The Stone of the Ruins of the Chapel of San Isidoro and San Pelayo (El Retiro, Madrid)

Abstract The ruins of the Chapel of San Isidoro and San Pelayo were relocated to the Retiro Park from Avila at the end of the 19th century, with the aim of preserving them. Caleña stone is the main construction material. This Stone is characterized by its geological formation process, resulting in three varieties: white, ochre and red. The environmental conditions and the anthropic pressure to which the monument is subjected have accelerated its already advanced decay, causing further alteration of the material. Five samples are characterized using a multidisciplinary approach, combining the techniques of X-ray diffraction (XRD), polarized optical microscopy (POM) and scanning electron microscopy with microanalysis (SEM-EDX). Also, physical constants are analysed by determinating their bulk density (𝜌𝑏), absorption coefficient (AC) and open porosity (𝑝𝑜). The data obtained from the characterization allow a greater knowledge of the building material of the Chapel, contributing to the understanding, prevention and conservation of this unique monument, providing a deep knowledge of the stone.