This essay in honour of Mike Brown addresses aspects of chemical equilibrium and equilibration in rocks, with a focus on the role that chemical potentials play. Chemical equilibrium is achieved by diffusive flattening of chemical potential gradients. The idea of equilibration volume is developed, and the way equilibration volumes may evolve along a pressure–temperature path is discussed. The effect of the environment of an equilibration volume is key to understanding the evolution of the equilibration volume with changing conditions. The likely behaviour of equilibration volumes is used to suggest why preservation of equilibrium mineral assemblages and mineral compositions from metamorphism tends to occur. This line of logic then provides the conceptual support to conventional equilibrium thermodynamic approaches to studying rocks, using, for example, thermobarometry and pseudosections.

中文翻译：

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化学势的真与美

为了纪念麦克·布朗，本文着重论述了岩石中化学平衡和平衡的各个方面，重点是化学势发挥的作用。通过化学势梯度的扩散平坦化来实现化学平衡。提出了平衡体积的概念，并讨论了平衡体积沿压力-温度路径的演变方式。平衡体积环境的影响是了解平衡体积随条件变化的演变的关键。平衡体积的可能行为被用来说明为什么趋向于保持平衡矿物组合和矿物成分免受变质的影响。然后，这条逻辑线为研究岩石的常规平衡热力学方法提供了理论上的支持，