Skip to main content


geothermometer An indicator of the temperature, or range of temperatures, at which a geologic event (e.g. the crystallization of a magma or the metamorphism of pre-existing rocks) occurred. Apart from the presence or absence of minerals or mineral assemblages known to be stable within certain temperature ranges, among the most widely used indicators are: (a) stable-isotope distribution, e.g. the ratios of 18O to 16O between different mineral pairs varies according to temperature (see also OXYGEN-ISOTOPE ANALYSIS); (b) mineral transformations or inversions known to be temperature dependent, e.g. the transition of α quartz to β quartz at 573°C; (c) liquid-vapour homogenization points in fluid inclusions (subject to certain assumptions, the temperature of formation of a crystal is indicated by the temperature at which the vapour bubble co-existing in the inclusion disappears upon heating); (d) unmixing or exsolution lamellae of mineral pairs below a particular temperature, e.g. chalcopyrite—bornite at 500°C; (e) temperature-dependent element distribution between co-existing minerals, e.g. iron—titanium oxide distribution between the co-existing mineral pairs magnetite—ulvöspinel and ilmenitehematite (in this instance subject also to oxygen fugacity).

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"geothermometer." A Dictionary of Earth Sciences. . 20 Sep. 2019 <>.

"geothermometer." A Dictionary of Earth Sciences. . (September 20, 2019).

"geothermometer." A Dictionary of Earth Sciences. . Retrieved September 20, 2019 from

Learn more about citation styles

Citation styles gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, cannot guarantee each citation it generates. Therefore, it’s best to use citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

The Chicago Manual of Style

American Psychological Association

  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.