PETROLOGY  , the See also:

• SCIENCE (Lat. scientia, from scire; to learn, know)

science of rocks (Gr. itrETpos), the See also:

• BRANCH (from the Fr. branche, late Lat. branca, an animal's paw)

branch of See also:

• GEOLOGY (from Gr. yp7, the earth, and Abyor, science)

geology which is concerned with the investigation of the See also:

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

composition, structure and See also:

• HISTORY

history of 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 masses which make up the accessible portions of the 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's crust . Rocks have been defined as " aggregates of minerals." They are the See also:

• UNITS, DIMENSIONS OF
• UNITS, PHYSICAL

units with which the geologist deals in investigating the structure of a See also:

• DISTRICT

district . Some varieties See also:

• COVER (from the Fr. convert, from couvrir, to cover, Lat. cooperire)

cover enormous areas and are among the commonest and most See also:

• FAMILIAR (through the Fr. familier, from Lat. familiaris, of or belonging to the familia, family)

familiar See also:

• OBJECTS

objects of nature . See also:

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

Granite, See also:

• SANDSTONE

sandstone, 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, See also:

• LIMESTONE

limestone, See also:

• SLATE (properly CLAY SLATE; in M. Eng. slat or sclat, from O. Fr. esclat, a small piece of wood used as a tile; esclater, to break into pieces, whence modern Fr. eclat, the root being seen also in Ger. schleissen, to split)

slate often See also:

• FORM (Lat. forma)

form whole provinces and build up lofty mountains . Such unconsolidated materials as See also:

• SAND
• SAND, GEORGE (1804-1876)

sand, See also:

• GRAVEL, or PEBBLE BEDS

gravel, clay, See also:

• SOIL

soil are justly included among rocks as being See also:

• MINERAL

mineral masses which See also:

• PLAY

play an important role in See also:

• FIELD (a word common to many West German languages, cf. Ger. Feld, Dutch veld, possibly cognate with O.E. f olde, the earth, and ultimately with root of the Gr. irAaror, broad)
• FIELD, CYRUS WEST (1819-1892)
• FIELD, DAVID DUDLEY (18o5-1894)
• FIELD, EUGENE (1850-1895)
• FIELD, FREDERICK (18o1—1885)
• FIELD, HENRY MARTYN (1822-1907)
• FIELD, JOHN (1782—1837)
• FIELD, MARSHALL (183 1906)
• FIELD, NATHAN (1587—1633)
• FIELD, STEPHEN JOHNSON (1816-1899)
• FIELD, WILLIAM VENTRIS FIELD, BARON (1813-1907)

field geology . Other rock See also:

• SPECIES

species are of rare occurrence and may be known in only one or two localities in distant parts of the earth's See also:

• SURFACE

surface . Nearly all rocks consist of minerals, whether in a crystalline or non-crystalline See also:

• STATE
• STATE, GREAT OFFICERS OF

state, but the insoluble and imperishable parts of the skeletons of animals and See also:

• PLANTS

plants may constitute a considerable portion of rocks, as for example, See also:

• CORAL

coral limestone, See also:

• LIGNITE (Lat. lignum, wood)

lignite beds and See also:

• CHALK

chalk . Treatment of the Subject.—In this See also:

• PARAGRAPH

paragraph the subject See also:

• MATTER

matter of the science of petrology is briefly surveyed; the See also:

• OBJECT

object is to point out the headings under which particular subjects are treated (there is a See also:

• SEPARATE

separate See also:

• ARTICLE (from Lat. articulus, a joint)

article on the terms printed in italics) . See also:

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

General questions as to the nature, origin and See also:

• CLASSIFICATION (Lat. classis, a class, probably from the root cal-, cla-, as in Gr. icaMce, clamor)

classification of rocks and the methods of examination are discussed in the See also:

• PRESENT

present article; See also:

• MINERALOGY

mineralogy comprises similar matter respecting the component minerals; See also:

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

metamorphism, See also:

• METASOMATISM (Gr. /sera, change, o-wµa, body)

metasomatism, See also:

• PNEUMATOLYSIS (Gr. 7rvevµa, vapour, and Mete, to set free)

pneumatolysis and theformation of concretions are agencies which effect rocks and modify them . Three classes of rocks are recognized: the igneous, sedimentary and metamorphic . The plutonic, or deep-seated rocks, which cooled far below the surface, and occur as batholites, bosses, laccolites, and See also:

• VEINS

veins, include the See also:

• GREAT

great classes granite, See also:

• SYENITE

syenite, See also:

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

diorite, See also:

• GABBRO

gabbro and See also:

• PERIDOTITE

peridotite; related to the granites are See also:

• APLITE

aplite, See also:

• GREISEN (in French, hyalomicte)

greisen, See also:

