Gibbs free energy, the fundamental thermodynamic potential used to calculate equilibrium mineral assemblages in geological systems, does not apply to non‐hydrostatically stressed solids. Consequently, there is debate over the significance of non‐hydrostatic stress in petrological and geophysical processes. To help resolve this debate, we consider the effects of non‐hydrostatic stress on the polymorph pairs kyanite/sillimanite, graphite/diamond, calcite/aragonite, and quartz/coesite. While these polymorphs are most relevant to metamorphic processes, the concepts developed are applicable to any single‐component solid reaction. We quantitatively show how stress variations normal to an interface alter equilibrium temperatures of polymorph pairs by approximately two orders of magnitude more than stress variations parallel to an interface. Thus, normal stress controls polymorph stability to first order. High‐pressure polymorphs are expected to preferentially nucleate normal to and grow parallel to the maximum stress and low‐pressure polymorphs, the minimum stress. Nonetheless, stress variations parallel to an interface allow for the surprising possibility that a high‐pressure polymorph can become more stable relative to a low‐pressure polymorph as stress decreases. The effects of non‐hydrostatic stress on mineral equilibrium are unlikely to be observed in systems with interconnected, fluid‐filled porosity, as fluid‐mediated reactions yield mineral assemblages at approximately constant pressures. In dry systems, however, reactions can occur directly between elastic solids, facilitating the direct application of non‐hydrostatic thermodynamics. Non‐hydrostatic stress is likely to be important to the evolution of metamorphic systems, as preferential orientations of polymorphic reactions can generate seismicity and may influence fundamental rock properties such as porosity and seismic anisotropy.

中文翻译：

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量化非静水压力对单组分多晶型物的影响

吉布斯自由能（用于计算地质系统中平衡矿物组合的基本热力学势能）不适用于非静水应力固体。因此，对于岩石和地球物理过程中非静水应力的重要性存在争议。为了帮助解决这一争论，我们考虑了非静水应力对多晶形对的蓝晶石/硅线石，石墨/金刚石，方解石/文石和石英/褐煤的影响。尽管这些多晶型物与变质过程最相关，但开发的概念适用于任何单组分固体反应。我们定量地显示了垂直于界面的应力变化如何使多晶型对的平衡温度比平行于界面的应力变化多大约两个数量级。因此，正应力将多晶型物的稳定性控制在一级。预期高压多晶型物优先于最大应力和正常应力成核，并与最大应力和低压多晶型物（最小应力）平行地增长。尽管如此，平行于界面的应力变化却带来了令人惊讶的可能性，即随着应力的降低，高压多晶型物相对于低压多晶型物可能变得更加稳定。非流体静应力对矿物平衡的影响不太可能在具有相互连接的，充满流体的孔隙度的系统中观察到，因为流体介导的反应会在近似恒定的压力下产生矿物组合。但是，在干燥系统中，弹性固体之间可直接发生反应，从而有利于直接应用非流体静力学热力学。