Clinopyroxene thermobarometry

Compositional diagram of pyroxenes. Diopside, hedenbergite and augite are main sub-minerals of clinopyroxene. Jadeite contains aluminium and is therefore not shown in the diagram.

In petrology the mineral clinopyroxene is used for temperature and pressure calculations of the magma that produced igneous rock containing this mineral. Clinopyroxene thermobarometry is one of several geothermobarometers. Two things makes this method especially useful: first, clinopyroxene is a common phenocryst in igneous rocks and easy to identify; second, the crystallization of the jadeite component of clinopyroxene implies a growth in molar volume being thus a good indicator of pressure.

The minerals and liquids involved in clinopyroxene thermobarometry are:

• Augite - (Ca,Mg,Fe)SiO₃
• Diopside - MgCaSi₂O₆
• Hedenbergite - CaFeSi₂O₆
• Jadeite - Na(Al,Fe³⁺)Si₂O₆

References

• Putirka, Keith; Johnson, Marie; Kinzler, Rosamond; Longhi, John and Walker, David. Thermobarometry of mafic igneous rocks based on clinopyroxene-liquid equilibria, 0-30 kbar. Mineral Petrology 1996.