The residual strength is the shear resistance or the capacity of a clay, soil, or rock to withstand significant pressure that develops after strain-softening at large strains. Residual strength is controlled by the characteristics of the internal failure surface where either significant particle movements have occurred (as in soils) or the fracture interface is the peak failure surface (as in rocks). The residual strength is typically smaller than the peak failure strength of a clay, soil, or rock.

A texture visible at hand-specimen or thin-section scale in which one generation of secondary minerals or soil plasma is arranged in a net or network geometry.
See soil plasma

An obsolete term for a resinous, massive, yellow to green serpentine.

A discredited name of a material that is primarily pimelite.

See reyerite group.

Reyerite is comprised of a sheet of edge-sharing Ca octahedra with adjacent tetrahedral sheets of Si₈O₂₀ and a double tetrahedral sheet of Si₁₄Al₂O_38, and an overall chemical composition of (Na,K)₂Ca₁₄Si₂₂Al₂O₅₈(OH)₈ ^. 6H₂O (Merlino, 1988a). The tetrahedral sheets are formed from 6-fold rings of tetrahedra with some tetrahedra pointing up and some down. Na, K, and H₂O occupy partially filled sites within the double tetrahedral sheet network. Truscottite, Ca₁₄(Si₂₄O₅₈)(OH)₈ ^. 2H₂O, is similar to reyerite, but with alkali and aluminum generally absent, although a limited amount of K and Al can be present and the composition can approach reyerite. Gyrolite, Ca₁₆Si₂₄O₆₀(OH)₈ ^. (14+x)H₂O, has a Ca octahedral sheet bounded by Si₈O₂₀ tetrahedral sheets as a unit (layer charge may vary from -4 to -5 depending on Al content) separated from other similar units by an interlayer of 2Ca + Na octahedra (Merlino, 1988b). Fedorite, K₂(Ca₅Na₂)Si₁₆O₃₈(OH,F)₂ ^. H₂O, has a sheet of edge-sharing Ca octahedra with double tetrahedral sheets, Si₁₆O₃₈, on adjacent sides. Minehillite, (K,Na)₂Ca₂₈Zn₅Al₄Si₄₀O₁₁₂(OH)₁₆, has a central edge sharing Ca octahedral sheet with a single tetrahedral sheet on one side (similar to reyerite), but a complex slab that differs from reyerite on the other. The structure of cairncrossite, Sr₂Ca_7-xNa_2x(Si₄O₁₀)₄(OH)₂(H₂O)_15-x, where x is between 0 and 1, forms a unit consisting of edge-sharing Ca octahedral sheets with adjacent Si tetrahedral sheets. These units are cross linked by SrO₈ polyhedra. The structure of orlymanite (chemical composition approximately Ca₄Mn₃Si₈O₂₀(OH)₆ ^. 2H₂O), which has not been determined, is believed related to reyerite. Synthetic (“K-phase”, “Z-phase”) phases with structural similarities to reyerite are known. Reyerite group minerals are potentially important in cements used to case geothermal wells where phases form at elevated temperatures and pressures in a steam-rich environment.

The study of the deformation and flow of materials. For clay scientists, this may involve the study of the plasticity (i.e., creep, rupture) of clay, clay-water interactions, clay suspensions and interparticle forces, the electrical double layer, etc.

A property of a non-Newtonian fluid where the viscosity of the fluid increases with time at constant shear rates and shows a reduction in viscosity over time if not agitated (e.g., stirred).
Cf., Newtonian fluid, quick clay, thixotropy

See pyroxenoid group.

An obsolete varietal term for phlogopite, biotite.