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The least common method of analyzing crystalline
silica is based in part on the differing Si-O bond strengths and densities of the various
silicas compared to the silicate minerals. While the silicas are generally uncharged
(except perhaps for SiO2 · x H2O), in silicate minerals the
tetrahedra are polarized or negatively charged relative to the positive counter ions these
minerals contain. These chemical differences affect the speed at which each mineral
dissolves in certain acids, bases, or molten fluxes. This differential solubility is often
slight so that chemical separation is sometimes incomplete. The separation is further
complicated because the rate of dissolution is related to the surface-to-volume ratio; so
small particles of the less soluble minerals sometimes dissolve faster than large
particles of more soluble minerals. This is a good and inexpensive choice for samples
that are well understood and contain either no interferences or ones that are not readily
dissolved.
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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