See also:

• SCHISTS (Gr. vxq'ecv, to split)

SCHISTS (Gr. vxq'ecv, to split)  , in See also:

• PETROLOGY

petrology, metamorphic rocks which have a fissile See also:

• CHARACTER (Gr. xapareri7p, from xap&crew, to scratch)

character . In all of them there is at least one See also:

• MINERAL

mineral which crystallizes in platy forms (e.g. See also:

• MICA

mica, See also:

• TALC

talc, See also:

• CHLORITE

chlorite, See also:

• HAEMATITE, or HEMATITE

haematite), or in See also:

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

long See also:

• BLADES, WILLIAM (1824-1890)

blades or See also:

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

fibres (anthophyllite, See also:

• TREMOLITE

tremolite, actinolite, See also:

• TOURMALINE

tourmaline), and, when these have a well marked parallel arrangement in definite bands or folia, 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 will break far more easily along the bands than across them . The platy minerals have also a perfect cleavage parallel to their See also:

• FLAT (a modification of O. Eng. flet, an obsolete word of Teutonic origin, meaning the ground beneath the feet)

flat surfaces, while the fibrous See also:

• SPECIES

species often have two or more cleavages following their long axes; hence a schistose rock may split not only by separation of the mineral plates from one another but also by cleavage of the parallel minerals through their substance . See also:

• SCHISTS (Gr. vxq'ecv, to split)

Schists in the See also:

• COMMON

common See also:

• ACCEPTANCE (Lat. acceptare, frequentative form of accipere, to receive)

acceptance of that See also:

• TERM

term are really highly crystalline rocks; fissile slates, shales or sandstones, in which the See also:

• ORIGINAL

original sedimentary structures are little modified by recrystallization, are not included in this See also:

• GROUP

group by See also:

• ENGLISH

English petrologists, though the See also:

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

French schistes and the See also:

• GERMAN
• GERMAN, DUTCH AND SCANDINAVIAN

German Schiefer are used to designate also rocks of these types . The difference between schists and gneisses is mainly that the latter have less highly See also:

• DEVELOPED

developed foliation; they also, as a See also:

• RULE

rule, are more coarse grained, and contain far more See also:

• QUARTZ

quartz and See also:

• FELSPAR, or FELDSPAR

felspar, two minerals which rarely assume platy or acicular forms, and hence do not See also:

• LEAD
• LEAD (pronounced iced)

lead to the See also:

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

production of a fissile character in the rocks in which they are important constituents . Schists, as a rule, are found in regions composed mainly of metamorphic rocks, such as the Central See also:

• ALPS

Alps, Himalayas, and other See also:

• MOUNTAIN (0. Fr. montaigne; popular Lat. montanea, an adjectival form from the classical mons, montis, whence Eng. " mount," a form usually used along with the name of an individual mountain, e.g. Mt Everest)
• MOUNTAIN, THE (La Montagne)

mountain ranges, See also:

• SAXONY
• SAXONY (Ger. Provinz Sachsen)

Saxony, Scandinavia, the See also:

• HIGHLANDS, THE

Highlands of See also:

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

Scotland and See also:

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

north-See also:

• WEST
• WEST, BENJAMIN (1738-1820)
• WEST, NICHOLAS (1461-1533)

west of See also:

• IRELAND
• IRELAND, CHURCH
• IRELAND, CHURCH OF
• IRELAND, JOHN (1761-1842)
• IRELAND, JOHN (1838- )
• IRELAND, WILLIAM HENRY (1777-1835)

Ireland . They are typical products of " regional " See also:

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

metamorphism, and are in nearly all cases older than the fossiliferous sedimentary rocks . Transitions between schists and normal igneous or sedimentary rocks are often found . The See also:

• SILURIAN

Silurian mica-schists of See also:

• BERGEN

Bergen in See also:

• NORWAY
• NORWAY (Norge)

Norway are fossiliferous; in the Alps it is believed that even Mesozoic rocks pass laterally into mica-schists and calc-schists . These changes are regarded as having been produced by the operation of See also:

• HEAT (0. E. haktu, which like " hot," Old Eng. hat, is from the Teutonic type haita, hit, to be hot; cf. Ger. hitze, heiss; Dutch, hitte, heet, &c.)

heat, pressure and folding . It is often taught that gneisses are the further stages of the See also:

• CRYSTALLIZATION

crystallization of schists and belong to a deeper See also:

• ZONE (Gr. 'WV77, a girdle, from 'wvvLvay to gird)

zone where the pressures and the temperatures were greater . Igneous rocks also may be converted readily into schists (e.g. See also:

• SERPENTINE

serpentine into talc-schist, See also:

• DOLERITE (from Gr. SoXepos, deceptive)

dolerite into See also:

• HORNBLENDE

hornblende-schist) by the same agencies .

There are two See also:

• GREAT

great See also:

• GROUPS
• GROUPS, THEORY

groups of schists, viz. those derived from sedimentary and those derived from igneous rocks, or, as they have been called, the " paraschists " and the " orthoschists." The first group is the more important and includes some of the commonest metamorphic rocks . In the paraschists, though fossils are exceedingly rare, sedimentary structures such as bedding and the See also:

• ALTERNATION (from Lat. alternare, to do by turns)

alternation of laminae of See also:

• FINE

fine and coarse See also:

• DEPOSIT (Lat. depositurn, from deponere, to lay down, to put in the care of)

deposit may frequently be preserved . The foliation is often parallel to the bedding, but may See also:

• CROSS

cross it obliquely or at right angles; or the bedding may be folded and contorted while the foliation maintains a nearly See also:

• UNIFORM

uniform See also:

• ORIENTATION

orientation . When the foliation is undulose or sinuous the rocks are said to be crumpled, and have wavy splitting surfaces instead of nearly See also:

