geothermometer

1. (geology) A proxy that allows for geothermometry, the determination of the temperature of a geological material from the past or existing at great depth.Examples: "The geothermometer is often used to calculate the deep temperatures of geothermal reservoirs on the basis of water-rock equilibrium in the exploration of geothermal resources."; "The sulphate-water geothermometer indicates that the deep hot water is at 250°C."; "The Na-K-Ca geothermometer and silica geothermometer are discussed as tools for locating and evaluating the areas prospectively valuable for geothermal development."

2. (obsolete) A thermometer designed for measuring extremely high temperatures below ground level.Examples: "Walferdin's registering thermometer and the geothermometer of Magnus are constructed on this principle."; "It is most important to notice that the experiment at Sperenberg shews that there is no regular, uninterrupted increase of temperature corresponding to the increase of depth, but that the increase of heat occurs more slowly at very great depths; in other words, that the degrees of the geothermometer grow longer as it descends."; "In England about this time the problem of constructing maximum and minimum thermometers was actively taken up. Lord Charles Cavendish first solved this question in 1757, and later in a similar way Magnus, in Berlin, for the geothermometer, and Walferdin, in Paris, by the metastatischen thermometer.”"obsolete