Boehmite or böhmite is an

aluminium oxide hydroxide Aluminium hydroxide oxide or aluminium oxyhydroxide, AlO(OH) is found as one of two well defined crystalline phases, which are also known as the minerals boehmite and diaspore. The minerals are important constituents of the aluminium ore, bauxite ...

(γ-AlO(OH)) mineral, a component of the

aluminium Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. I ...

ore

bauxite Bauxite is a sedimentary rock with a relatively high aluminium content. It is the world's main source of aluminium and gallium. Bauxite consists mostly of the aluminium minerals gibbsite (Al(OH)3), boehmite (γ-AlO(OH)) and diaspore (α-AlO ...

. It is dimorphous with diaspore. It crystallizes in the orthorhombic dipyramidal system and is typically massive in habit. It is white with tints of yellow, green, brown or red due to impurities. It has a vitreous to pearly luster, a

Mohs hardness The Mohs scale of mineral hardness () is a qualitative ordinal scale, from 1 to 10, characterizing scratch resistance of various minerals through the ability of harder material to scratch softer material. The scale was introduced in 1812 by t ...

of 3 to 3.5 and a

specific gravity Relative density, or specific gravity, is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for liquids is nearly always measured with respect to water at its densest ...

of 3.00 to 3.07. It is colorless in thin section, optically biaxial positive with

refractive indices In optics, the refractive index (or refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium. The refractive index determines how much the path of light is bent, or ...

of nα = 1.644 - 1.648, nβ = 1.654 - 1.657 and nγ = 1.661 - 1.668. Boehmite occurs in tropical laterites and bauxites developed on

alumino-silicate Aluminosilicate minerals ( IMA symbol: Als) are minerals composed of aluminium, silicon, and oxygen, plus countercations. They are a major component of kaolin and other clay minerals. Andalusite, kyanite, and sillimanite are naturally occurrin ...

bedrock. It also occurs as a

hydrothermal alteration Metasomatism (from the Greek μετά ''metá'' "change" and σῶμα ''sôma'' "body") is the chemical alteration of a rock by hydrothermal and other fluids. It is the replacement of one rock by another of different mineralogical and chemical co ...

product of corundum and

nepheline Nepheline, also called nephelite (), is a rock-forming mineral in the feldspathoid groupa silica-undersaturated aluminosilicate, Na3 K Al4 Si4 O16, that occurs in intrusive and volcanic rocks with low silica, and in their associated pegmatite ...

. It occurs with kaolinite,

gibbsite Gibbsite, Al(OH)3, is one of the mineral forms of aluminium hydroxide. It is often designated as γ-Al(OH)3 (but sometimes as α-Al(OH)3.). It is also sometimes called hydrargillite (or hydrargyllite). Gibbsite is an important ore of aluminiu ...

and diaspore in bauxite deposits; and with nepheline, gibbsite, diaspore,

natrolite Natrolite is a tectosilicate mineral species belonging to the zeolite group. It is a hydrated sodium and aluminium silicate with the formula . The type locality is Hohentwiel, Hegau, Germany. It was named natrolite by Martin Heinrich Klapro ...

and

analcime Analcime (; ) or analcite is a white, gray, or colorless tectosilicate mineral. Analcime consists of hydrated sodium aluminium silicate in cubic crystalline form. Its chemical formula is Na Al Si2 O6· H2O. Minor amounts of potassium and calci ...

in nepheline pegmatites. Industrially, it is used as an inexpensive

flame retardant The term flame retardants subsumes a diverse group of chemicals that are added to manufactured materials, such as plastics and textiles, and surface finishes and coatings. Flame retardants are activated by the presence of an ignition source and ...

additive for fire-safe polymers. It was first described by J. de Lapparent in 1927 for an occurrence in the bauxites of Mas Rouge,

Les Baux-de-Provence Les Baux-de-Provence (; oc, label=Provençal dialect, Provençal, Lei Bauç de Provença), commonly called Baux, is a Communes of France, commune in the Bouches-du-Rhône Departments of France, department in the Provence-Alpes-Côte d'Azur Regio ...

France France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of overseas regions and territories in the Americas and the Atlantic, Pacific and Indian Oceans. Its metropolitan area ...

, and named for the Bohemian-German chemist

Johann Böhm Johann Böhm (20 January 1895 – 27 November 1952) was a German Bohemian chemist who focused on photochemistry and radiography. The aluminum-containing mineral ''boehmite'' (or ''böhmite'') was named after him.

(1895–1952) who carried out X-ray studies of aluminium oxide hydroxides in 1925 (and not for the German geologist

Johannes Böhm Johannes Böhm (1857–1938) was a German geologist and palaeontologist. He was a researcher in the Prussian Geological Institute in Berlin Berlin ( , ) is the capital and largest city of Germany by both area and population. Its 3.7 milli ...

(1857–1938) as often stated).

References

Steven Dutch, 2002, Lepidocrocite and Boehmite Structure, University of Wisconsin - Green Bay
{{Authority control Hydroxide minerals Aluminium minerals Orthorhombic minerals Minerals in space group 63

See also

References