ABSTRACT
The technique of Polarised Light Microscopy (PLM) has long been widely used by mineralogists and geologists in the examination and identification of minerals so it makes perfect sense for this to be used for asbestos. When the surveyor takes samples for analysis, he/she needs to have at least an appreciation of the analytical procedures although competence in analysis is not needed. The method depends on the observation of a number of optical properties of the mineral fibres under polarised light. Birefringence occurs in materials where atoms are in regular arrays in a lattice type structure. The optic orientation describes whether the highest refractive index is along or across the fibre. Pleochroism is seen only in strongly coloured minerals such as crocidolite or actinolite. The refractive index of most materials is wavelength dependent usually higher refractive index at the lower wavelength or blue end of the visible spectrum. Again, in floor tiles sometimes the asbestos is very fine and well dispersed.
