Journal de Physique IV

J. Phys. IV France 118 (2004) 295-300
DOI: 10.1051/jp4:2004118034

X-ray characterisation of bulk stones from the patina to the depth stone

B. Brunet-Imbault¹, I. Rannou¹ and F. Muller²

¹ Centre de Recherche sur la Matière Divisée, UMR Université d'Orléans-CNRS, 1B rue de la Férollerie, 45071 Orléans Cedex 2, France
² Institut des Sciences de la Terre d'Orléans, UMR Université d'Orléans-CNRS, 1A rue de la Férollerie, 45071 Orléans Cedex 2, France

Abstract
The aim of this study on monumental limestone alteration is to characterise the superficial stone called patina where transformation processes due to air and water occur. We present results on stones from the Chambord castle, so Tuffeau limestone, from the Loire Valley.

Three samples has been studied and compared in relationship with their position on the monument (outside or inside).

In order to describe these samples, different techniques have been used : chemical analysis, optical microscopy. The three main phases are calcite (CaCO ₃), quartz and opal (SiO ₂), with various granulometry.

X-ray diffraction has been performed on bulk samples. A special sample holder allows to analyse very thin zones, so to describe the mineralogical composition from the epidermis to the depth stone [1]. The stones are constituted of small crystallites which differ in dimension and orientation. This conducts to a semi-quantitative description. Protecting layer of the stone is associated to the rate of dissolution of calcite in patina zone.