Biotite

Biotite

Biotite is a common phyllosilicate mineral within the mica group, with the approximate chemical formula K(Mg, Fe)3AlSi3O10(F, OH)2. More generally, it refers to the dark mica series, primarily a solid-solution series between the iron-endmember annite, and the magnesium-endmember phlogopite; more aluminous endmembers include siderophyllite.

Biotite is a sheet silicate. Iron, magnesium, aluminium, silicon, oxygen, and hydrogen form sheets that are weakly bond together by potassium ions. It is sometimes called "iron mica" because it is more iron-rich than phlogopite. It is also sometimes called "black mica" as opposed to "white mica" (muscovite) -- both form in some rocks, in some instances side-by-side.

Like other mica minerals, biotite has a highly perfect basal cleavage, and consists of flexible sheets, or lamellae, which easily flake off. It has a monoclinic crystal system, with tabular to prismatic crystals with an obvious pinacoid termination. It has four prism faces and two pinacoid faces to form a pseudohexagonal crystal. Although not easily seen because of the cleavage and sheets, fracture is uneven. It has a hardness of 2.5–3, a specific gravity of 2.7–3.1, and an average density of 3.09 g/cm³. It appears greenish to brown or black, and even yellow when weathered. It can be transparent to opaque, has a vitreous to pearly lustre, and a grey-white streak. In its weathered yellow, sparkly form, it is a common type of “fool’s Gold” (Pyrite is the official “fool’s Gold”). When biotite is found in large chunks, they are called “books” because it resembles a book with pages of many sheets.

Biotite is found in a wide variety of igneous rocks and metamorphic rocks. For instance, biotite occurs in the lava of Mount Vesuvius and at Monzoni. It is an essential phenocryst in some varieties of lamprophyre. Biotite is occasionally found in large sheets, especially in pegmatite veins, as in New England, Virginia and North Carolina. Other notable occurrences include Bancroft and Sudbury, Ontario. It is an essential constituent of many metamorphic schists, and it forms in suitable compositions over a wide range of pressure and temperature.

It is not industrially useful, but it is mined using quarrying and underground mining (depending on the depth of the biotite) for collection purposes.

Biotite is used extensively to constrain ages of rocks, by either potassium-argon dating or argon-argon dating. Because argon escapes readily from the biotite crystal structure at high temperatures, these methods may provide only minimum ages for many rocks. Biotite is also useful in assessing temperature histories of metamorphic rocks, because the partitioning of iron and magnesium between biotite and garnet is sensitive to temperature.

Biotite is used in electrical devices, usually as a dielectric in capacitors and thermionic valves

Biotite was named by J.F.L. Hausmann in 1847 in honour of the French physicist Jean-Baptiste Biot, who, in 1816, researched the optical properties of mica, discovering many unique properties.

See also

*List of minerals
*picturs of Mica Biotite [http://groups.google.com.pk/group/micaexporters?hl=en&lnk=srg]

References

"The Mineral Biotite". 1995,1996 Amethyst Gallery Inc. [http://www.galleries.com/minerals/silicate/biotite/biotite.htm]

"Biotite Mineral Data". [http://webmineral.com/data/Biotite.shtml]

"Biotite". [http://library.thinkquest.org/05aug/00461/biotite.htm]

"BIOTITE". "LoveToKnow 1911 Online Encyclopedia". 2003, 2004 LoveToKnow. [http://33.1911encyclopedia.org/B/BI/BIOTITE.htm]


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  • Biotite — Catégorie IX : silicates[1] Biotite Monte Somma Italie (XX 5 mm) …   Wikipédia en Français

  • biotite — [ bjɔtit ] n. f. • 1848; de J. B. Biot, n. pr. ♦ Minéral. Variété de mica noir, utilisée comme matériau d isolation. ● biotite nom féminin (de J. B. Biot, nom propre) Mica monoclinique se présentant en lamelles hexagonales, de couleur noire et… …   Encyclopédie Universelle

  • Biotite — Bi o*tite, n. [From Biot, a French naturalist.] (Min.) Mica containing iron and magnesia, generally of a black or dark green color; a common constituent of crystalline rocks. See {Mica}. [1913 Webster] …   The Collaborative International Dictionary of English

  • biotite — [bī′ə tīt΄] n. [Ger biotit: so named after J. B. Biot (1774 1862), Fr physicist + it, ITE1] a dark colored, soft, monoclinic mica, K(Mg,Fe) 3 (Al,Fe)Si3O10 (OH) 2, found in igneous, metamorphic, and sedimentary rocks …   English World dictionary

  • biotite — Mica Mi ca, n. [L. mica crumb, grain, particle; cf. F. mica.] (Min.) The name of a group of minerals characterized by highly perfect cleavage, so that they readily separate into very thin leaves, more or less elastic. They differ widely in… …   The Collaborative International Dictionary of English

  • biotite — Mica Mi ca, n. [L. mica crumb, grain, particle; cf. F. mica.] (Min.) The name of a group of minerals characterized by highly perfect cleavage, so that they readily separate into very thin leaves, more or less elastic. They differ widely in… …   The Collaborative International Dictionary of English

  • biotite — biotitic /buy euh tit ik/, adj. /buy euh tuyt /, n. a very common mineral of the mica group, occurring in black, dark brown, or dark green sheets and flakes: an important constituent of igneous and metamorphic rocks. [1860 65; named after J. B.… …   Universalium

  • biotite — biotitas statusas T sritis chemija apibrėžtis Mineralas. formulė K(Mg,Fe,Mn)₃[(OH,F)₂|(Al,Fe)Si₃O₁₀] atitikmenys: angl. biotite rus. биотит …   Chemijos terminų aiškinamasis žodynas

  • biotite — noun Etymology: German Biotit, from Jean B. Biot died 1862 French mathematician Date: 1862 a generally black or dark green form of mica that is a constituent of crystalline rocks and consists of a silicate of iron, magnesium, potassium, and… …   New Collegiate Dictionary

  • biotite — noun /ˈbaɪəˌtaɪt/ A dark brown mica; it is a mixed aluminosilicate and fluoride of potassium, magnesium and iron …   Wiktionary


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