Biotite metamorphism

Table 5.44 Compositions (in weight %) of some natural amphiboles (from Deer et al., 1983) (1) = anthophyllite from a serpentinite (2) gedrite from a gedrite-kyanite-garnet paragenesis (3) cummingtonite from a oligoclase-biotite schist (4) common hornblende from a tonalite (5) pargasite from a metamorphic limestone (6) basaltic hornblende from a lathe (7) glaucophane from a glaucophane schist. ...

In thermal metamorphism, biotite occurs in the clorite-sericite facies as a dispersed phase in the argillitic matrix and is stable up to low-grade cornubianites. In regional metamorphism, biotite is typical of argillitic and pelitic rocks up to the staurolite-garnet facies (biotite, biotite-sericite, biotite-chlorite, and albite-biotite schists, and garnet-staurolite micaschists). 

Biotite Gabbros, norites, diorites, granites, pegmatites Phyllites, chlorite-sericite schists, biotite facies of the regional metamorphism, gneisses ... 

Table 5.55 Chemical analyses of natural micas (from Deer et al., 1983). Note that ionic fractions are retrieved on a 24-anion basis—i.e. double the canonical formula. (1) Muscovite from a low-grade metamorphic prasinite schist (2) glauconite from a sandstone (3) phlogopite from a marble (4) biotite from a quartz-bearing latite (5) lepidolite from a pegmatite. ...

Microlithofacial classification of the sandstones is based on Dott s classification modified by Pettijohn et al. (1972). They are mostly arenites and subarkose and quartz wackes (rare sublithic, sporadically lithic and arkosic). Quartz is the main component of the sandstones (about 60-70 vol. percent). Feldspars (6 vol. percent) are mostly represented by potassium feldspars with plagioclases in lesser amounts. Some micas (muscovite and biotite) and chlorites are observed. Mica content of arenites reaches 3 vol. %, but is higher in the wackes. Heavy minerals present include zircon, sphene, rutile and apatite. Magmatic rocks (volcanic more than Plutonic) are predominant among lithoclasts (about 2 vol. %), but some metamorphic and sedimentary clasts being present too. 

Fig. 3.52 Plot of of quartz vs magnetite solid squares) and of biotite vs muscovite (open squares) from rocks whose peak metamorphic conditions range from greenschist through granulite facies (after Kohn, 1999)...

Ganguly J., Chakraborty S., Sharp T.G., and Rumble D. (1996) Constraint on the time scale of biotite-grade metamorphism during Acadian orogeny from a natural garnet-garnet diffusion couple. Am. Mineral. 81, 1208-1216. 

Typically illite-rich sediments develop the assemblage chlorite-illite-quartz or chlorite-illite-biotite-quartz upon epi-metamorphism (Maxwell and Hower, 1967 Dunoyer de Segonzac, 1969). 

AMPHIBOLITE. The amphibolites form a large group of rather important rocks of metamorphic character. As the name implies they are made up very largely of minerals of the amphibole group. There may be also a variety of other minerals present, such as quartz, feldspar, biotite, muscovite, garnet, or chlorite in greater or lesser amounts. 

Biotite is occasionally found in large sheets, especially in pegmatite veins. It also occurs as a contact metamorphic mineral or the product of the alteration of hornblende, augite, wernerite, and similar minerals. 

Alicudi rocks, like other Aeolian volcanics, contain a variety of meta-morphic and magmatic xenoliths. Metamorphic xenoliths are represented by predominant quartz-rich rocks displaying evidence of partial melting along grain boundaries, and by a few biotite gneiss and granulite... 

Wescott, M. R. (1966) Loss of argon from biotite in a thermal metamorphism. Nature, 210, 83-4. 

Numerous structure refinements of biotites reviewed elsewhere (Bailey, 1984), together with Mossbauer spectral measurements of suites of specimens from igneous and metamorphic rocks (Bancroft and Brown, 1975 Dyar and Bums, 1986 Dyar, 1987), have revealed that Fe2+ ions are slightly enriched in the cis-M2 sites which are marginally smaller in size than the centrosymmetric trans-M1 sites. In metamorphic biotites, the Fe2+ ions are more highly enriched in the ris-M2 sites than in biotites from igneous rocks. 

Metamorphic Marble/skam, biotite schist Monazite, columbite and Parts of Tirunelvelli-Tiruchinapalli,... 

On an AFM diagram (Fig. 16) all the minerals from iron-formations proper fall into a narrow and clearly defined field, while the rock-forming minerals of the associated iron-rich shales from BIF of Superior type (chamosite, ripidolite and other chlorites, garnets and some biotites) form another broader and less clear-cut field. These two fields do not overlap, which indicates the isochemical character of metamorphism and the limited mobility of the main rock-forming minerals, at least within individual layers and bands of the iron-formations and shales. The chemical composition of stilpnomelane occupies an intermediate position both in iron content and in alumina content. However, a high content of potassium (up to 2.2% K2O), an element not typical of most BIF, is necessary for the formation of this mica. 

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