Structural and compositional anisotropy in Macael marble (Spain) by ultrasonic, XRD and optical microscopy methods

By using the non-destructive technique of ultrasonic transmission, this paper undertakes a study of the compositional and structural discontinuities in marble from Macael (Almería, Spain), which is the material of the columns in the Court of the Lions in the Alhambra (Granada, Spain), in order to contribute to understanding of the processes of deterioration and conservation affecting them. Thermal stress is responsible for alterations in the columns, and is affected by scaling, loss of substance, stains, etc. The results allow us to establish that, apart from the discontinuities in the mineralogical composition of the marble, the preferential orientation of the calcite crystals has an important effect on its anisotropic reaction. This preferential orientation is confirmed by textural studies using X-ray diffraction and determinations using a petrographic microscope equipped with universal stage.