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Name Description of Technique Accuracy Remarks
Optical
microscopy
Samples are visually examined and the mineralogy is determined. Accurate to within a few percent. Requires considerable skill by analyst to identify the minerals present. Uses small samples.
Electron
microscopy
Particle composition and morphology are determined. Crystal structure is determined with transmission electron microscopy. Resolves very small particles. Accuracy limited due to the nature of the analysis. Cannot differentiate crystalline and amorphous silica except when transmission electron microscopy is used.  Methods are slow, expensive, and samples are very small.
Thermal
analysis
Measures a mineral response to temperature changes. Accurate only for quantities over 1%. Can be used only on very small samples.
Selective
dissolution
Minerals are dissolved selectively using acids.   Quartz generally is less soluble than other minerals so it remains in the residue.   The residue is analyzed to determine the content of crystalline silica. Not very accurate. Particle size and sample composition affect the accuracy of this method. Fine-grained quartz, cristobalite, and tridymite may dissolve; other minerals may not dissolve.
Separation based on density A finely ground sample is suspended in a heavy liquid. The denser minerals settle faster than less dense minerals. By varying the density of the liquid, minerals with different densities can be separated from one another. Not satisfactory for routine analysis. Particle size, shape, and surface charge affect settling rates.  The technique is slow and difficult to perform.  Many of the heavy liquids used are highly toxic.

* Taken from the Crystalline Silica Primer, Table 3 – Methods used to Detect Quartz in a Sample.
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