A general term that implies either the region between the two adjacent layers or the relation between the two adjacent layers (quot Guggenheim et al., 2009). “Interlayer distance” is more precise to describe the distance between the adjacent layers (tetrahedral sheet to tetrahedral sheet, as shown in Fig. 2), and is measured by taking the average of the z coordinate of the basal oxygen plane. The “interlayer displacement” describes the displacement portion or lateral shift from tetrahedral sheet to tetrahedral sheet across the interlayer space. Cf., layer, layer displacement

For phyllosilicates, interlayer material separates the 1:1 or 2:1 layers and generally may consist of cations, hydrated cations, organic material, hydroxide octahedra, hydroxide octahedral sheets (see fig. 2), and/or hydroxy-interlayers as a combination of H₂O and hydroxyl-coordinated cations. The interlayer material offsets the net negative charge of the layer. In certain cases (e.g., talc, pyrophyllite, where the net layer charge is zero), there is no interlayer material, and an interlayer separating the layers is empty. After Guggenheim et al. (2006). Cf., layer; hydroxy-interlayer

abbreviated from interlayer-cation-deficient mica (Rieder et al., 1998). A group name for platy phyllosilicates of 2:1 layer and a layer charge of between -0.6 to -0.85 per formula unit. Interlayer-deficient micas do not have swelling capacity. The subgroups of the brittle micas are based on dioctahedral or trioctahedral character (wonesite is the only known member of the trioctahedral subgroup), and species within the subgroups are based on chemical composition. The value of -0.6 is a general limit, as wonesite appears to be an exception with a layer charge of -0.5, although it has no swelling capacity. The value of -0.85 has been fixed from examples of dioctahedral species only. Previous to Rieder et al. (1998), the term “hydromica” was used to express a perceived excess in H₂O above the O₁₀(OH)₂ formula unit, but these phases are either interstratifications (e.g., hydrobiotite = interstratification of biotite and vermiculite) or micas that exhibit a deficiency in interlayer cation occupancy. Thus, the term “hydromica” was abandoned in favor of interlayer-deficient mica. The term for species “hydrobiotite” was confusing, and the use of the prefix “hydro” is now avoided. Cf., mica, true mica, brittle mica, group names

a concept introduced by Nadeau et al. (1984) which theorizes that individual clay mineral particles of oriented samples used in X-ray diffraction studies are stacked in aggregated composite particles which coherently scatter radiation so as to give rise to 00l diffraction patterns similar to those of uncleaved McEwan crystallites. The composite particles are theorized to be produced during sample preparation following disaggregation of original rock or soil samples.

a clay material where two or more kinds of layers are interleaved in a coherently diffracting structural domain with a degree of ordering which may vary from random to completely ordered. Layers may be 1:1 layers or 2:1 layers and interlayers may be of swelling or non-swelling nature. X-ray diffraction and transmission electron diffraction (TEM) are two common techniques used to determine layer proportions and regularity of interleaving. Energy dispersive techniques are commonly used to obtain chemical information. Regular interstratifications may be designated as mineral species, provided that they conform to specific criteria as specified by the International Mineralogical Association. Non-regular interstratifications are commonly characterized according to the information available, e.g., mica-smectite irregular interstratification, and do not warrant species status.

Intracrystalline swelling involves an increase in the layer-to-layer spacing of a phyllosilicate mineral to accommodate H₂O or other molecules in the interlayer. For example, in swelling clays, an increase in the relative humidity around the clay mineral particle, causes interlayer expansion, resulting in partially or fully hydrated interlayer ions. Cf., osmotic swelling

a stability constant, K, for a complex is determined from the activity of the complex in solution divided by the activity of the reactants in a system at equilibrium. The larger the value of K, the greater is the stability of the complex. For multiple complexes that may result in a reaction, several constants may be determined, thus K_overall is the product of multiple constants: K₁ x K₂ x K₃… >Intrinsic= is used because the stability constant is an essential physical chemical parameter that relates concentrations of the components of a reaction at equilibrium.

an irreversible expansion of a solid upon rapid heating. Interstratified mica-vermiculite commonly shows expansion upon rapid heating owing to the loss of interlayer H₂O at relatively low temperatures. The separation of the locally collapsed layers (interstratified mica) increases the pressure locally, inhibits H₂O outgasing, leading to expansion, which produces worm-looking threads (Hillier et al., 2013). According to Grim (1968), Web (1824) first used the term vermiculite (the sample was probably impure with interstratified mica-vermiculite) because samples produced the wormy threads, and it is this characteristic that gives the vermiculite group its name: vermiculari, to breed worms, in Latin. As expected, Hillier et al. found that pure vermiculite (no interstratified mica present) does not show the wormy threads when rapidly heated. See vermiculite

Atoms or molecules become ions by the gain or loss of electrons, which have a negative charge. A positively charged ion, or cation, involves a loss of one or more electron(s). A negatively charged ion, or anion, involves a gain of one or more electron(s).

a fluxional bond formed between an ion and a polar molecule. The classic example is where water molecules hydrate a sodium cation. However, the interaction is not restricted to H₂O, as many polar organic molecules will form ion-dipole interactions. See fluxional bond.