THE CALCITE (10(1)OVER-BAR-4) CLEAVAGE SURFACE IN WATER - EARLY RESULTS OF A CRYSTAL TRUNCATION ROD STUDY

This paper introduces the application of the crystal truncation rod (CTR) technique to the study of mineral-fluid interfaces. The CTR of the calcite (10 (1) over bar 4) cleavage surface in contact with a calcite-saturated aqueous solution was measured as a function of time by using synchrotron X-ray radiation. These results are consistent with the presence of steps of monomolecular height (3.04 Angstrom high) separated by terrace areas, as observed in previous atomic force microscope studies of the calcite surface. We found that the step density decreased with time of exposure to solution, implying that the surface healed by migration and annihilation of monomolecular steps. An atomic model of the CTR measurements of the healed surface indicates that the atomic structure of the cleavage surface is not measurably different than that of (10 (1) over bar 4) crystallographic planes within the crystal and the root mean square roughness of the terrace areas between steps is 0.35 +/- 0.1 Angstrom. Higher resolution CTR measurements could reveal exact atomic positions of the calcite surface and the structure of aqueous fluids in the interfacial region.