Geothermometer
A mineral or chemical property used to estimate the temperature at which a rock or crystal formed, based on elemental composition or isotopic ratios.
A mineral phase or chemical system whose composition, isotopic ratio, or physical property varies predictably with temperature, allowing geologists to infer the temperature conditions under which a rock crystallized or underwent metamorphism. Common examples include certain trace elements in zircon and feldspar compositions. Geothermometers are calibrated through laboratory experiments or natural samples of known temperature.
What this means in real life
A geologist finds ancient zircon crystals and measures their titanium content; the amount of titanium present indicates the crystal formed at roughly 800°C, revealing the temperature of the magma chamber where it grew.
What it isn’t
It is not a thermometer you can hold or read directly. It is not a single mineral, but rather a measurable chemical or physical property of minerals that scientists interpret using calibration curves to infer past temperatures.
Commonly misused online
Social media sometimes treats 'geothermometer' as if it were a precise, error-free temperature reading, when in reality all geothermometers have uncertainty ranges and require careful calibration and interpretation.
Based on 1 reference source, including primary sources. Last verified July 16, 2026.