A series of coesite, coexisting with or without a liquid phase, was synthesized in the nominal system SiO₂-H₂O at 800−1450 °C and 5 GPa. Micro-Raman spectroscopy was used to identify the crystalline phase, electron microprobe and LA-ICP-MS were employed to quantify some major and trace elements, and unpolarized FTIR spectroscopy was applied to probe the different types of hydrogen defects, explore water-incorporation mechanisms and quantify water contents. Trace amounts of Al and B were detected in the coesite. Combining our results with the results in the literatures, we have found no positive correlation between the Al contents and the “Al”-based hydrogen concentrations, suggesting that previously proposed hydrogen-incorporation mechanism H⁺ + Al³⁺ ↔ Si⁴⁺ does not function in coesite. In contrast, we have confirmed the positive correlation between the B contents and the B-based hydrogen concentrations. The hydrogen-incorporation mechanism H⁺ + B³⁺ ↔ Si⁴⁺ readily takes place in coesite at different P-T conditions, and significantly increases the water content at both liquid-saturated and liquid-undersaturated conditions. For the SiO₂-H₂O system, we have found that type-I hydrogarnet substitution plays a dictating role in incorporating water into coesite at liquid-saturated condition, type-II hydrogarnet substitution contributes significantly at nearly dry condition, and both operate at conditions in between. The water solubility of coesite, as dictated by the type-I hydrogarnet substitution, positively correlates with both P and T, $c_{{\text{H}}_2\text{O}}$ = −105(30) + 5.2(32) × P + 0.112(26) × T, with $c_{{\text{H}}_2\text{O}}$ in wt ppm, P in GPa and T in °C. Due to its low water solubility and small fraction in subducted slabs, coesite may contribute insignificantly to the vertical water transport in subduction zones. Furthermore, the water solubility of any coesite in exhuming ultra-high pressure metamorphic rocks should be virtually zero as coesite becomes metastable. With an adequately fast water-diffusion rate, this metastable coesite should be completely dry, which may have been the key factor to the partial preservation of most natural Coe. As a byproduct, a new IR experimental protocol for accurate water determination in optically anisotropic nominally anhydrous minerals has been found. Aided with the empirical method of Paterson (1982)Paterson (1982) it employs multiple unpolarized IR spectra, collected from randomly-orientated mineral grains, to approximate both total integrated absorbance and total integrated molar absorption coefficient. Its success relies on a high-level orientation randomness in the IR analyses.

在800-1450°C和5 GPa的标称体系SiO ₂ -H ₂ O中合成了一系列有或没有液相的共沸石。用显微拉曼光谱法鉴定结晶相，用电子探针和LA-ICP-MS定量分析一些主要和痕量元素，并用非极化FTIR光谱法检测不同类型的氢缺陷，探索水的结合机理并量化水含量。在余辉岩中检测到痕量的Al和B。将我们的结果与文献中的结果相结合，我们发现Al含量与基于“ Al”的氢浓度之间没有正相关关系，这表明先前提出的氢结合机理H ⁺ + Al³⁺ ↔Si ⁴⁺在堇青石中不起作用。相反，我们已经证实了B含量和基于B的氢浓度之间呈正相关。氢结合机理H ⁺ + B ³⁺ ↔Si ⁴⁺容易在不同的P - T条件下在堇青石中发生，并显着增加了液体饱和和液体不饱和条件下的水含量。对于SiO ₂ -H ₂在系统中，我们发现I型氢石榴石的取代在液态饱和条件下将水掺入钙矾石中起着决定性的作用，II型氢石榴石的取代在接近干燥的条件下起着重要作用，并且两者都在两者之间的条件下运行。由I型氢石榴石取代所决定的堇青石的水溶性与P和T均呈正相关，$C_{{\text{H}}_2\text{Ø}}$= −105（30）+ 5.2（32）× P + 0.112（26）× T，其中$C_{{\text{H}}_2\text{Ø}}$以wt ppm为单位，以GPa为单位的P和T以°C为单位。由于其水溶性低，且在俯冲板块中所占的比例很小，所以堇青石可能对俯冲带中的垂直水输送没有明显的作用。此外，在膨化超高压变质岩中，任何堇青石的水溶性几乎都应为零，因为它变成了亚稳的。在足够快的水扩散速度下，这种亚稳态的堇青石应完全干燥，这可能是大多数天然Coe部分保存的关键因素。作为副产品，已经发现了一种新的IR实验规程，用于准确测定光学各向异性的名义无水矿物中的水分。借助Paterson（1982）和Paterson（1982）的经验方法，它采用了多个非偏振红外光谱，这些光谱是从随机取向的矿物颗粒中收集的，估算总积分吸光度和总积分摩尔吸收系数。它的成功依赖于IR分析中的高级定向随机性。