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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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References in periodicals archive ?
Finally, the lower stretch of the river runs over two-mica granite, followed by biotitic gneiss at the mouth, where the largest area of alluvial materials is also found [28] (Figure 1).
The Madrid Basin is bounded by three main mountain ranges: the Spanish Central System to the north (Somosierra mountains, composed of slates, phyllites and quartzites) and west (Guadarrama Sierra, mainly composed of granodiorites, biotitic granites, gneisses, pegmatites and schists), the Iberian Range to the east (mainly composed of limestones, dolostones, marls and arenites) and the igneous metamorphic series of the Toledo Mountains to the south (Aparicio-Yague and Garcia-Cacho, 1984; Calvo, 1989a; Villaseca et al., 1993; Sopena et al., 2004).
values are less than 9.98 A (biotitic illite has greater than 10.1 A values) when observed in glycolated samples (Petschick et al.
72 is biotitic granodiorite from a large rock wall of a cirque of the Gharesa glacier (5 500 m, Fig.