Mineral Geothermometer
A secondary mineral phase whose stability is defined by a lower and sometimes an upper temperature threshold. Common mineral geothermometers comprise clays, zeolites and epidote, with crystal structures that contain a hydroxyl (OH-) or water (H2O) molecule. The temperature ranges of mineral geothermometers are calibrated from investigations of a large number of drilled geothermal resources where mineral zonations and temperature gradients have been determined.