Abstract
Surfaces of growing crystals of dolomite from Deep Springs Lake, Calif., are Ca- rich. The surfaces of the crystals have a Ca to Mg ratio in excess of 4; the surface layer is about 100A thick and approaches the composition of dolomite at its inner side. Successive fractions have been dated by C-14 and thus place a time parameter on the introduction of magnesium into the rhombohedral carbonate lattice. The crystals grow by the production of a transient surface layer which can be envisaged as a moving boundary through which the magnesium must move by solid-state diffusion with concomitant migration of calcium in the opposite direction. The formation of dolomite having a rudimentary R 3 space group takes place at the inner side of the surface layer. Crystal growth models are considered, along with implications concerning rates of growth and diffusion, solubility, and isotopic fractionations.
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