Twin structure in the crystallite aggregation pattern

In this paper, the crystallographic relationships among all the NH₄Cl crystallites in a zigzag aggregation pattern with local anisotropy, formed under low driving force, are analysed. It is found that all the crystallites in this aggregation are twinned with one another. The anisotropy of the zigzag pattern is controlled by the twin structure. The twin structure is of 6mm symmetry. This twin structure is related to the crystal point group m3m, so it is proposed that all crystals with point group m3m (and even the similar point groups 432 and m3) have the possibility to form this zigzag pattern. It is illustrated that the crystal symmetry plays an important role in the crystallite aggregation pattern.