See pyrosmalite.

An obsolete term for chromian muscovite.

In X-ray diffraction studies, full width at half maximum (FWHM) is a mathematical expression that describes the width (the independent variable, or the difference in two-theta values and thus “broadness”) of a reflection with a local maximum value (dependent variable, or the X-ray intensity and thus the “peak”). The FWHM value is calculated by subtracting the lower two-theta value from the higher two-theta value, which are at the position of half the maximum intensity value (a local reflection maximum). The FWHM value is often used in clay science to describe the reflection width in X-ray diffraction patterns for clay minerals. Other techniques, such as spectroscopic methods also use this expression, although with other independent and dependent variables (e.g., X-ray photon energy). The advantage of the FWHM expression (vs using the local maximum as the reflection location) is that reflection maxima are not always representative of the true reflection position, and the FWHM eliminates (or minimizes) the determination of errors in reflection position.
Cf., X-ray diffraction

A clay or other earthy material of fine particle size that is highly absorbent and/or is a natural bleaching earth. The term is derived from the historical use of certain clays to “full” or remove oils and other contaminants from raw woolen cloth.

Fulvic acids occur as a result of the decay of plants and microorganisms in some soils, sediments, peats, coals, shales, and surface waters. Unlike humic acids, fulvic acids are soluble in water over a large range of pH values (and this is the operational distinction between humic vs fulvic acids). Along with humic acid, fulvic acid may be extracted from solids using a strong base, such as NaOH or KOH. Fulvic acid may actually originate from hydrolysis of large molecules by the strong base during extraction. However, at pH 1, fulvic acid remains in solution but humic acid will precipitate.
Cf., humic acid, humification, humic substances, humin

A sequence of 2:1 dioctahedral or trioctahedral layers which are coherently related by rotations of multiples of 60^o. Such particles, as observed in sample separates, are assumed to be identical to the individual growth units in unseparated samples. Some data have shown that coherent scattering domains undergo separation during sample disaggregation, and that particles that result are not fundamental, but many investigators assume that there is a one-to-one relation between fundamental particles in separates and coherent scattering domains in unseparated soil or rock samples.
Cf., MacEwan crystallite, interparticle diffraction, coherent scattering domain

The unification of two or more particles such that the substances between the two particles is of the same material as the particles. Fusion often refers to the melting together of two substances. In clay science, aggregates may form without fusion with bridges forming between particles by H₂O or by polymers, such that they behave as an apparently larger particle.
Cf., flocculation

An obsolete term for chromian muscovite.

An obsolete term for a halloysite from Angleur, Belgium.

In mining, the non-economic host rock in which valuable minerals (usually metalliferous ore minerals) are found. When the gangue is discarded, this material is referred to as “tailings”.