AN ELECTRON-OPTICAL INVESTIGATION OF ALUMINOSILICATE CEMENTS IN SILCRETES

Silcretes developed within the in situ regolith in the Barr Smith Rang e, western Australia, were investigated using optical and electron-bea m techniques. One of the cementing agents in these silcretes showed ge l-like optical properties and had a variable aluminosilicate chemical composition at the scale of electron microprobe analysis so that it mi ght be considered as allophane-like material. High resolution transmis sion electron microscopy demonstrated that the material consists of a fine-grained and poorly ordered kaolinite embedded in a matrix of amor phous silica.