• PEGMATITE (from Gr. 1r3 y ea, a bond)

pegmatite, See also:

• SCHORL

schorl rock and micropegmatite; to the syenites, See also:

• BOROLANITE

borolanite, See also:

• MONZONITE

monzonite, See also:

• NEPHELINE

nepheline-syenite and See also:

• IJOLITE (derived from the first syllable of the Finnish words Jiwaru, Jijoki, &c., common as geographical names in the Kola peninsula, and the Gr. XLOos, a stone)

ijolite; to the diorites, See also:

• APHANITE

aphanite, napolecnite and See also:

• TONALITE

tonalite; to the gabbros, See also:

• PYROXENITE

pyroxenite and See also:

• THERALITE (Gk. 9rlpav, to pursue)

theralite, and to peridotites, See also:

• PICRITE (from Gr. 7rsKpos, bitter, because these rocks are rich in magnesia, a base which forms bitter salts)

picrite and See also:

• SERPENTINE

serpentine . The hypabyssal intrusive rocks, occurring as sills, veins, dikes, necks, &c., are represented by See also:

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

porphyry and porphyrite (including See also:

• BOSTONITE

bostonite, See also:

• FELSITE

felsite and See also:

• QUARTZ

quartz-porphyry), See also:

• DIABASE

diabase and lamprophyre; some pitchstones belong to this See also:

• GROUP

group and contain crystallites and See also:

• SPHERULITES (Gr. cchaipa, sphere, Mhos, stone)

spherulites .

The volcanic rocks, found typically as See also:

• LAVA

lava flows, include See also:

• RHYOLITE (Gr. peiv, to flow, because of the frequency with which they exhibit fluxion structures)

rhyolite and See also:

• OBSIDIAN

obsidian (with. sometimes See also:

• PERLITE, or PEARLSTONE

perlite), See also:

• TRACHYTE (Gr. rpaxus, rough)

trachyte and See also:

• PHONOLITE (Gr. ~vi7, sound, and Moos, stone)

phonolite (and leucitophyre which is treated under See also:

• LEUCITE

leucite), See also:

• ANDESITE

andesite and See also:

• DACITE (from Dacia, mod. Transylvania)

dacite, See also:

• BASALT

basalt (with the related See also:

• DOLERITE (from Gr. SoXepos, deceptive)

dolerite, variolite and tachylyte), nephelinite and tephrite . Among sedimentary rocks we recognize a volcanic group (including See also:

• TUFF (Ital. tufo)

tuff, See also:

• AGGLOMERATE (from the Lat. agglomerare, to form into a ball, glomus, glomeris)

agglomerate and some kinds of See also:

• PUMICE (Lat. purnex, spumex, spuma, froth)

pumice) ; an arenaceous See also:

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

series such as sand (some with See also:

• GLAUCONITE

glauconite), sandstone, See also:

• QUARTZITE

quartzite, See also:

• GREYWACKE, or GRAUWACKE (a German word signifying a grey earthy rock)

greywacke and gravel; an argillaceous group including clay, See also:

• FIREBRICK

firebrick, See also:

• PHYLLITE (Gr. 40)XAov, a leaf, probably because they yield leaf-like plates, owing to their fissility)

phyllite, See also:

• LATERITE (Lat. later, a brick)

laterite shale and slate; a calcareous series with chalk, limestone (often forming See also:

• STALACTITES (Gr. (rraXaicros, from vraXaQVecv, to drip)

stalactites and stalagmites), See also:

• DOLOMITE

dolomite and marls or argillaccous limestones (See also:

• FLINT
• FLINT, AUSTIN (1812-1886)
• FLINT, or FLTNTSHTRE (sir Gallestr)
• FLINT, ROBERT (1838- )
• FLINT, TIMOTHY (1780-1840)

flint occurs as nodules in chalk) ; the natural See also:

• PHOSPHATES

phosphates may be mentioned here . The metamorphic rocks are commonly gneisses and See also:

• SCHISTS (Gr. vxq'ecv, to split)

schists (including See also:

• MICA

mica-schist) ; other types are See also:

• AMPHIBOLITE

amphibolite, See also:

• CHARNOCKITE

charnockite, See also:

• ECLOGITE (from Gr. EKXoyi, a selection)

eclogite, See also:

• EPIDIORITE

epidiorite, See also:

• EPIDOSITE

epidosite, granulate, See also:

• ITACOLUMITE

itacolumite, See also:

• HORNFELS (a German word meaning hornstone)

hornfels, See also:

• MYLONITE (Gr. iwXwv, a mill)

mylonite and the See also:

• SEA (in O. Eng. sae, a common Teutonic word; cf. Ger. See, Dutch Zee, &c.; the ultimate source is uncertain)
• SEA, COMMAND OF THE

sea polite rocks . Composition.—Only the commonest minerals are of importance as rock formers . Their number is small, not exceeding a hundrod in all, and much less than this if we do not reckon the subdivisions into which the commoner species are broken up . The vast See also:

