Hydroxy-interlayered vermiculites are 2:1 layer phyllosilicates with a permanent layer charge of 0.6 – 0.9 per formula unit and with fixed complexes in the interlayer. 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 vermiculite and hydroxy-interlayered vermiculite is poorly defined. Vermiculite and HIV phases are often interstratified.
See hydroxy-interlayered mineral.
Cf., hydroxy interlayer, hydroxy interlayering, hydroxy-interlayered smectite, smectite, vermiculite