Hydroxy-interlayered smectites are 2:1 phyllosilicates with a permanent layer charge of approx. 0.2 – 0.6 per formula unit and with fixed interlayer complexes. These complexes are composed of cations, mainly Al³⁺, but possibly Mg²⁺ and Fe³⁺, octahedrally coordinated by H₂O and OH^–. Presumably, the high-charge Al³⁺ fixes the complex, which thus limits swelling or shrinking capabilities. Depending on the degree of hydroxy-interlayering (proportion of exchangeable cations replaced by fixed complexes), the transition between smectite and hydroxy-interlayered smectite is poorly defined. Smectite and HIS phases are commonly interstratified.
See hydroxy-interlayered mineral.
Cf., hydroxy interlayer, hydroxy interlayering, hydroxy-interlayered vermiculite, smectite, vermiculite