• MAJORITY (Fr. majorite; Med. Lat. majoritas; Lat. major, greater)

majority of the rocks which we see around us every See also:

• DAY (O. Eng. dreg, Ger. Tag; according to the New English Dictionary, " in no way related to the Lat. dies")
• DAY, JOHN (1574-1640?)
• DAY, THOMAS (1748-1789)

day consist of quartz, See also:

• FELSPAR, or FELDSPAR

felspar, mica, See also:

• CHLORITE

chlorite, See also:

• KAOLIN

kaolin, See also:

• CALCITE

calcite, See also:

• EPIDOTE

epidote, See also:

• OLIVINE

olivine, See also:

• AUGITE

augite, See also:

• HORNBLENDE

hornblende, See also:

• MAGNETITE

magnetite, See also:

• HAEMATITE, or HEMATITE

haematite, See also:

• LIMONITE, or BROWN IRON ORE

limonite and a few other minerals . Each of these has a recognized position in the See also:

• ECONOMY

economy of nature . A See also:

• MAIN (from the Aryan root which appears in " may " and " might," and Lat. magnus, great)
• MAIN (Lat. Moenus)

main determining See also:

• FACTOR (from Lat. facere, to make or do)

factor is the chemical composition of the See also:

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

mass, for a certain mineral can be formed only when the necessary elements are present in the rock . Calcite is commonest in limestones, as these consist essentially of carbonate of See also:

• LIME
• LIME (O. Eng. lim, Lat. limes, mud, from linere, to smear)

lime; quartz in sandstones and in certain igneous rocks which contain a high percentage of See also:

• SILICA

silica . Other factors are of equal importance in determining the natural association or paragenesis of rock-making minerals, principally the mode of origin of the rock and the stages through which it has passed in attaining its present See also:

• CONDITION (Lat. condicio, from condicere, to agree upon, arrange; not connected with conditio, from condere, conditum, to put together)

condition . Two rock masses may have very much the same bulk composition and yet consist of entirely different assemblages of minerals . The tendency is always for those compounds to be formed which are See also:

• STABLE

stable under the conditions under which the rock mass originated .

A granite arises by the consolidation of a molten magma (a fused rock mass; Gr . µfiy,ua, from µaaaety, to knead) at high temperatures and great pressures and its component minerals are such as are formed in such circumstances . Exposed to moisture, carbonic See also:

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

acid and other subaerial agents at the See also:

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

ordinary temperatures of the earth's surface, some of these See also:

• ORIGINAL

original minerals, such as 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 mica are permanent and remain unaffected; others " See also:

• WEATHER (O. Eng. weder; the word is common to Teutonic languages; cf. Du. weder, Dan. veir, Icel. ve8r, and Ger. Wetter and Gewitter, storm; the root is wa- to blow, from which is derived " wind ")

weather " or decay and are replaced by new combinations . The felspar passes into kaolin, See also:

• MUSCOVITE

muscovite and quartz, and if any See also:

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

black mica (See also:

• BIOTITE

biotite) has been present it yields chlorite, epidote, See also:

• RUTILE

rutile and other substances . These changes are accompanied by disintegration, and the rock falls into a loose, incoherent, earthy mass which may be regarded as a sand or soil . The materials thus formed may be washed away and deposited as a sandstone or grit . The structure of the original rock is now replaced by a new one; the mineralogical constitution is profoundly altered; but the bulk chemical composition may not be very different . The sedimentary rock may again undergo a See also:

• METAMORPHOSIS

metamorphosis . If penetrated by igneous rocks it may be recrystallized or, if subjected to enormous pressures with 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 and See also:

• MOVEMENT

movement, such as attend the See also:

• BUILDING

building of folded 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 chains, it may be converted into a See also:

• GNEISS

gneiss not very different in mineralogical composition though radically different in structure to the granite which was its original state . Structure.—The two factors above enumerated, namely the chemical and mineral composition of rocks, are scarcely of greater importance than their structure, or the relations of the parts of which they consist to one another . Regarded from this standpoint rocks may be divided into the crystalline and the fragmental . Inorganic matter, if See also:

• FREE

free to take that See also:

• PHYSICAL

physical Crystalline state in which it is most stable, always tends to Rocks. crystallize .

