See also:

• GREISEN (in French, hyalomicte)

GREISEN (in See also:

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

French, hyalomicte)  , a modification of See also:

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

granite, consisting essentially of See also:

• QUARTZ

quartz and 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 See also:

• MICA

mica, and distinguished from granite by the See also:

• ABSENCE (Lat. absentia)

absence of See also:

• FELSPAR, or FELDSPAR

felspar and See also:

• BIOTITE

biotite . In the See also:

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

hand specimen the 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 has a silvery glittering See also:

• APPEARANCE (from Lat. apparere, to appear)

appearance from the abundance of lamellar crystals of See also:

• MUSCOVITE

muscovite, but many greisens have much of the appearance of granite, except that they are paler in See also:

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

colour . The commonest See also:

• ACCESSORY

accessory minerals are See also:

• TOURMALINE

tourmaline, See also:

• TOPAZ

topaz, See also:

• APATITE

apatite, fluorspar and See also:

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

iron oxides; a little felspar more or less altered may also be See also:

• PRESENT

present and a 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 mica which is biotite or lithionite . The tourmaline in See also:

• SECTION
• SECTION (Lat. sectio, cutting, secare, to cut)

section is brown, 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, See also:

• BLUE (common in different forms to most European languages)

blue or colourless, and often the same crystal shows many different tints . The white mica forms mostly large plates with imperfect crystalline outlines . The quartz is 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 fluid enclosures . Apatite and topaz are both colourless and of irregular See also:

• FORM (Lat. forma)

form . Felspar if present may be See also:

• ORTHOCLASE

orthoclase and See also:

• OLIGOCLASE

oligoclase . See also:

• GREISEN (in French, hyalomicte)

Greisen occurs typically in belts or See also:

• VEINS

veins intersecting granite . At the centre of each vein there is usually a fissure which may be open or filled with quartz . The greisen bands are from I in. up to 2 ft. or more in thickness . At their See also:

• OUTER

outer edges they pars gradually into the granite, for they contain felspar crystals more or less completely altered into aggregates of white mica and quartz .

The transition between the two rocks is perfectly See also:

• GRADUAL (Med. Lat. gradualis, of or belonging to steps or degrees; gradus, step)

gradual, a fact which shows that the greisen has been produced by alteration of the granite . Vapours or fluids rising through the fissure have been the agents which effected the transmutation . They must have contained See also:

• FLUORINE (symbol F, atomic weight 19)

fluorine, See also:

• BORON (symbol B, atomic weight I I)

boron and probably also See also:

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

lithium, for topaz, mica and tourmaline, the new minerals of the granite, contain these elements . The See also:

• CHANGE (derived through the Fr. from the Late Lat. cambium, cambiare, to barter; the ultimate derivation is probably from the root which appears in the Gr. «a urmu', to bend)

change is a See also:

• POST

post-volcanic TI or pneumatolytic one induced by the vapours set See also:

• FREE

free by the granite magma when it cools . Probably the rock was at a relatively high temperature at the See also:

• TIME (0. Eng. Lima, cf. Icel. timi, Swed. timme, hour, Dan. time; from the root also seen in " tide," properly the time of between the flow and ebb of the sea, cf. O. Eng. getidan, to happen, " even-tide," &c.; it is not directly related to Lat. tempus)
• TIME, MEASUREMENT OF
• TIME, STANDARD

time . A similar type of alteration, the development of white mica, quartz and tourmaline, is found sometimes in sedimentary rocks around granite masses . Greisen is closely connected with See also:

• SCHORL

schorl rock both in its mineralogical See also:

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

composition and in its mode of origin . The latter is a pneumatolytic product consisting of quartz and tourmaline; it often contains white mica and thus passes by all stages into greisen . Both of these rocks carry frequently small percentages of See also:

• TIN (Lat.- stannum, whence the chemical symbol " Sn "; atomic weight =117.6, 0=16)

tin See also:

• OXIDE

oxide (cassiterite) and may be worked as ores of tin . They are See also:

• COMMON

common in See also:

• CORNWALL

Cornwall, See also:

• SAXONY
• SAXONY (Ger. Provinz Sachsen)

Saxony, See also:

• TASMANIA

Tasmania and other districts which are centres of tin-See also:

• MINING

mining . Many other greisens occur in which no tin is found . The analyses show the composition of Cornish granite and greisen .

They make it clear that there has been an introduction of fluorine and boron and a diminution in the alkalies during the transformation of the granitic rock into the greisen . (J . S .