BIOTITE  , an important See also:

• ROCK
• ROCK (O.Fr. rake, Sp. rota, Ital. rocca; possibly from a Lat. form rupica, from rupes, rock)
• ROCK, DANIEL (1799–187t)

rock-forming See also:

• MINERAL

mineral belonging to the See also:

• GROUP

group of micas (q.v.) . The name was given by J . F . L . See also:

• HAUSMANN, JOHANN FRIEDRICH LUDWIG (1782-1859)

Hausmann in 1847 in See also:

• HONOUR (Lat. honos or lwnor, honoris; in English the word was spelled with or without the u indifferently until the 17th century, but during the 18th century it became fashion-able to spell the word " honor "; Johnson's and Webster's Dictionaries stereoty

honour of the See also:

• FRENCH
• FRENCH, DANIEL CHESTER (1850– )
• FRENCH, NICHOLAS (1604-1678)

French physicist, J . B . See also:

• BIOT, JEAN BAPTISTE (1774-1862)

Biot, who in 1816 found the See also:

• MAGNESIA

magnesia-micas to be optically uniaxial or nearly so . The magnesia-micas are now referred to the See also:

• SPECIES

species biotite and See also:

• PHLOGOPITE

phlogopite, which differ in that the former contains a considerable but widely varying amount of hon . Biotite is an orthosilicate of See also:

• ALUMINIUM (symbol Al; atomic weight 27.0)

aluminium, See also:

• MAGNESIUM [symbol Mg, atomic weight 24.32 (0 = 16)]

magnesium, ferrous and ferric See also:

• IRON [symbol Fe, atomic weight 55.85 (0=16)]

iron, See also:

• POTASSIUM [symbol K (from kalium), atomic weight 39.114 0=16)]

potassium and basic See also:

• HYDROGEN [symbol H, atomic weight x-oo8 (0=16)]

hydrogen, with small amounts of See also:

• CALCIUM [symbol Ca, atomic weight 40.0 (o= x6)]

calcium, See also:

• SODIUM [symbol Na, from Lat. natrium; atomic weight 23.00 (0=16)]

sodium, See also:

• LITHIUM [symbol Li, atomic weight 7•oo (0=16)]

lithium, See also:

• FLUORINE (symbol F, atomic weight 19)

fluorine, See also:

• TITANIUM [symbol Ti, atomic weight 48.1 (0 = 16)]

titanium, &c., and ranges in See also:

• COMPOSITION
• COMPOSITION (Lat. compositio, from componere, to put together)

composition between (H,K)z(Mg,Fe)4(Al,Fe)z(SiO4)4 and (H,K) z(Mg,Fe) zAlz(SiO4) 3 . Like the other micas, it is See also:

• MONOCLINIC

monoclinic with pseudo-hexagonal symmetry (See also:

• FIGS

figs . 1, 2) and possesses a perfect cleavage in one direction (c) . Biotite is, however, readily distinguished by its darker See also:

• COLOUR (Lat. color, connected with celare, to hide, the root meaning, therefore, being that of a covering)

colour, strong pleochroism, and small optic axial See also:

• ANGLE (from the Lat. angulus, a corner, a diminutive, of which the primitive form, angus, does not occur in Latin; cognate are the Lat. angere, to compress into a bend or to strangle, and the Gr. ayKOS, a bend; both connected with the Aryan root ank-, to

angle .

The colour is usually dark-See also:

• GREEN, A
• GREEN, ALEXANDER HENRY (1832—1896)
• GREEN, DUFF (1791—1875)
• GREEN, JOHN RICHARD (1837—1883)
• GREEN, MATTHEW (1696-1737)
• GREEN, THOMAS HILL (1836-1882)
• GREEN, VALENTINE (1739–1813)
• GREEN, WILLIAM HENRY (.1825–1900)

green or See also:

• BROWN
• BROWN, CHARLES BROCKDEN (1771-181o)
• BROWN, FORD MADOX (1821-1893)
• BROWN, FRANCIS (1849- )
• BROWN, GEORGE (1818-188o)
• BROWN, HENRY KIRKE (1814-1886)
• BROWN, JACOB (1775–1828)
• BROWN, JOHN (1715–1766)
• BROWN, JOHN (1722-1787)
• BROWN, JOHN (1735–1788)
• BROWN, JOHN (1784–1858)
• BROWN, JOHN (1800-1859)
• BROWN, JOHN (1810—1882)
• BROWN, JOHN GEORGE (1831— )
• BROWN, ROBERT (1773-1858)
• BROWN, SAMUEL MORISON (1817—1856)
• BROWN, SIR GEORGE (1790-1865)
• BROWN, SIR JOHN (1816-1896)
• BROWN, SIR WILLIAM, BART
• BROWN, THOMAS (1663-1704)
• BROWN, THOMAS (1778-1820)
• BROWN, THOMAS EDWARD (1830-1897)
• BROWN, WILLIAM LAURENCE (1755–1830)

brown; thick crystals are often deep-See also:

• BLACK
• BLACK, ADAM (1784-1874)
• BLACK, JEREMIAH SULLIVAN (1810–1883)
• BLACK, WILLIAM (1841-1898)

black and opaque . The absorption of See also:

