- Crystals formed upon crystallization of amorphous solids are often plate shaped and contain a high density of twins. The objective of the present work was to further the understanding of the microstructure of such crystals. It is suggested that the elastic energy associated with the crystallization‐induced dilatational strains can be reduced significantly by the formation of a macroscopically invariant plane, lying parallel to the basal plane of plate‐shaped crystals. The invariant plane is obtained by means of a double‐twinning mechanism. The model accounts for continuity being maintained across the crystal‐amorphous matrix interface in spite of the volume change involved in the crystallization. The situation bears close resemblance to that dealt with by the crystallographic theory of the martensitic transformation.