A layered manganese oxide mineral (phyllomanganate) similar in structure to chalcophanite. The formula of a synthetic sample used in a structure determination (Post and Veblen, 1990) is Mg_0.29Mn⁴⁺_1.42Mn³⁺_0.58O₄ . 1.7H₂O, assuming no Mn vacancies and an analysis total of 100%. Chalcophanite has a sheet of edge sharing Mn-O octahedra where one in seven octahedra is vacant. Zn cations are located above and below the vacant sites, also in octahedral coordination, with oxygen atoms from the octahedral sheet and from a plane of H₂O molecules between the Mn-O sheets. Interlayer cations in birnessite, Mg, Na, K, Ca, etc., may occupy the Zn site and/or H₂O sites (as found in chalcophanite). However, distributions of the interlayer cation and H₂O sites in birnessite may also differ for various compositions (e.g., Na- vs Mg-rich birnessite), and the occupancy of the interlayer cation/H₂O sites is believed to produce observed superstructures. Cation exchange and redox reactions can occur in birnessite. Ranceite is the (interlayer cation) Ca end member of birnessite and takanelite has Mn²⁺ as the interlayer cation. “Buserite” is a hydrated form of birnessite with a 10-Å spacing instead of the 7-Å value of birnessite. “Buserite” has not been found in nature and is not a mineral, but is a common phase during synthesis of birnessite. Birnessite is a major Mn-rich phase in many soils, in desert varnish, in ocean manganese nodules, and as an alteration product in Mn-rich ore deposits. Australian soils containing birnessite may be related to neutral to slightly alkaline conditions, but this result is not universal and the presence of birnessite may instead be related to a paucity of Ca and Mg of these soils.

See bisque.

a) unglazed ceramic that has undergone firing;

b) the dried, but not yet fired, enamel coating. The bisque firing temperature is that initially used to stabilize the ceramic prior to glazing.
Syn., biscuit

A trioctahedral member of the brittle mica group. The end-member formula is: CaLiAl₂(BeAlSi₂)O₁₀(OH)₂. Compositional range restriction includes ^viLi > ^vi□, where □ = vacancy (i.e., ^viLi < ^vi□ is defined as margarite). Bityite forms in the 2M₁ polytype and has been found in pegmatites from Madagascar, Zimbabwe, and the Urals, and in a tin vein in Uganda. Like margarite, bityite (Lin and Guggenheim, 1983) has nearly complete tetrahedral ordering of Al,Be vs Si, and thus is non-centric in symmetry (Cc space group).
Cf., margarite

Bixbyite, alpha-(Mn³⁺,Fe³⁺)₂O₃, is structurally comprised of edge sharing and corner sharing (Mn,Fe)O₆ octahedra. Bixbyite has been reported from non-metamorphosed sediments where it had transformed from todorokite-birnessite, and from hydrothermal and low grade metamorphic deposits.

Used in decolorizing oil products, typically fuller’s earth or bentonite, by adsorption. For example, bleaching earth is used to remove the green color of chlorophyl in some cooking oils.
Syn., bleaching earth

See bleaching clay.

See blunging.

A processing term used in industry to describe the high-energy mixing or disaggregation of clay (or a similar substance) into water to form a uniform slurry (i.e., suspension or slip) for use in ceramics or paper making. A blunger usually consists of a round or octagonal tank with a mixer-impeller attrition blade. Post-blunging slurry processing may be performed to separate and concentrate the clay mineral phase or remove grit and heavy minerals, via wet sieve, hydrocyclone, flotation, gravity separation, chemical modification and/or magnetic separation.
See suspension, grit

Boehmite, or gamma-AlO(OH), is a hydrous aluminum oxide comprised of corrugated sheets of double edge-sharing octahedra of Al–O,OH. Boehmite is isostructural with lepidocrocite, the Fe analogue. Bauxite is a mixture of diaspore, gibbsite, and boehmite, and any one of the three may dominate.
Syn., böhmite