An obsolete term for lepidolite.

An International System (SI) unit of measure equal to 10^-6 meters.

An old name for micrometer.

A general term for dietary essential nutrients required in relatively small amounts (less than 50 milligrams per day). For example, micronutrients include vitamins (organic compounds) and trace elements (e.g., Fe, Cu, Zn, I, Se, Mn, Mo, Cr, F, Co) for human consumption that may be potentially provided by ingestion of clays, whereas clays in soils provide these nutrients for plants.
Cf., macronutrient

In clay science, micropores (Figure 3) are cavities with diameters of <2 nm within a sample, following the IUPAC convention (Rouquerol et al., 1996), which is also similar in size to a common (upper) clay particle size used in clay studies. Thus, these pores are probably present at the edges of single stacks of unit structures and at widened edges of the interlayer. In soil science, micropores are defined as 5 - 30 μm, ultramicropores are 0.1 – 5 μm, and cryptopores are <0.1 μm (Soil Science Society of America, 1997). The pore volume distribution of clays is commonly determined by gas adsorption methods (typically H₂O, N₂ or, CO₂).
Cf., macropore, mesopore

In clay science and materials science, microstrain is a local strain caused by a local deviation of the lattice parameters from the mean value. Microstrain originates by 1) atomic substitutions where the ionic radius of the substituting ion differs from the original ion, 2) missing atoms or ions in the structure, 3) interactions with neighboring crystallites having slightly different lattice parameters, e.g., owing to twinning, an inhomogeneous mixture of crystallites with similar lattice parameters. In X-ray diffraction patterns, microstrain causes peak broadening. A microstrain expression is defined as the root-mean-square of the lattice parameters. In physics, mechanics, and many engineering disciplines, microstrain is a strain expressed in terms of parts per million (10^-6), where strain is defined as a ratio of the change in the distance/dimension to the original distance/dimension, and hence it has no unit and is dimensionless.

An obsolete term for a Cr-bearing kaolinite.

See reyerite group.

An element or chemical compound that is normally crystalline and that has been formed as a result of geological processes (quot Nickel, 1995). A mineral forms by a naturally occurring process (e.g., “geological” process); phases formed by the interaction of individuals (even if outdoors under conditions not fully controlled by the individual) are not minerals. Nickel (1995) discussed exceptions to the requirements, such as the equivalence of extraterrestrial and “geological” processes, metamict (non-crystalline) minerals, mercury (a liquid mineral), and others (quot Guggenheim et al., 2006). Some naturally occurring processes, but without a geological component, such as compounds that form biologically (e.g., oxalate crystals in certain plants, marine animal shells), are not minerals. Synthesized materials are not minerals, but may be referred to as “synthetic minerals” (e.g., “synthetic diamond”, “synthetic halite”) because the use of “synthetic” negates the naturally occurring/geological aspects specifically. Likewise, “biomineral” is acceptable for similar reasons as synthetic mineral.
See crystalline,
Cf., biologically controlled mineralization, biologically induced mineralization, biomineralization

A natural solid with insufficient long-range atomic ordering to be classified as a mineral. For example, limonite (FeO . OH . nH₂O) is often considered an amorphous “mineral” or mineraloid.