By analogy with dislocation glide, a Schmid factor criterion was often used in the case of twinning. The deformation textures of extruded AM30 Mg alloy tubes deformed along different directions showed clear evidence that extension twinning was responsible for the texture changes and that its activation was dictated by the Schmid factors applicable to different twinning planes. The rules for the selection of the twin variants in the present case were particularly well defined because of the sharp texture of the starting material.Use of Schmid Factors to Select Extension Twin Variants in Extruded Magnesium Alloy Tubes. S.Godet, L.Jiang, A.A.Luo, J.J.Jonas: Scripta Materialia, 2006, 55[11], 1055-8