Growth-step-selective incorporation of boron on the calcite surface

Ion microprobe analyses of as-grown{<10(1)over bar 4>} faces of B-doped cal cite single crystals show that boron oxyanions are incorporated differentia lly between nonequivalent vicinal faces that compose spiral growth hillocks . The step-selective incorporation pattern for boron anions is opposite to that observed for the tetrahedral anions SO42- and SeO42-. Independent work has shown that a tetrahedrally coordinated boron species is preferentially incorporated at the surface during growth, yet the boron in the bulk calci te is predominantly trigonally coordinated. Hence, there is a change in nea rest-neighbor coordination of boron at the surface during incorporation. A possible explanation for the step-selective incorporation of boron lies in a surface-site control over the mechanism or rate of this coordination chan ge. The findings demonstrate that multiple, structurally distinct surface a nion sites exist on calcite {<10(1)over bar 4>} faces, and inherent differe nces in these sites influence element incorporation and possibly surface ki netics. This behavior parallels the known differences for incorporation amo ng surface cation sites and further confirms that trace and minor element p artitioning is strongly affected by the structural aspects of mineral surfa ces. Such site selectivity and associated effects on potential coordination changes may be intrinsic to crystal growth and impurity incorporation. Cop yright (C) 1998 Elsevier Science Ltd.