Silica Polymorphs
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Normally, occupational monitoring for exposure to silica begins with the
sampling and analysis for the three common polymorphs: alpha-quartz,
cristobalite, and tridymite. Tridymite is not commonly found in industrial
settings, and cristobalite is only occasionally found. About 4% of the bulk
material found in industry contains cristobalite. Approximately 8.2 million
American workers (including agricultural workers) are potentially exposed to
crystalline silica (primarily quartz) dust each year. The three polymorphs are
crystalline, that is, they have a fixed periodic pattern to their structure. In
contrast, amorphous silica has a more random molecular arrangement.
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