The Cr²⁺-O and Cr³⁺-O bond lengths in CaO-MgO-Al₂O₃-SiO₂ glasses containing ~0.3 wt% Cr with Cr²⁺/ΣCr = ~ 1 or 0 (where ΣCr = Cr²⁺ + Cr³⁺) were determined by extended X-ray absorption fine structure (EXAFS) spectroscopy to be 2.034(5) and 1.967(7) Å, respectively. The Cr²⁺-O bond length is consistent with square planar coordination and the Cr³⁺-O bond length with octahedral coordination. These bond lengths were used to calculate force constants of 1206(9) Nm⁻¹ for Cr²⁺-O and 2001(21) Nm⁻¹ for Cr³⁺-O in silicate melts. The value for Cr³⁺-O is similar to previous estimates but that for Cr²⁺-O is almost 20% lower. The force constants were used to calculate the difference in Cr isotopic composition (Δ⁵³Cr) between both olivine and melt and spinel and melt for MORB with equal amounts of Cr²⁺ and Cr³⁺ at 1150 °C. The resulting values, Δ⁵³Cr_ol-mlt = −0.050(4) and Δ⁵³Cr_spl-mlt = 0.087(4), are larger by ~0.03 than those obtained using CrO bond lengths estimated from ionic radii. For Δ⁵³Cr_spl-mlt this difference is equivalent to a change in temperature of over 300 °C at constant Cr²⁺/ΣCr. The fractionation of Cr isotopes in ocean island basalts should be larger for fractional crystallisation in the crust than partial melting in the mantle due to the strong negative effect of pressure on Cr²⁺/ΣCr. The new bond length data for Cr²⁺-O provide an additional constraint for modelling and interpreting Cr isotope fractionation during igneous petrogenesis.

CaO-MgO-Al ₂ O ₃ -SiO ₂玻璃中的 Cr ²⁺ -O 和 Cr ³⁺ -O 键长含有 ~0.3 wt% Cr，Cr ²⁺ /ΣCr = ~ 1 或 0（其中 ΣCr = Cr ^{2 +} + Cr ³⁺ ) 通过扩展 X 射线吸收精细结构 (EXAFS) 光谱测定分别为 2.034(5) 和 1.967(7) Å。Cr ²⁺ -O 键长与正方形平面配位一致，Cr ³⁺ -O 键长与八面体配位一致。这些键长被用于计算的1206（9）的力常数牛顿米^-1对Cr ²⁺ -O和2001年（21），牛米^-1对Cr硅酸盐熔体中的³⁺ -O。Cr ³⁺ -O 的值与之前的估计值相似，但 Cr ²⁺ -O 的值几乎低 20%。对于具有等量 Cr ²⁺和 Cr ^{3+ 的}MORB，在 1150 °C 时，力常数用于计算橄榄石和熔体以及尖晶石和熔体之间Cr 同位素组成 (Δ ⁵³ Cr) 的差异。所得值 Δ ⁵³ Cr _ol-mlt  = -0.050(4) 和 Δ ⁵³ Cr _spl-mlt  = 0.087(4) 比使用根据离子半径估计的Cr O 键长获得的值大 ~0.03 。对于 Δ ⁵³ Cr _spl-mlt这种差异相当于在恒定的 Cr ²⁺ /ΣCr下温度变化超过 300 °C 。由于压力对 Cr ²⁺ /ΣCr的强烈负面影响，海洋岛玄武岩中 Cr 同位素的分馏对于地壳中的分步结晶应大于地幔中的部分熔融。Cr ²⁺ -O的新键长数据为模拟和解释火成岩成因过程中的 Cr 同位素分馏提供了额外的约束。