General approach for synthesizing hexagonal diamond by heating post-graphite phases.

Natural and synthetic diamonds mostly have a cubic lattice, whereas a rare hexagonal structure-known as hexagonal diamond (HD)-has been largely unexplored due to the low purity and minuscule size of most samples obtained. The synthesis of HD remains a challenge and even its existence remains controversial. Here we report the synthesis of well-crystallized, nearly pure HD by heating highly compressed graphite, which is applicable to both bulk and nanosized graphitic precursors.