Microstructural modifications resulting from the dehydration of gypsum

Various faces of dehydrated gypsum-cleaved blocks and single crystals have been investigated using optical microscopy, SEM, and TEM. The orientation o f the cracks with respect to the initial gypsum structure and the Miller in dices of all possible crack planes have been determined. These crack planes have been found to be few and to correspond to planes of high atomic densi ty in the initial and final structures, therefore characterised by a low su rface tension. These observations allow us to propose cracking criteria bas ed on general concepts of crystal growth. The cracks' dimensions measured o n different faces of the pseudomorph are distributed over several orders of magnitude and seems to be self-similar. (C) 2001 Elsevier Science B.V. All rights reserved.