Absolute humidity

See humidity.

Absorption

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)

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).

Accessory mineral

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.

Achlusite

A poorly defined material, possibly sodium mica.

Acicular

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