The rock term for an aluminum ore consisting of primarily hydrous aluminum oxides [gibbsite, Al(OH)₃; boehmite, AlO(OH); and diaspore AlO(OH)], often mixed with iron oxyhydroxides (goethite, FeO(OH), and hematite, Fe₂O₃), kaolinite, and small amounts of anatase (TiO₂). Most bauxite deposits result from weathering of a variety of Al-rich source rocks that are low in comparatively stable silicates. Bauxite deposits are related to paleo-tropical or subtropical climate rather than lithology, especially where long periods of tectonic stability permitted “deep and thorough” weathering of the precursor rock.
Cf., bauxitic clay

Clay material containing minerals rich in their bulk aluminum content (e.g., gibbsite, boehmite, diaspore). This material is used for making refractories or as an ore for aluminum metal.
See bauxite

An obsolete term for oolitic chlorite, possibly chamosite.

A polymorph of Al(OH)₃ that occurs rarely in nature. The gibbsite Al(OH)₃ octahedral layer is similar to the dioctahedral layer in bayerite, but the stacking of the layers differs. Small distortions in the bayerite octahedra produce an overall two-layer structure. A notable occurrence for bayerite is in sedimentary rocks from Hartrurim, Israel, where bayerite is in association with calcite, gypsum, portlandite, and ettringite.
Cf., gibbsite, nordstrandite

BCF theory describes crystal growth as nucleation and further crystallization by way of layer-by-layer attachment at edge, step, or kink sites on the surface of the growing crystal, as a function of the saturation state of the parent solution. Nucleation can occur at surfaces, dislocations, or impurities. The kinetics are influenced by temperature, impurity concentration, etc.

A dioctahedral member of the smectite group. An important characteristic of this member is that isomorphous substitution occurs primarily in the tetrahedral sites to produce the net negative charge on the 2:1 layer (Güven, 1988). An idealized formula for beidellite is R⁺_0.33Al₂(Si_3.67Al_0.33)O₁₀(OH)₂.nH₂O, where R is an exchangeable cation, in this case univalent, but other valences are possible. The iron (Fe³⁺) analogue is known as nontronite and intermediate compositions are known. Beidellite is found abundantly as weathering products of volcanic ash, in association with hydrothermal environments, and as diagenetic products. An especially pure end-member beidellite comes from the Black Jack Mine, Idaho, USA.
Cf., smectite.

As described by Schultz (1969) based on chemical and thermal analysis, beidellite-type montmorillonite is a type of montmorillonite characterized by a large net negative layer charge of -0.85 to -1.20 per O20(OH)4, with tetrahedral substitutions causing more than 50% of the total layer. Current (chemical) nomenclature for montmorillonite is that it is an Al-rich, dioctahedral smectite with an ideal structural formula of (Al3.15.Mg0.85)Si8O20(OH)4X0.85.nHO with layer charge from primarily octahedral substitutions of Mg, whereas beidellite has a net layer charge that occurs from tetrahedral substitutions of Al, with an ideal structural formula of Al4.0(Si7.15Al0.85)O20(OH)4X0.85.nH2O. The term ”beidellite-type montmroillonite” is obsolete and should not be used.

A modulated 1:1 layer silicate with octahedral sheets interlayered by a continuous tetrahedral sheet with double 6-fold tetrahedral rings (Heinrich et al., 1994). The 6-fold rings are interconnected and have tetrahedra pointing up and down, and adjacent octahedral sheets are connected with 5- and 7-fold tetrahedral rings. The ideal chemical composition is M₇Si₆O₁₅(OH)₈, where M are medium size cations, such as Mn, Fe, Mg, Zn. Small amounts of Al are known to enter the tetrahedral site for Si. Important localities include Franklin, New Jersey, USA in a metamorphosed, zinc stratiform ore body, and the Olympic peninsula, Washington, USA.
Cf., armbrusterite, parsettensite, pyrosmalite, innsbruckite, varennesite

a) a process or processes to concentrate an ore mineral. The British equivalent is “mineral dressing”.

b) the process of improving the performance characteristics of an industrial clay by processing and/or the addition of chemical additives, e.g., bentonite.

a) Mineralogical/Petrological term: A soft, plastic, light-colored rock composed primarily of clay minerals of the smectite group, particularly the clay mineral montmorillonite, which typically forms from chemical alteration of glassy volcanic ash or tuff under marine or hydrothermal conditions. Bentonite may contain accessory crystal grains that were originally phenocrysts in the parent rock as well as secondary authigenic mineral phases such as K- rich feldspar. Diagenetic or low-grade metamorphic alteration can modify the smectite to a variety of interstratified illite-smectite minerals, resulting in materials known as K-bentonites.

b) Industrial term: A highly colloidal and plastic clay material, primarily composed of the clay mineral montmorillonite, that is commonly used in drilling mud, as a foundry sand binder, in cat litter, animal feed, cements, ceramics and various other industrial activities and products. Sodium bentonite swells significantly when exposed to water (to ~12X) whereas calcium bentonite has minimal swelling capability (to ~3X).
Cf., tonstein