High resolution transmission electron microscopy evaluation of silica glaze reveals new textures

We present the first nanoscale investigation of silica glaze. High resolution transmission electron microscopy of a rock coating from the Ashikule Basin, Tibetan Plateau, reveals the presence of spheroids composed predominantly of silicon and oxygen with diameters ranging from 20 nm to 70 nm. While silica glaze spheroids co-exist with manganese-rich rock varnish in the same sample, the different rock coatings are texturally and physically distinct at the nanoscale. These observations are consistent with a model of silica glaze formation starting with soluble aluminum-silicon (Al-Si) complexes [Al(OSi(OH)(3))(2+)], mobilized with gentle wetting events such as dew or frost. The transition between complete and partial wetting on silica surfaces rests at about 20-70 nm for liquid droplets. Upon crossing this transition, a metastable wetting film would be ruptured, initiating formation of silica glaze through spheroid deposition. Copyright (C) 2010 John Wiley & Sons, Ltd.