The fourth mechanism involves instances where small crystals come together and fuse in a specific, orientation-dependent manner to form a larger crystal (Extended Data Movie 4). This process differs from the more common random aggregation leading to polycrystalline structures; here, the particles align according to their crystallographic axes before merging, thereby maintaining a common crystallographic orientation across the newly formed, larger crystal. During these oriented attachment events, we frequently observe the melting and subsequent re-crystallization of the contact region between the two crystals. This process, which facilitates the proper alignment of the crystals, results in a flawless area, completely eliminating the seam that initially separated the two structures (Fig. ).