Crystalline silica in Mount St. Helens ash

Laser Raman spectrometry for the determination of crystalline silica polymorphs in volcanic ash

“…The total quartz and cristobalite content of the four NIOSH ash samples was found by the LRS analyses to range from 4% to 11%. These LRS data for quartz and cristobalite are in agreement with the overall results reported for other spectroscopic techniques in the recent NIOSH round-robin testing program (8,16). (The interested reader is referred to Table I in this issue's Analytical Approach article for more specific quantitative LRS results regarding the proportions of quartz and cristobalite in these ash samples.)…”

“…Unlike the IR spectra of quartz and cristobalite which contain relatively broad absorption bands at almost identical wavenumbers (9-13), the corresponding LRS spectra show sharp, well-resolved peaks. The individual spectra recorded for these two polymorphs on our LRS system are reported in another recent article in this journal (8) and consequently are not repeated in this paper. As illustrated in the spectra of Figure 1.…”

“…Our investigation into the analytical capabilities of LRS was initiated by our search for an independent method for the qualitative and quantitative determination of crystalline silica in Mt. St. Helens volcanic ash (8). A review of the available LRS literature indicated that LRS spectra were probably capable of distinguishing the three common crystalline silica polymorphs, i.e., quartz, cristobalite, and tridymite (9)(10)(11)(12)(13).…”

“…Samples Were prepared for LRS analysis by pressing approximately 300 mg of sample into 13 mm diameter pellets via the application of 200 kg/cm2 pressure in a conventional infrared pellet die (8). Spiked ash samples were mixed for 90 s in a Wig-L-Bug before being pressed into pellets.…”

Identification and characterization of individual airborne volcanic ash particles by Raman microspectroscopy

“…Furthermore, Laser Raman Spectroscopy has been applied for the characterization of Mount St. Helens (Washington) ash from the May 18, 1980. Here, besides three common crystallite silica polymorphs (i.e., quartz, cristobalite, and tridymite), Al 2 O 3 and Fe 2 O 3 have been identified [23][24][25]. Silica as well as Na Al silicate has been found by this method also in volcanic ash from Mt.…”