Editing Biotite (section)

==Occurrence==

Members of the biotite group are found in a wide variety of [[igneous rock|igneous]] and [[metamorphic rocks]]. For instance, biotite occurs in the [[lava]] of [[Mount Vesuvius]] and in the Monzoni intrusive complex of the western [[Dolomites]]. Biotite in [[granite]] tends to be poorer in magnesium than the biotite found in its volcanic equivalent, [[rhyolite]].<ref name="CTV74">{{cite book |title=Igneous Petrology | publisher=McGraw-Hill |last1=Carmichael |first1=I.S. |last2=Turner |first2=F.J. |last3=Verhoogen |first3=J. |year=1974 |location=New York |pages=250 |isbn=978-0-07-009987-6}}</ref> Biotite is an essential [[phenocryst]] in some varieties of [[lamprophyre]]. Biotite is occasionally found in large cleavable crystals, especially in [[pegmatite]] veins, as in [[New England]], [[Virginia]] and [[North Carolina]] USA. Other notable occurrences include [[Bancroft, Ontario|Bancroft]] and [[Greater Sudbury|Sudbury]], [[Ontario]] Canada. It is an essential constituent of many metamorphic [[schist]]s, and it forms in suitable compositions over a wide range of [[pressure]] and [[temperature]]. It has been estimated that biotite comprises up to 7% of the exposed continental crust.<ref>{{cite journal|last1=Nesbitt|first1=H.W|last2=Young|first2=G.M|title=Prediction of some weathering trends of plutonic and volcanic rocks based on thermodynamic and kinetic considerations|journal=Geochimica et Cosmochimica Acta|date=July 1984|volume=48|issue=7|pages=1523–1534|doi=10.1016/0016-7037(84)90408-3 |bibcode=1984GeCoA..48.1523N}}</ref>

An igneous rock composed almost entirely of dark mica (biotite or phlogopite) is known as a ''[[glimmerite]]'' or ''biotitite''.<ref name="glimmerite">{{cite journal|title=Malawi glimmerites|doi=10.1016/0899-5362(88)90012-7|last=Morel|first=S. W.|journal=Journal of African Earth Sciences|volume=7|year=1988|pages=987–997|issue=7/8|bibcode=1988JAfES...7..987M}}</ref>

Biotite may be found in association with its common alteration product [[Chlorite group|chlorite]].<ref name="min-rock-sec"/>

The largest documented single crystals of biotite were approximately {{convert|7|m2|abbr=on}} sheets found in [[Iveland]], Norway.<ref>{{cite journal| url = http://www.minsocam.org/ammin/AM66/AM66_885.pdf| journal = American Mineralogist| volume = 66| pages = 885–907| year= 1981| title= The largest crystals| author = P. C. Rickwood}}</ref>

<gallery widths="180px" heights="120px" >
File:Biotite Granite student sample.jpg|Biotite-bearing granite samples (small black minerals).
File:Biotite Gneiss.JPG|Biotite-bearing gneiss sample.
File:Biotite and chlorite gneiss mg 7971.jpg|Gneiss sample bearing biotite and chlorite (green), a common alteration product of biotite.
File:Sheet mica, Namibia.jpg|Glimmerite from [[Namibia]].
</gallery>