ATOMIC-FORCE MICROSCOPY INVESTIGATIONS ON LIBYAN DESERT GLASS AND OTHER SILICA GLASSES OF DIFFERENT ORIGINS

Several glasses of high- and low-temperature origin were compared with Libyan Desert Glass (LDG) using the atomic force microscope (AFM). Th e high-temperature glasses studied were Suprasil 300, Suprasil 300 OH- free, and Herasil. The low-temperature glasses were colourless preciou s opal, SiO2 gel-coated microscope slides, and bulk SiO2 sol gel glass . All samples except the coating were fractured before imaging to obta in clean, new surfaces. On the 1 mu m(2) AFM images, the LDG fracture minor zone with a typical root mean square (RMS) roughness of 0.5 nm i s rougher than the surface of the coating (RMS = 0.3 nm) and comparabl e to the Suprasil fracture mirror zone (RMS = 0.6 nm). The fracture su rfaces can be described by two types of outcrops. Type A outcrops with diameters of a few 10 nm were found on Suprasil and Herasil, type B o utcrops with diameters between 100 and 200 nm on bulk sol-gel glass an d opal. The clear LDG had type A outcrops, the opaque LDG showed both types. Pores and a cluster-like nanostructure were evident in the bulk sol-gel glass. Crystals were found on X-ray amorphous Herasil and pre cious opal. None of these features was discovered on those LDG samples which were visually free of inclusions.