G. Cliff1, J. A. Gard2, G. W. Lorimer1 and H. F. W. Taylor2
1 Department of Metallurgy, The University, Manchester, England
2 Department of Chemistry, University of Aberdeen, Scotland

Summary: Tacharanite has been re-examined using electron microscopy and diffraction, analytical microscopy, X-ray powder and fibre rotation photographs, and other methods. The composition approximates to Ca12Al2Si18O69H36, and the X-ray diffraction patterns can be referred to an A-centred monoclinic pseudo-cell with a 17·07, b 3·65, c 27·9 Å, β 114·1°, Z = I. In the true cell b is certainly, and a and c probably, doubled. Small, reversible changes in pseudo-cell parameters occur on heating below 200 °C, and parameters found by electron diffraction differ slightly from those found with X-rays, presumably due to shrinkage on dehydration in the high vacuum of the electron microscope. An earlier report that tacharanite changes into a mixture of tobermorite and gyrolite on standing in air is not confirmed. Tacharanite shows some important resemblances to tobermorite, but there are also significant differences.

Clay Minerals; June 1975 v. 40; no. 310; p. 113-126; DOI: 10.1180/minmag.1975.040.310.01
© 1975, The Mineralogical Society
Mineralogical Society (www.minersoc.org)