An obsolete term for illite.

An obsolete term for poorly described Ni- and Mg-rich phyllosilicates, generally characterized as “garnierite”.

The Mn-analogue of cronstedtite, a serpentine. Guidottiite has an ideal composition of (Mn₂Fe³⁺)(SiFe³⁺)O₅(OH)₄. Guidottiite-2H₁ and -2H₂ were reported by Wahle et al. (2010) with random interstratified polytype intergrowths and stacking disorder common. The sample comes from the Kalahari Manganese field, South Africa, and forms from hydrothermal solutions.

An obsolete term for illite-2M₂.

See “deweylite”.

See reyerite group.

Habit refers to the general shape of mineral particles, as in the “platy” habit of clay particles, inclusive of shapes that reflect the internal arrangement of atoms as well as crystal growth features. Examples of habits include acicular, lamellar, and equant.

The time, t_1/2, required for the number of radioactive atoms in a system to decay and thus decrease to half of the original number.

A poorly defined material, possibly paragonite and lithian muscovite.

An obsolete name for altered material, probably vermiculite.