Analytical Methods for Measuring Water in Nominally Anhydrous Minerals

Decades of work have shown that trace- to minor-amounts of hydrous components occur in minerals whose chemical formula would be normally written without any , namely, the nominally anhydrous minerals (NAMs). When the concentrations of the components are several tenths of a percent by weight or higher, a variety of analytical such as weight loss on heating, X-ray cell parameters, X-ray structure refinement, -Fischer titrations, or even careful electron microprobe analyses can be used to establish concentrations (e.g., Aines and Rossman 1991). However, for most NAMs, accurate with these common analytical methods prove difficult if not impossible. For reason, infrared (IR) spectroscopy has become, and remains, the most widely used method detect and analyze hydrous components (OH or H_2O) in minerals and glasses because it is highly sensitive and can be done rapidly with a commonly available, modestly priced and at dimensions of just a few tens of micrometers. A change in the electric occurs when the OH bond in either water and hydroxyl ions vibrate. This motion has resonance coupling with electromagnetic radiation generally in the 3500 cm^(-1) region of the spectrum. In addition, bending motions of the water molecule, and overtones and of these motions produce absorption in the infrared.