SMECTECH

Dioctahedral smectites have two octahedral layer types: the trans vacant and the cis vacant varieties, because one octahedral site (of three total) is vacant. Generally nontronites and beidellites are trans vacant, while most montmorillonites are cis vacant. Many smectites are composed of interstratifications of these two arrangements. Trans vacant smectites typically have higher dehydroxylation temperatures than cis vacant smectites. Powder X-ray diffraction can be used to determine the arrangements, and infrared spectroscopy can assist in quantifying site occupancies and thermal analysis is useful for estimating the degree of interstratifications.