Chalcedony is shown by infrared and X-ray study to contain (OH) in structural sites in addition to several types of non-structural water. (OH) varies zonally; the (OH)-rich zones are more rapidly etched, have lower X-ray reflection angles, lower indices of refraction, and whiten on heating to 550-600 degrees C. Distinctive infrared absorption spectrum in the 3200 cm (super -1) to 3600 cm (super -1) region (type B); different spectrum in this region is afforded by natural quartz crystals formed at higher temperatures (type A). The structural (OH) is housed by different mechanisms in these two types of quartz, apparently depending on the structural role and availability of Al.--Modified journal abstract.

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