Abstract
The different morphologies of diamond crystals reflect the growth conditions and provide valuable information about the processes that led to the formation of the diamond. Diamond twins only occur during growth and only through reticular merohedry, which has a significant effect on the physical properties of the diamond. However, due to the scarcity of samples, particularly samples with interpenetrant twins, few investigations have been conducted on their morphological features and related formation. In this article, natural diamonds with interpenetrant twins from the Republic of the Congo were analyzed to investigate the crystallographic features and related growth formation through scanning electron microscopy and micro-computed tomography. The results revealed that all of the samples exhibit cubic habits with deformation and have a rough appearance and fibrous growth layers, indicating rapid crystallization under high driving force conditions. Based on the different features of the crystals’ macroscopic morphological properties, three types of theoretical twin models are established. The cathodoluminescence imaging of the samples show that there are two patterns regarding the formation of interpenetrant twins in natural diamonds, including the origination of grains during the nucleation stage of crystals in the form of twinned positions and changes in the orientation of the growth layer arrangement during crystal growth. Moreover, a mixed type of twin structure was observed, indicating the complexity of the diamond twin growth process, involving transformation of the crystallization habit of the crystal.
