As defined in the Bragg equation for diffraction, nλ = 2d Sinθ, where n is an integer, λ is the wavelength, θ is the glancing angle of incidence, and d is the (perpendicular) spacing between the diffracting planes. Because d is defined as a spacing, the term d spacing is redundant.
See Bragg equation

A trans-vacant phyllosilicate is dioctahedral with the vacancy ordered to the site where the OH,F anions are on opposite octahedral corners (i.e., trans orientation). Trans sites are located on the mirror plane of an ideal layer in a phyllosilicate.
Cf., cis-vacant

2:1:1 layer previously used to describe chlorite where a 2:1 layer plus an interlayer describes thesheet and layer configuration. This nomenclature is no longer in use, see Guggenheim et al. (2006) and references therein. Use 2:1 layer.
Cf., tetrahedral sheet, octahedral sheet, layer, interlayer material

2:2 layer previously used to describe chlorite where a 2:1 layer plus an interlayer was summed to two tetraheral sheets and two octahedral sheets. This nomenclature is no longer in use, see Guggenheim et al. (2006) and references therein. Use 2:1 layer.
Cf., tetrahedral sheet, octahedral sheet, layer, interlayer material

In clay science, absorption occurs where the sorbate enters internal layers, voids, or pore spaces within the sorbent (usually, clay material). Other scientific fields, often do not specify a mechanism.

absorption edge (X-ray) The -“edge” concept (as in an “absorption edge”) is often used wherever there is a sharp drop (or increase) in a characteristic of a graph. For example, graphs of X-ray absorption vs energy (or wavelength) show a sharp decrease in absorption for foils of specific metals at distinct X-ray wavelengths, and these wavelengths mark the metal’s absorption edges. Metal foils have been used to reduce or remove extraneous X-ray wavelengths in (early) X-ray experiments; more modern experiments use a monochromator crystal. Because these absorption edges are characteristic for the metal, they may be used to identify the local atomic structure of the metal in a phase in spectroscopic studies, such as XANES (X-ray Absorption Near-Edge Structure) or EXAFS (Extended X-ray Absorption Fine Structure).

A mineral present in a rock which is not essential for the classification of that rock. Characterizing accessory minerals are often used as modifiers to the rock name, for example, as in nepheline basalt.

A poorly defined material, possibly sodium mica.

A crystal habit composed of radiating masses of slender needle-like crystalline phases.

A clay (most often a Ca-bentonite) treated with concentrated acid in aqueous suspensions and, depending on how the clay is to be used, at various elevated temperatures and subsequently washed, dried, and pulverized. The modification results in enhancements in surface acidity, increased specific surface area, and higher porosity, all of which improve edible-oil bleaching or adsorption properties. Surface acidity for a clay was noted by K. Kobayashi in 1899 in Japan, and he termed the clay as “acid clay”. Hence, “acid clay” and “activated clay” are separately described in Japan. More recent adaptations of acid activation applied to other fuller’s earth clays (e.g., clays rich in sepiolite or palygorskite or mixture of palygorskite and montmorillonite) have either improved upon or eliminated processing steps associated with “classical” acid activation to produce different bleaching clay products for refining numerous edible oils. It is common to include the activation process when describing activated clays, e.g., “thermal-activated clay”, “Na₂CO₃-activated clay”.
See also bleaching clay, fuller’s earth;
Cf., activated clay, beneficiation, bleaching clay