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Flow strength measurements on major mantle silicates are even more limited than measurements on Fp. Two differential stress measurements in the DAC exist for Ca‐Pv. Shieh et al. (2004) used energy dispersive x‐ray diffraction to measure differential stress in Ca‐Pv to ~60 GPa (Figure 2.3, black open circles). Miyagi et al. (2009) used angle dispersive x‐ray diffraction to measure differential stresses to 49 GPa (Figure 2.3, black closed circles). There is a large discrepancy between these measurements, with the values of Miyagi et al. (2009) about twice as large as those of Shieh et al. (2004). In addition to potential differences in grain size, there are a couple possibilities for differences in strength measurements. Shieh et al. (2004) used a natural sample (unspecified composition), while Miyagi et al. (2009) used a synthetic starting material; thus, starting material composition could play a role. Perhaps a more likely explanation is the use of laser absorbers in these experiments. In the work of Shieh et al. (2004), Pt was mixed in the sample to use as a laser absorber. In contrast, in the work of Miyagi et al. (2009), amorphous boron was mixed with the sample. It is possible that presence of boron can artificially raise the strength of the sample through doping or pining at grain boundaries. In any case, if the values of Miyagi et al. (2009) are reflective of flow strength, then Ca‐Pv would have the highest room temperature flow strength of the major mantle silicates. However, if the measurements of Shieh et al. (2004) represent the true room temperature flow strength, then Ca‐Pv has a similar room temperature flow strength to Brg.

Figure 2.3 Summary of high‐pressure differential stress measurement on CaSiO₃ perovskite, bridgmanite and MgSiO₃ post‐perovskite. Measurements on CaSiO₃ perovskite are shown in black symbols, measurements on bridgmanite are shown in closed colored symbols, and measurements on MgSiO₃ post‐perovskite are shown with open colored symbols.