This paper discusses the determination of the percentage of crystalline
material in a natural silica deposit which would be considered harmful to health
(<10 m). a sample of the natural silica material was recovered and split>
into a number of subsamples. Samples were sieved using a conventional dry sieve
to remove material >300 m before testing. Particle size analyses of the fine
fraction showed 75 per cent of the material was below 10 m. Initially XRD and
XPS were run on the samples to determine the minerals and composition of the
sample. The XRD revealed strong quartz peaks and smaller tridymite peaks with a
high amorphous background. The XPS indicated traces of iron, titanium and carbon
with dominant silicon and oxygen peaks. The structure of the sample was
investigated using the SEM. It was apparent that there were a number of larger
quartz crystals (>30 m) with a mix of amorphous and crystalline in the finer
fraction. It was also observed that amorphous material was attached to the
surface of the crystals. In order to determine the percentage of crystalline
quartz a known amount of quartz was added to the sample incrementally. On each
addition an XRD scan was performed and the area under the peaks recorded. Back
analysis of these peaks with an assumed percentage of crystalline material in
the original sample gave a crystalline content of 30 per cent. The quantity at
the respirable fraction was estimated to be 18.7 per cent.