See Stern layer.

An invalid term, previously used as a classification of the micas where the number of silicon atoms per formula unit is three per four tetrahedral sites.
See Rieder et al. (1998).
Cf., mica, true mica, brittle mica, interlayer-deficient mica, group names.

A group name for platy phyllosilicates of 2:1 layer and a layer charge of ~ -1.0 per formula unit. True micas do not show swelling capacity. Rieder et al. (1998) defines the true micas as having greater than 50% of the interlayer cations as univalent cations. The true mica group is further divided into subgroups based on the octahedral sheet being either trioctahedral or dioctahedral.
Cf., mica, brittle mica, interlayer-deficient mica, group names

See reyerite group.

See Transition State Theory.

A member of the palygorskite-sepiolite group with a composition of approximately Na_1.87Fe_2.14Mn_0.48Ti_0.14 (Si₈O₂₀) (OH)₂^.n(H₂O).
See palygorskite-sepiolite group

In phyllosilicates, turbostratic stacking involves highly disordered (non regular) stacking arrangements of layers where there is no registry from one layer to another, much like a stack of playing cards lying flat on each other but with no alignment of edges. Smectite minerals and halloysite commonly have turbostratic stacking.
See rotational stacking disorder

See microfabric, clay.

The Udden-Wentworth scale (often referred to as the Wentworth scale) is a size scale (diameter) for clasts and is used primarily in sedimentology and related disciplines. The Udden-Wentworth scale considers size only and does not imply composition. The “clay” term in the scale has the potential to be confusing because “clay” is defined in clay mineralogy as having specific properties unrelated to particle size alone. Thus, to avoid confusion, use of “clay size” instead of “clay” is recommended here to delineate size characteristics of particles only. Further divisions, such as “fine”, “medium”, “coarse”, etc. may be used also. Pettijohn (1957) discusses the history of the use of size terms, alternative classification schemes, and modifications to the nomenclature.
See clay

A fine-particle sedimentary seat rock composed mainly of clay minerals, that is generally non-bedded and contains traces of plant roots. Kaolinite-rich underclay deposits are economically important for ceramics manufacturing. (modified from Huddle and Patterson, 1961)
Cf., seat rock, ball clay, flint clay, fire clay