• PLANE

plane ones . The development of foliation in shaly rocks is undoubtedly closely akin to the production of cleavage in slates . The sedimentary schists or paraschists have three great sub-divisions, the mica-schists and chlorite-schists (which correspond in a See also:

• GENERAL
• GENERAL (Lat. generalis, of or relating to a genus, kind or class)

general way to shales or See also:

• CLAY (from O. Eng. claeg, a word common in various forms to Teutonic languages, cf. Ger. Klei)
• CLAY, CASSIUS MARCELLUS (1810-1903)
• CLAY, CHARLES (1801–1893)
• CLAY, FREDERIC (1838–1889)
• CLAY, HENRY (1777–1852)

clay rocks) the calc-schists (impure limestones) and the quartz-schists (metamorphosed sandstones) . In the mica-schists of this group See also:

• BIOTITE

biotite or See also:

• MUSCOVITE

muscovite may be the See also:

• PRINCIPAL

principal mineral and often both are See also:

• PRESENT

present in varying proportions; the mica has developed from the argillaceous See also:

• MATTER

matter of the original rock; in addition there is always quartz and sometimes felspar (See also:

• ALBITE

albite or See also:

• OLIGOCLASE

oligoclase) . A large number of minerals may occur as accessories, e.g. See also:

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

garnet, tourmaline, See also:

• STAUROLITE

staurolite, See also:

• ANDALUSITE

andalusite, actinolite, chloritoid or ottrelite, See also:

• EPIDOTE

epidote, haematite, and if any of these is abundant its presence may be indicated by the name given the rock, e.g. staurolite-mica-schist . The phyllites (q.v.) See also:

• FORM (Lat. forma)

form a See also:

• MIDDLE

middle term between this group and the slates; they consist usually of quartz, 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 and chlorite, and have much of the foliation and schistosity of the mica-schists . Those rocks which contain andalusite and staurolite are sometimes found in such associations as show that they are due to contact See also:

• ACTION

action by intrusive igneous masses . The chlorite-schists are often of igneous derivation, such as ash-beds or fine lavas which have been metamorphosed . Many of them cpntain large octahedra of See also:

• MAGNETITE

magnetite .

Others are probably sedimentary rocks, especially those which contain much muscovite . Calc-schists are usually argillaceous limestones in which a large development of biotite or See also:

• PHLOGOPITE

phlogopite has occasioned foliation . Often they contain quartz and felspar, sometimes See also:

• PYROXENE

pyroxene, See also:

• AMPHIBOLE

amphibole, garnet or epidote . Pure limestones do not frequently take on schistose facies . The quartz-schists consist of quartz and white mica, and are intimately related to quartzites . Many of them have been originally micaceous or felspathic sandstones . We may mention also graphiticschists containing dark scaly See also:

• GRAPHITE

graphite (often altered forms of carbonaceous shales), and haematite-schists which may represent beds of ironstone . The orthoschists are white mica-schists produced by the shearing of See also:

• ACID (from the Lat. root ac-, sharp; acere, to be sour)

acid rocks, such as See also:

• FELSITE

felsite and See also:

• PORPHYRY (IlopcPisptos) (A.D. 233-c. 304)

porphyry . Some of the " porphyroids " which have grains of quartz and felspar in a finely schistose micaceous See also:

• MATRIX

matrix are intermediate between porphyries and micaschists of this group . Still more numerous are orthoschists of hornblendic character (hornblende-schists) consisting of 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 hornblende with often felspar, quartz and See also:

• SPHENE

sphene (also See also:

• RUTILE

rutile, garnet, epidote or See also:

• ZOISITE

zoisite, biotite and See also:

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

iron oxides) . These are modified forms of basic rocks such as See also:

• BASALT

basalt, dolerite and See also:

• DIABASE

diabase . Every transition can be found between perfectly normal ophitic dolerites and typical hornblende-schists, and occasionally the same See also:

• DIKE, or DYKE (Old Eng. dic, a word which appears in various forms in many Teutonic languages, cf. Dutch dijk, German Teich, Danish dige, and in French, derived from Teutonic, digue; it is the same word as " ditch " and is ultimately connected with the ro

dike or See also:

• SILL
• SILL (O.Eng. syl, Mid. E. sylle, selle; the word appears in Icel. syll, svill, Swed. syll, and Dan. syld, and in German, as Schwelle; Skeat refers to the Teutonic root swal-, swell, the word meaning the rise or swell formed by a beam at a threshold; the L
• SILL, EDWARD ROWLAND (1841-1887)

sill will provide specimens of all the connecting stages .

A few hornblendeschists are metamorphosed gabbros; others have developed from dikes or sills of lamprophyre . Under extreme crushing these basic rocks may be converted into dark biotite-schists, or greenish chloriteschists . Tremolite-schist and anthophyllite-schist are in nearly all cases the representatives of the ultra-basic igneous rocks such as See also:

• PERIDOTITE

peridotite in regions of high metamorphism . Talc-schists are of the same See also:

• CATEGORY (Gr. Karrlyopia, " accusation ")

category . They are soft and lustrous, with a peculiarly smooth feel, and though often confounded with mica-schists may be distinguished by their richness in See also:

• MAGNESIA

magnesia; many of them contain tremolite or actinolite; others have residual grains of See also:

• OLIVINE

olivine or See also:

• AUGITE

augite; and here also every gradation can be found between the unmodified igneous types and the perfectly metamorphic schists . Occasionally serpentines become sheared without yielding talcose minerals; they are then known as serpentine-schist and antigoriteschist, the latter being tough See also:

• LEEK

leek-green rocks, more or less trans-See also:

• PARENT, SIMON NAPOLEON (1855– )

parent .