• LIGHT

light-rays vibrating parallel to the cleavage is much greater than of rays vibrating in a direction perpendicular thereto, and in dark-coloured crystals the former are almost completely absorbed . The angle between the optic axes is usually very small, the crystals being often practically uniaxial; an axial angle of 500 has, however, been recorded in a dark-coloured biotite . The specific gravity of biotite is, as a See also:

• RULE

rule, higher than that of other micas, varying from 2.7 to 3•1 according to the amount of iron See also:

• PRESENT

present . The hardness is 22 to 3 . Several varieties of biotite are distinguished . By G . Tschermak it is divided into two classes, meroxene and anomite; in the former the See also:

• PLANE

plane of the optic See also:

• AXIS (Lat. for " axle ")

axis coincides with the plane of symmetry, whilst in the latter it is perpendicular thereto . Meroxene includes nearly all See also:

• ORDINARY (med. Lat. ordinarius, Fr. ordinaire)

ordinary biotite, and is the name given by A . Breithaupt in 1841 to the Vesuvian crystals; on the other See also:

• HAND
• HAND (a word common to Teutonic languages; cf. Ger. Hand, Goth. handus)
• HAND, FERDINAND GOTTHELF (1786-185r)

hand, anomite (named from bop-or, "contrary to See also:

• LAW
• LAW (0. Eng. lagu, M. Eng. lawe; from an old Teutonic root lag, " lie," what lies fixed or evenly; cf. Lat. lex, Fr. loi)
• LAW, JOHN (1671—1729)
• LAW, WILLIAM (1686-1761)

law ") is of rare occurrence . Haughtonite and siderophyllite are black varieties See also:

• RICH, BARNABE (c. 1540-1617)
• RICH, CLAUDIUS JAMES (1787-1821)
• RICH, JOHN (1692-1761)
• RICH, PENELOPE, LADY (c. 1562–1607)
• RICH, RICHARD, 1ST BARON RICH (1490?-1567)

rich in ferrous iron, and lepidomelane (from ?ten-is, a See also:

• SCALE
• SCALE (1) A

scale, and pEXas, black) is a variety rich in ferric iron . In barytobiotite and manganophyllite the magnesia is partly re-placed by baryta and manganous See also:

• OXIDE

oxide respectively .

Rubellane, hydrobiotite, pseudobiotite, and others are altered forms of biotite, which is a mineral particularly liable to decomposition with the See also:

• PRODUCTION (Lat. productionem, from producere, to pro-duce)

production of chlorites and vermiculites . Biotite is a See also:

• COMMON

common constituent of igneous and crystalline rocks: in See also:

• GRANITE (adapted from the Ital. granite, grained; Lat. granum, grain)

granite, See also:

• GNEISS

gneiss and See also:

• MICA

mica-schist it is often associated with See also:

• MUSCOVITE

muscovite (See also:

• WHITE
• WHITE, ANDREW DICKSON (1832– )
• WHITE, GILBERT (1720–1793)
• WHITE, HENRY KIRKE (1785-1806)
• WHITE, HUGH LAWSON (1773-1840)
• WHITE, JOSEPH BLANCO (1775-1841)
• WHITE, RICHARD GRANT (1822-1885)
• WHITE, ROBERT (1645-1704)
• WHITE, SIR GEORGE STUART (1835– )
• WHITE, SIR THOMAS (1492-1567)
• WHITE, SIR WILLIAM ARTHUR (1824--1891)
• WHITE, SIR WILLIAM HENRY (1845– )
• WHITE, THOMAS (1628-1698)
• WHITE, THOMAS (c. 1550-1624)

white mica), the two kinds having sometimes grown in parallel position . In volcanic rocks, and in nearly allother kinds of igneous rocks with the exception of granite, biotite occurs to the exclusion of the muscovite . In the dyke-rocks known as mica-traps or mica-See also:

• LAMPROPHYRES (from Gr. Xaurp6s, bright, and the terminal part of the word porphyry, meaning rocks containing bright porphyritic crystals)

lamprophyres biotite is especially abundant . It is also one of the most characteristic products of contact-See also:

• METAMORPHISM (Gr. ise-rci, change of, and liop¢i, shape)

metamorphism, being See also:

• DEVELOPED

developed in sedimentary and other rocks at their contact with granite masses . In the ejected blocks of crystalline See also:

• LIMESTONE

limestone of See also:

• MONTE

Monte Somma, See also:

• VESUVIUS (also Vesevus in ancient poets)

Vesuvius, the most perfectly developed crystals of biotite (figs . I, 2), or indeed of any of the micas, are found in abundance, associated with brilliant crystals of See also:

• AUGITE

augite, See also:

• OLIVINE

olivine, See also:

• HUMITE

humite, &c . Although biotite (black mica) is much more common and widely distributed than white mica, yet it is of far less economic importance . The small See also:

• SIZE

size of the sheets, their dark colour and want of transparency render the material of little value . Large, cleavable masses yielding See also:

• FINE

fine smoky-black and green sheets, sufficiently elastic for See also:

• INDUSTRIAL

industrial purposes, are, however, found in See also:

• RENFREW

Renfrew See also:

• COUNTY (through Norm. Fr. comae, cf. O. Fr. cunte, conk', Mod. Fr. comae, from Lat. comitatus, cf. Ital. comitato, Prov. comtat; see COUNT)

county, See also:

• ONTARIO
• ONTARIO, LAKE

Ontario . (L . J .