Diamondoids were detected in the extracts of a series of coals and rocks varying in maturity, lithology, source input, and depositional environment. At the same maturity level, diamondoids are generally about a magnitude more abundant in source rocks than in coals. The concentrations of diamondoids are maturity dependent. However, while diamondoids become more abundant with the increasing thermal maturity, a diminution in diamondoid concentrations is observed at the maturity value of about Ro = 4.0% in both coals and rocks. The occurrence of diamantane destruction at 550 °C during pyrolysis suggests that diamondoids may be eventually destroyed at high temperatures in the Earth. Here we propose three main phases of diamondoid life in nature: diamondoid generation (phase I, Ro < 1.1%), diamondoid generation and enrichment (phase II, 1.1% ≤ Ro ≤ 4.0%), and diamondoid destruction (phase III, Ro > 4.0%).