Crystal faces: structure and growth

Abstract

A review is given on current theories about the growth mechanisms of a crystal face. The growth depends on internal factors (crystal structure and defects) and on external factors (supersaturation, temperature and presence of impurities). Three categories of faces are distinguished, depending on the number of periodic bond chains (PBCs) present in a slice dhkl. Only F (flat) faces containing two or more PBCs can grow according to a layer mechanism. They grow slowly and are important. Other faces grow continuously and fast. Impurities adsorbed on the crystal usually retard, but sometimes accelerate the growth and may even provoke the apparition of other faces. Beyond the roughening temperature TR the flat surface structure of an F face transforms into a rough surface and the growth occurs continuously and is faster. TR becomes lower when the interaction between crystal and fluid increases. The growth rate of an F face increases when the attachment energy of a new layer is higher. This allows to define a theoretical habit as exemplified for fluorite, quartz, olivine, feldspar, dolomite and calcite.