The oxidation state of Cr, Cr²⁺/ΣCr (where ΣCr = Cr²⁺ + Cr³⁺ = 0.35 wt%), in Fe-free silicate glasses quenched from melts equilibrated as a function of pressure to 3.5 GPa at 1500 °C, and as a function of temperature to 1500 °C at atmospheric pressure, and at oxygen fugacities (fO₂, in log units relative to the quartz-fayalite-magnetite (QFM) buffer) between ∆QFM = − 1 and − 2, was determined by XANES spectroscopy. Increasing temperature stabilises Cr²⁺ and increasing pressure stabilises Cr³⁺. A general expression for Cr³⁺/Cr²⁺ in silicate melts was derived: log(Cr³⁺/Cr²⁺) = 1/4(∆QFM + 8.58 − 25,050/T + 940P/T − 0.02P) + 9770/T − 7.69 + 6.22Λ + (900P − 172P²)/T, where P is pressure in GPa, T is temperature in K, and Λ is the optical basicity of the composition. This equation reproduces 213 Cr²⁺/ΣCr values reported here and in the literature with an average ΔCr²⁺/ΣCr of 0.02. A MORB melt at 1400 °C and QFM is predicted to have Cr²⁺/ΣCr ~ 0.35 at the surface but Cr²⁺/ΣCr ~ 0 at a depth of ~ 60 km. Although Cr²⁺ is an important oxidation state in silicate melts it is not preserved at low temperatures due to an electron exchange reaction with Fe³⁺.

无 铁硅酸盐玻璃中的Cr，Cr ²⁺ /ΣCr（其中ΣCr= Cr ²⁺  + Cr ³⁺ = 0.35 wt％）的氧化态在1500°C下由压力平衡至3.5 GPa的熔体淬火后的无铁硅酸盐玻璃，以及在大气压力和氧气逸散度（f O ₂，相对于石英-铁橄榄石-磁铁矿（QFM）缓冲液的对数单位）到∆QFM = − 1和− 2时的温度的函数。用XANES光谱法测定。温度升高使Cr ²⁺稳定，压力升高使Cr ³⁺稳定。得出了硅酸盐熔体中Cr ³⁺ / Cr ^2+的一般表达式：log（Cr ³⁺ / Cr²⁺）= 1/4（∆QFM + 8.58-25,050 / T  + 940 P / T  -0.02 P）+ 9770 / T  -7.69 +6.22Λ+（900 P  -172 P ²）/ T，其中P为压力在GPa中，T是在K中的温度，并且Λ是组合物的光学碱度。该公式可重现此处和文献中报道的213 Cr ²⁺ /ΣCr值，平均ΔCr2 ⁺ /ΣCr为0.02。甲MORB熔体在1400℃下和QFM被预测为具有铬²⁺ /ΣCr〜0.35在表面，而且铬²⁺ /ΣCr〜0在〜60公里的深度。虽然铬²⁺是硅酸盐熔体中的重要氧化态，由于与Fe ³⁺发生电子交换反应，因此在低温下无法保存。