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biotite

biotite An important rock-forming silicate mineral; a member of the mica group K2(Mg,Fe)6[Si3AlO10]2(OH,F)4, in which the Mg/Fe ratio is less than 2:1; biotite forms a series with phlogopite (of similar composition, but with Mg/Fe greater than 2:1) and may have Fe3+, Ti4+, and Al3+ also present in the formula; sp. gr. 2.7–3.3; hardness 2–3; monoclinic; black, dark brown, or greenish-black; vitreous to sub-metallic lustre; crystals tabular and pseudo-hexagonal, with lamellar aggregates and flakes; cleavage perfect basal mica; occurs in granites, syenites, and diorites, in schists and gneisses, in contact metamorphic rocks, and often in sedimentary rocks.

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"biotite." A Dictionary of Earth Sciences. . Encyclopedia.com. 27 Apr. 2017 <http://www.encyclopedia.com>.

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"biotite." A Dictionary of Earth Sciences. . Retrieved April 27, 2017 from Encyclopedia.com: http://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/biotite

biotite

biotite (bī´ətīt´), iron-rich variety of phlogopite, most abdunant of the mica minerals.

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"biotite." The Columbia Encyclopedia, 6th ed.. . Encyclopedia.com. 27 Apr. 2017 <http://www.encyclopedia.com>.

"biotite." The Columbia Encyclopedia, 6th ed.. . Encyclopedia.com. (April 27, 2017). http://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/biotite

"biotite." The Columbia Encyclopedia, 6th ed.. . Retrieved April 27, 2017 from Encyclopedia.com: http://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/biotite