Smectite

A smectite (from Ancient Greek (smēktós)'lubricated'; from (smēktrís)'walker's earth, fuller's earth'; lit.'rubbing earth; earth that has the property of cleaning') is a mineral mixture of various swelling sheet silicates (phyllosilicates), which have a three-layer 2:1 (TOT) structure and belong to the clay minerals. Smectites mainly consist of montmorillonite, but can often contain secondary minerals such as quartz and calcite.