AMPHIBOLITE  , the name given to a 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 consisting mainly of See also:

• AMPHIBOLE

amphibole (See also:

• HORNBLENDE

hornblende), the use of the See also:

• TERM

term being restricted, however, to metamorphic rocks . Holocrystalline plutonic igneous rocks composed essentially of hornblende are known as hornblendites . As is the See also:

• CASE
• CASE, JOHN (d. 1600)

case with most petrological terms the exact See also:

• CONNOTATION

connotation is not very strictly defined; most authors allow that See also:

• ACCESSORY

accessory minerals such as See also:

• FELSPAR, or FELDSPAR

felspar, See also:

• GARNET
• GARNET, or GARNETT, HENRY (1555—1606)

garnet, See also:

• AUGITE

augite and See also:

• QUARTZ

quartz may be See also:

• PRESENT

present in variable and often considerable amount . A foliated or schistose structure, though often See also:

• DEVELOPED

developed in these rocks, is not universal . The hornblende 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 (actinolite) but may be nearly See also:

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

black in the See also:

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

hand specimen; in the microscopic slide it is commonly green of various shades, but may be 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, See also:

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

blue or nearly colourless . It frequently occurs in elongated bladed prisms, but rarely shows See also:

• GOOD, JOHN MASON (1764-1827)

good crystal faces . The term hornblende-schist is employed by many writers as nearly, synonymous with amphibolite; most hornblende-See also:

• SCHISTS (Gr. vxq'ecv, to split)

schists contain felspar and See also:

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

iron oxides, while See also:

• SPHENE

sphene, See also:

• RUTILE

rutile, quartz and See also:

• APATITE

apatite are rarely absent . Reddish garnets are often conspicuous in the rocks of this See also:

• GROUP

group (garnet-amphibolites), and when in addition a green-coloured augite occurs the rocks are intimately allied to the hornblende-eclogites . See also:

• EPIDOTE

Epidote also, in yellow grains, is See also:

• COMMON

common (epidote-amphibolites), and in these rocks the hornblende may be of the blue and richly pleochroic variety known as glaucophane (glaucophane-epidote-schists) . Hornblende-schists containing dark green ferriferous hornblende (grunerite-schists) are abundant in some parts of See also:

• NORTH
• NORTH, BARONS
• NORTH, MARIANNE (1830—1890)
• NORTH, ROGER (1653-1734)
• NORTH, SIR THOMAS (1535?-16o1?)

North See also:

• AMERICA

America . See also:

• TREMOLITE

Tremolite-schists consist essentially of 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 or very See also:

• PALE (through Fr. pal, from Lat. palms, a stake, for paglus, from the stem pag- of pangere, to fix; " pole " is from the same original source)

pale green amphibole; occasionally they are black from the presence of numerous See also:

• MINUTE
• MINUTE (Lat. minutes, small; minuere, to make less)

minute grains of iron See also:

• OXIDE

oxide or of See also:

• GRAPHITE

graphite . Many tremolite-schists contain much See also:

• TALC

talc and See also:

• CHLORITE

chlorite, and as these rocks have been derived from peridotites they not infrequently show residual grains of See also:

• OLIVINE

olivine .

Nephrite (Gr. vecpos, a See also:

• KIDNEY

kidney) is a very compact, hardly schistose amphibolite, consisting of See also:

• FINE

fine interwoven See also:

• FIBRES
• FIBRES (or FIBERS, in American spelling; from Lat. fibra, apparently connected either with filum, thread, or findere, to split)

fibres of hornblende . Among other accessory minerals See also:

• BIOTITE

biotite, chlorite, talc, See also:

• SCAPOLITE (Gr. O'Kairos, rod, )tLOoc, stone)

scapolite and See also:

• TOURMALINE

tourmaline may be mentioned; if abundant they give rise to See also:

• SPECIAL

special varieties such as biotite-amphibolite, &c . See also:

• AMPHIBOLOGY

AMPHIBOLOGY The amphibolites are typical rocks of the metamorphic group and as such attain a large development in all regions of crystalline schists and gneisses such as the See also:

• ALPS

Alps, See also:

• ARDENNES

Ardennes, Harz, Scottish See also:

• HIGHLANDS, THE

Highlands, and the Lakes See also:

• DISTRICT

district of North America . They occur in two ways, viz. as large circular or elliptical areas which See also:

• MARK
• MARK, CARL (1858– )
• MARK, GOSPEL OF ST
• MARK, ST

mark the site of old plutonic See also:

• STOCKS

stocks or bosses of basic rock, and as See also:

• LONG, GEORGE (1800-1879)
• LONG, JOHN DAVIS (1838– )

long narrow strips intercalated among outcrops of other metamorphic rocks . Regarded from the point of view of their origin they fall into two See also:

• GROUPS
• GROUPS, THEORY

groups, the ortho-amphibolites, which are modified igneous rocks, and the See also:

• PARA
• PARA (officially BELEM; sometimes BELEM DO PARA)

para-amphibolites, which are altered sediments . The former are far the more common . Igneous rocks which contain much augite (e.g. dolerites, gabbros, diabases, pyroxenites and many peridotites) are usually converted into amphibolites when they are subjected to pressure and interstitial movements during See also:

• EARTH
• EARTH (a word common to Teutonic languages, cf. Ger. Erde, Dutch aarde, Swed. and Dan. jord; outside Teutonic it appears only in the Gr. 'pq'e, on the ground; it has been connected by some etymologists with the Aryan root ar-, to plough, which is seen in
• EARTH, FIGURE OF
• EARTH, FIGURE OF THE

earth-folding . If felspar be present also, epidote may See also:

• FORM (Lat. forma)

form, while See also:

• PART

part of the felspar recrystallizes as a See also:

• SPECIES

species of the same See also:

• MINERAL

mineral richer in alkalies or as See also:

• MICA

mica . Olivine and See also:

• ILMENITE

ilmenite, the other common constituents of these rocks, may, alone or in See also:

• CONJUNCTION (from Lat. conjungere, to join together)

conjunction with the above-named minerals, yield garnet, talc, sphene, rutile, &c . There is little or no alteration in the bulk See also:

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

composition of the rock, but its component elements enter into new combinations . Chemical See also:

• ANALYSIS (Gr. avci and Meta, to break up into parts)

analysis, accordingly, will often enable us to identify an igneous rock (See also:

• DIABASE

diabase, &c.) under the See also:

• GUISE
• GUISE, HOUSE OF

guise of an amphibolite . The trans-formation of the rock may be See also:

• COMPLETE

complete, so that no trace is See also:

• LEFT

left of the See also:

• ORIGINAL

original structures or minerals .

Very often, however, it is only partial, and by obtaining a sufficiently large number of specimens a See also:

• SERIES (a Latin word from serere, to join)

series of intermediate or transitional stages may be studied; these prove conclusively the nature of the See also:

• PROCESS

process, though its causes are less clearly understood . Green hornblende may be seen gradually replacing augite, at first in See also:

• NEEDLE (O. Eng. ncedl; the word appears in various forms in Teutonic languages, Ger. Nadel, Dutch naal, the root being ne-, to sew, cf. Ger. nahen, and probably Lat. nere, to spin, Gr. vi)ats, spinning)

needle-like crystals, for which gradually more compact masses are substituted . The felspar breaks up into a See also:

• MOSAIC (corresponding to Lat. opus musivum, from Gr. µovoeiov, an artificial grotto often decorated with mosaics; the word is only found in the sense of mosaic in late Greek, which generally uses k oXI yrlµa)

mosaic in which See also:

• ALBITE

albite, epidote or See also:

• ZOISITE

zoisite, quartz and garnet may often be identified, Biotite and See also:

• PRIMARY

primary hornblende suffer comparatively little 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; olivine disappears, and garnet, talc and tremolite or anthophyllite take its See also:

• PLACE (through Fr. from Lat. platea, street; Gr. IrAar6s, wide)

place . The original structures of this group of rocks (ophitic, porphyritic, poikilitic, vesicular, &c.) gradually fade away, and See also:

• MERGE

merge into those of the metamorphic amphibolites . Even when the greater part of the rock See also:

• MASS (O.E. maesse; Fr. messe; Ger. Messe; Ital. messa; from eccl. Lat. missa)
• MASS, IN

mass has suffered complete reconstruction, kernels or phacoids may remain, showing the old igneous structures, though the minerals are greatly altered . The transitional stages from See also:

• GABBRO

gabbro or diabase to amphibolite are so common that they form a widespread and important group of rocks, which have been described under the names greenstone, greenstone-schist, flaser-gabbro, saussuritegabbro, See also:

• META

meta-diabase, &c . The ortho-amphibolites also include a small group of igneous rocks, which have a foliated or banded structure due to movements and pressure during consolidation, e.g. foliated See also:

• DIORITE (from the Gr. S&oi4eiv to distinguish, from hA through, Epos, a boundary)

diorite or diorite-schist . The sedimentary amphibolites or para-amphibolites, less common than those above described, are frequent in some districts, such as the See also:

• NORTHERN

northern Alps, See also:

• SOUTHERN

southern highlands of See also:

• SCOTLAND
• SCOTLAND, CHURCH OF
• SCOTLAND, EPISCOPAL CHURCH OF

Scotland, Green Mountains, U.S.A . Many of them have been ash-beds, and their See also:

• CONVERSION (Lat. conversio, from convertere, to turn or ,change)

conversion into hornblende-schists follows exactly similar stages to those exemplified by basic crystalline igneous rocks . Others have been greywackes of varied composition with epidote, chlorite, felspar, quartz, iron oxides, &c., and may have been mixed with volcanic materials, or may be partly derived from the disintegration of basic rocks . When they are most metamorphosed they are often very hard to distinguish from igneous hornblende-schists; yet they rarely fail to reveal signs of bedding, pebbly structure, sedimentary banding and See also:

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

gradual transition into undoubtedly sedimentary types of See also:

• GNEISS

gneiss and schist . Deposits containing See also:

• DOLOMITE

dolomite and siderite also readily yield amphibolites (tremolite-schists, grunerite-schists, &c.) especially where there has been a certain amount of contact See also:

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

metamorphism by adjacent granitic masses .

(J . S .