Changes on the surface properties of foliated marbles at different cutting orientations

Abstract

A single calcite crystal shows a pronounced anisotropy that can be transferred to the bulk stone, especially in the case of marbles. The aim of this paper is to analyse the effect of the preferential crystallographic orientation of the anisotropic calcite crystals on the surface properties of foliated marbles. Variations of microhardness, roughness, solubility and contact angle in rock surfaces are studied taking into account their relative position with respect the metamorphic foliation. Results show that more than 50% of the crystals have their c-axis oriented close to the normal of the axial foliation plane. This fact has a direct response on its surface properties: i) the microhardness in surface parallel to metamorphic foliation is a 14% higher than it is in the perpendicular surface; ii) contact angle of the water on the parallel faces is slightly lower than it is on the perpendicular one (42.75° and 53.25°, respectively); and iii) a lower chemical reactivity is estimated on parallel faces, which results in a lesser roughness of weathered surfaces. Results from this paper determine the optimal direction in which an ornamental piece should be cut in order to guarantee its maximum durability.