Different morphologies were identified from the different grades; A1 – Elongated hexagonal morphology as deduced, A2 – Size distribution of the elongated hexagonal morphology, B1 – regular hexagonal morphology, B2 – Size distribution of the regular hexagonal morphology, C1 – rhombohedral morphology, C2 – Size distribution of the rhombohedral morphology, D1 – cubic morphology, D2 – Size distribution of the cubic morphology.