An interlamellar arrangement of one layer of alkylammonium cations with the C-C-C plane of the alkyl chains (n < 8) parallel to the (001) plane of the 2:1 layer to produce a characteristic 13.6-Å spacing of a phyllosilicate. The positively-charged end groups (e.g., NH3+) of the alkylammonium cations are attached to alternate siloxane surfaces in the interlayer. See Lagaly and Weiss (1975); Lagaly (1994).
Cf., alkylammonium layer charge method, organoclay
An interlamellar arrangement of alkylammonium cations with the positively-charged (polar) end groups (e.g., NH3+) of the alkylammonium cations attached to the interlayer silicate surfaces of a 2:1 phyllosilicate. The alkyl chains are tilted from a perpendicular orientation with respect to the (001) surfaces, and this orientation produces basal spacings of>22Å. The angles between the alkyl chain axes and silicate 2:1 layers increase with layer charge and range from 50 to 60° in vermiculites and to 90° in micas. See Lagaly and Weiss (1969; 1975); Lagaly (1994).
Cf., alkylammonium layer charge method, alkylammonium organoclay bilayer, alkylammonium organoclay monolayer, alkylammonium organoclay pseudotrilayer, organoclay
An interlamellar arrangement of alkylammonium cations with the positively-charged (polar) end groups (e.g., NH3+) of the alkylammonium cations attached to the interlayer silicate surfaces of a 2:1 phyllosilicate. Kinks in the alkyl chains shift the (non-polar) alkyl group tails between other alkylammonium alkyl chains to form a pseudotrilayer with a characteristic spacing of ~22Å as determined from the thickness of three alkyl chains (Lagaly and Weiss, 1975; Lagaly, 1994).
Cf., alkylammonium layer charge method, alkylammonium organoclay bilayer, alkylammonium organoclay monolayer, organoclay
Obsolete name replaced by rectorite.
See rectorite
An “alligator hide/skin” texture relates to a macro-texture observed on exposed and weathered clay surfaces. The texture evolves from polygonal shrinkage cracks that develops from bentonites with low dialatancy.
See also popcorn texture.
A semiordered hydrous aluminosilicate, Al2O3(SiO2)1.3-2.0 2.5-3.0(H2O), that is closely related to imogolite because both seem to be incipient 1:1 minerals structurally and chemically, although it has been suggested that allophane may be an incipient montmorillonite. The ratio of SiO2 to Al2O3 is usually 1.3 to 2.0 for allophane, but has been reported as low as 0.83, a greater variation than in imogolite. Allophane shows curved walls with a more spherical morphology (30 – 50 Å spherical diameters) than imogolite, which is tube-like. Allophane is common in soilsderived from volcanic ash, but may be present in soils derived from basic igneous rocks in tropical climates or in podzol soils derived from more acidic rocks. Allophane may precipitate in hot springs rich in silicic acid and aluminum. Allophane is white or colorless when moist, but earthy when dried.
Syn., disordered allophane
Cf., imogolite
See suspension.
An alteromorph is an alteration product of a crystal that preserves the external anhedral form of the precursor mineral. The alteromorph may have a different chemical composition and/or crystal structure than the precursor crystal. The alteromorph can result from replacement in the solid state or by fluid interactions.
Cf., centripetal replacement, pseudomorph