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NOTICE: This is an OSHA Archive Document, and no longer represents OSHA Policy. It is presented here as historical content, for research and review purposes only.

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IR image
The second most common method of analyzing crystalline silica is based on the absorption of infrared light. Compared to XRD, IR is a less expensive method choice when interferences are known and can be compensated for. The IR method is used by the Mine Safety and Health Administration (MSHA) for Coal Mining samples.

The tetrahedral SiO2 structural units absorb light frequencies at characteristic vibrations. One isolated tetrahedral unit is illustrated to the right. Note that though each silicon atom is surrounded by four oxygen atoms, each oxygen is also associated with other silicon atoms so that the ratio of two oxygen atoms for each silicon atom is maintained in the crystal structure.

Analytical methods developed by recognized authorities provide a basis for individual laboratory procedures. A summary of and access to accepted methods is provided.
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