Because relatively little information about the crystal-growth process of smectite is available, the process was assessed here by studying the size and shape of nontronite particles synthesized at six different temperatures from 75 to 150°C over a period of 4 weeks.
The morphology of nontronites was studied using low-pressure isotherms of argon adsorption at 77 K, a method which enables the measurement of the basal and edge surface areas of the nontronite particles and of their mean diameter and thickness. During the crystal growth of nontronite, the mean particle length increased whereas their thickness (and the number of stacked layers) did not vary significantly.
A specific two-dimensional crystal-growth process was observed for smectite via the lateral extension of the layers. This process also appears to occur during the growth of neoformed natural smectite.