Clarify the basis of the previously reported anorthite twinning CRSS

Establish how the approximately 100 MPa critical resolved shear stress previously reported for twinning in millimeter-sized plagioclase single crystals was derived, given that multiple deformation mechanisms operated during those experiments.

Background

The paper compares its micropillar-derived twinning stress with an earlier estimate obtained from deformation experiments on millimeter-sized plagioclase single crystals. Those earlier experiments involved twinning together with other deformation mechanisms, making the attribution of the measured stress specifically to twinning uncertain.

Clarifying the derivation of the earlier value is important for extrapolating micropillar results to natural grain sizes and for evaluating proposed size effects in anorthite twinning.