Abstract: The development of the morphology of baryte crystals grown in a silica gel medium is related to the changes in supersaturation. Nucleation occurs when the supersaturation in the system exceeds a threshold value which depends on the supersaturation rate, i.e. the rate at which the supersaturation is changing at the nucleation site. During growth the supersaturation decreases, although a high level of supersaturation is maintained throughout. These experimental results compare well with the morphological development predicted from theoretical models based on the periodic bond chain theory. The ontogeny of natural barytes corresponds, in considerable detail, to the experimental observations made here and strongly suggests that similarly high supersaturations have prevailed in nature. This correspondence indicates that the technique of crystal growth in a porous silica gel medium provides a good experimental model of studying natural growth processes.