Surface roughness and overgrowth dynamics: The effect of substrate micro-topography on calcite growth and Sr uptake

Abstract

Substrate roughness influences epitaxial nucleation, growth, and trace element incorporation. We qualitatively and quantitatively examine the role of calcite surface roughness on overgrowth morphology and Sr concentration. Surfaces were made by cleaving optically clear Iceland spar, then abrading calcite cleavage surfaces with sandpaper (physical weathering analogues), or by attacking the cleavage surface with dilute HCl (chemical weathering analogues). Calcite precipitated on “weathered” surfaces have morphologies that vary systematically from one substrate type to the next. Growth on the abraded substrate was shingled, didn't form a continuous growth layer, and was poorly adhered to the seed crystal. Growth on the acid etched substrate mostly formed a continuous growth layer in optical continuity with the seed crystal. Differences in overgrowth morphology are interpreted to be due to differences in island coalescence dynamics on the different substrates. Rough substrates have a high density of island nuclei per unit surface area, which inhibits island coalescence due to interfacial misfit between individual islands. In contrast, overgrowths on smooth substrates coalesced into a single crystalline overgrowth layer. There is a weak positive correlation between the initial fractal dimension of the substrate and average Sr concentration in the overgrowth.