

Summary: Sixteen samples of Middle and Upper Chalk from the Chilterns yielded what appear to be fragments of fish scales, spines, and bones, which consist of collophane. X-ray examination by the powder method shows that the material has an apatite-type structure with cell dimensions close to those previously reported for francolite. Examination of single grains shows that the optical anisotropy is due to preferred orientation of the c-axes of the crystallites and this direction corresponds to the faster vibration direction. Such grains are found to be pseudouniaxial negative. Preferred orientation could not be detected in isotropic grains.

Mineralogical Magazine; December 1956 v. 31; no. 235; p. 339-343; DOI: 10.1180/minmag.1956.031.235.10
© 1956, The Mineralogical Society
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