The mechanisms of the physicochemical reactions in diorite used in the construction of ancient royal Egyptian statues

Abstract

During the heights of ancient Egyptian civilization, statues of deities and pharaohs were often constructed of hard and colourful igneous rocks, such as granite and diorite. Most of these statues remain in an excellent state of preservation. However, others have unexpectedly fragmented, in some cases only a few years after having been excavated in near-perfect condition. In the present work it is shown that two interrelated physicochemical processes contribute to this degradation: (1) the infiltration of saline H2O and (2) subsequent alteration of the constituent minerals. Conclusions were reached on the basis of neutron activation and atomic absorption analyses of rock samples from two sites in Upper Egypt and leached soluble salts therefrom. These samples were identified as quartz diorites on the basis of petrographic and X-ray spectroscopic examination. The chemical significance of the geological nature of the stone is discussed. Possible precautions to be observed in the field are presented.