plagioclase à macle d'albite

CONT: Entre les masses biotitiques apparaissent des agrégats de plagioclases maclés albite et d'aspect trouble, auxquels s'associent de très rares cristaux de quartz et de minuscules grains d'opaques.

OBS: Plagioclase twins mechanically on the albite law. Twinning is most likely to occur when the resolved shear stress ... is at a maximum. Only those crystals oriented in the stress field to approximately meet this condition will twin. Thus, in a rock containing mechanically twinned grains, the principal stress directions affecting the rock may be approximated by measuring the twin elements of these grains.
OBS: albite-twinned plagioclase: term used at Natural Resources Canada - Earth Sciences Sector.