In geotechnical or soils engineering, the at-rest condition refers to a stress state where a soil or clay deposit is subject to three-dimensional (mutually perpendicular) stresses such that the soil/clay body only deforms vertically (i.e., along the z axis) but not laterally (i.e., along x and y axes). The ideal at-rest condition exists in a soil unit beneath a level, infinite-sized ground surface. In engineering practice, sites with level ground surface and the horizontal dimensions much greater than the vertical dimension (e.g., lake bed sediments with a horizontal surface), can be treated as an at-rest condition. For a component of soil or clay at the at-rest condition, the strains in the x and y directions are zero, and hence the vertical strain is the same as the volumetric strain (= change in volume divided by the original volume). Understanding the at-rest condition is essential for the design of structures situated on or in soil or clay.
Syn., K0 condition.

1) refers to the mineral, palygorskite, and should not be used in the mineralogic or geologic literature.
See Guggenheim et al. (2006) and references therein.

2) Attapulgite is a common, globally used industrial term synonymous with palygorskite; especially, where mined and processed in the Florida-Georgia region of the United States or other commercial deposits around the world (e.g., China, Spain, Senegal, India, Australia, Greece, Turkey and Ukraine).

A designated series of parameters (i.e., water-content properties) in geotechnical engineering used for identifying, describing, and classifying fine-grained soils and clays or loams used for (ceramic) coarse ware. These parameters, which originally included six “limits of consistency” (the upper limit of viscous flow, the liquid limit, the sticky limit, the cohesion limit, the plastic limit and the shrinkage limit) are now typically limited to the “liquid limit”, the “plastic limit” and, sometimes, the “shrinkage limit”. Atterberg limits are determined on the basis of mass of water per mass of the dry soil solid by specific test methods, as standardized by ASTM Standard D4318 – 05 or other standard tests, and expressed in percent.
See Mitchell (1993).
See also activity, consistency number, liquid limit, plastic limit, plasticity index, shrinkage limit

A common clinopyroxene with wide ranges of solid solutions, (Ca,Mg,Fe²⁺,Fe³⁺,Ti,Al)₂(Si,Al)₂O₆. Si may be replaced by Al (~ 2 to 10 mole %). Ti-bearing augite may develop sector zoning (or hourglass zoning). Exsolution lamellae of Ca-poor pyroxene in augite crystals are common. Augite occurs in mafic or ultramafic igneous rocks and in high-grade metamorphic rocks.
See pyroxene group for additional details.

Refers to rock constituents or minerals that have formed in place and were not transported. Such materials have formed either at the same time as the rock in which they are found or after the formation of the rock. The term is also applied to minerals that are clearly the result of new crystal growth on older crystals of the same kind, e.g., K-rich feldspar overgrowths may be referred to as authigenic overgrowths.

In a molecular dynamics simulation, the autocorrelation function is a time-dependent function calculated from the product of a quantity at a given time relative to an initial reference time. Specific autocorrelation functions are used to calculate vibrational spectra. For example, the velocity autocorrelation function is used to determine a power spectrum, and the dipole moment autocorrelation function is used to calculate the infrared spectrum.

A poorly defined material, possibly chromian illite or a mineral mixture.

The fabric of a soil or sediment ground mass where the fine material is described from the birefringence (“b-fabric”) based on the interference colors in thin section under crossed polarizers (after Bullock et al., 1985). Syn. clay birefringent fabric; see listing. Types of b-fabric relating to clay or other fine material include:

– cross striated b-fabric : Similar in description to reticulate striated b-fabric but with birefringent streaks showing non-perpendicular angular relationships in the ground mass.

– granostriated b-fabric : A b-fabric consisting of clay particles oriented parallel to skeletal grain surfaces.

– monostriated b-fabric : A fabric with birefringent streaks that are not associated with natural surfaces and occur isolated in the ground mass.

– mosaic-speckled b-fabric : A speckled b-fabric where a mosaic-like pattern occurs of coalescing birefringent regions or speckles.

– parallel striated b-fabric : A fabric with birefringent streaks that are not associated with natural surfaces and occur in parallel or sub- parallel sets in the ground mass.

– porostriated b-fabric : A striated b-fabric that consists of clay particles oriented parallel to the surface of pores.

– reticulate striated b-fabric : A ground mass with two sets of birefringent streaks intersecting at right angles. The streaks are not apparently associated with natural surfaces.

– speckled b-fabric : A ground mass (or pedoplasma or s-matrix) of predominantly clay where zones of birefringence show small (several microns), equidimensional, or slightly prolate regions or “speckles”.

– stipple-speckled b-fabric : A speckled b-fabric that consists of isolated regions or speckles.

– strial b-fabric : A ground mass composed mostly of clay characterized by preferred parallel birefringence orientation as an entity. This general orientation is commonly inherited from sedimentary processes and can occur in one or two preferred directions, “unistrial” and “bistrial”, respectively.

– striated b-fabric : A ground mass of predominantly clay with elongated birefringent zones or streaks showing nearly simultaneous extinction, commonly several hundred microns in size.

A poorly defined material, possibly muscovite and hematite.

See astrophyllite group.