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A dark-brown or dark-green to black mica, K(Mg,Fe)3(Al,Fe)Si3O10(OH)2, found in igneous and metamorphic rocks.

[After Jean Baptiste Biot (1774-1862), French physicist.]

bi′o·tit′ic (-tĭt′ĭk) adj.
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Adj.1.biotitic - relating to or involving biotite
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hirsuta is not a cave in the true sense, but comprises an outcrop of granitic and biotitic feldsparic gneiss that split vertically, forming a narrow rock fissure that transects the outcrop from north to south and from top to bottom (Fig.
Ngouaka Lode Au Discovery, South Gold Belt: The gold mineralization at Ngouaka includes disseminated auriferous pyrite and quartz-pyrite veins in altered and silicified, quartz-veined biotitic quartzites and amphibolites.
All of the remaining samples were comprised of variations of the bulk host lithology of garnetiferrous, biotitic gneiss.