Crystalline rock masses have See also:

• CON

con- solidated from See also:

• SOLUTION (from Lat. solvere, to loosen, dissolve)

solution or from See also:

• FUSION

fusion . The vast majority of igneous rocks belong to this group and the degree of perfection in which they have attained the crystalline state depends primarily on the conditions under which they solidified . Such rocks as granite, which have cooled very slowly and under great pressures, have completely crystallized, but many lavas were poured out at the surface and cooled very rapidly; in this latter group a small amount of non-crystalline or glassy matter is frequent . Other crystalline rocks such as rock-See also:

• SALT (a common Teutonic word, cf. Dutch zout, Ger. Salz, Scand. salt; cognate with Gr. &Xs, Lat. sal)
• SALT, SIR TITUS, BART

salt, See also:

• GYPSUM

gypsum and See also:

• ANHYDRITE

anhydrite have been deposited from solution in See also:

• WATER

water, mostly owing to evaporation on exposure to the See also:

• AIR (from an Indo-European root meaning " breathe," " blow ")
• AIR, or ASBEN

air . Still another group, which includes the See also:

• MARBLES

marbles, mica-schists and quartzites, are recrystallized, that is to say, they were at first fragmental rocks, like limestone, clay and sandstone and have never been in a molten condition nor entirely in solution . Certain agencies however, acting on them, have effaced their See also:

• PRIMITIVE

primitive structures, and induced See also:

• CRYSTALLIZATION

crystallization, This is a See also:

• KIND (O. E. ge-cynde, from the same root as is seen in " kin," supra)

kind of metamorphism . The fragmental structure needs little explanation; wherever rocks disintegrate fragments are produced which are suitable for the formation of new rocks of this group . The original materials may be organic (shells, See also:

• CORALS (KoRAis), ADAMANTIOS [in French, DIAMANT CORAY] (1748–1833)

corals, plants) or vitreous (volcanic glasses) or crystalline (granite, See also:

• MARBLE (from Lat. marmor, Gr. pApµapos, shining stone)

marble, &c.); the pulverizing See also:

• AGENT (from Lat. agere, to act)

agent may be See also:

• FROST (a common Teutonic word, cf. Dutch, vorst, Ger. Frost, from the common Teutonic verb meaning " to freeze," Dutch, vriezcn, Ger. frieren; the Indo-European root is seen in Lat. pruina, hoar-frost, cf. prurire, to itch, burn, pruna, burning coal, Sans
• FROST, WILLIAM EDWARD (1810–1877)

frost, See also:

• RAIN (O.E. regn; the word is common to Teutonic languages, cf. Ger. Regen, Swed. and Dan. regn; it has been connected with Lat. rigare, to wet, Gr. 13pixeav)

rain, See also:

• RUNNING

running water, or the See also:

• STEAM
• STEAM (0. Eng. steam, vapour, smoke, cf. Du. steam; the origin is unknown)

steam explosions which shatter the lava within a volcanic See also:

• CRATER

crater and produce the fragmental rocks known as volcanic ash, tuffs and agglomerates . The materials may be loose and incoherent (sand, clay, gravel) or compacted by pressure and the See also:

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

deposit of cementing substances by percolating water (sandstone, shale, See also:

• CONGLOMERATE (from the Lat. conglomerare, to form into a ball, glomus, glomeris; so also the general term " conglomeration " for a miscellaneous collection of things, gathered together in a mass)

conglomerate) . The grains of which fragmental rocks are composed may be coarse or See also:

• FINE

fine, fresh or decayed, See also:

• UNIFORM

uniform or diverse in their composition; the one feature which gives unity to the class is the fact that they are all derived from pre-existing rocks or organisms . Because they are made up of broken pieces these rocks are often said to be " elastic." Origin of Rocks.—The study of the structure of rocks evidently leads us to another method of regarding them, which is more fundamental than those enumerated above, as the structure depends on the mode of origin . Rocks are divided into three great classes, the Igneous, the Sedimentary and the Metamorphic .

The igneous (See also:

• LAT

Lat. ignis, See also:

• FIRE (in O. Eng. f j'r; the word is common to West German languages, cf. Dutch vuur, Ger. Feuer; the pre-Teutonic form is seen in Sanskrit pu, pavaka, and Gr. irup; the ultimate origin is usually taken to be a root meaning to purify, cf. Lat. purus)

fire) rocks have all consoli- dated from a state of fusion . Some of them are crystalline or " massive "; others are fragmental . The massive igneous rocks include a few which are nearly com- pletely vitreous, and still more which contain a small amount of amorphous matter, but the majority are completely crystal- lized . Among the best known examples are obsidian, pumice, basalt, trachyte, granite, diorite . The fragmental igneous rocks consist of volcanic ashes more or less firmly compacted . The sedimentary rocks form a second group; they sedimentary have all been laid down as deposits on the earth's Rocks . surface subject to the conditions of temperature, moisture and pressure which obtain there . They include fragmental and crystalline varieties . The former consist of the debris of pre-existing rocks, accumulated in seas, lakes or dry See also:

• LAND

land and more or less indurated by pressure and cementing substances . Gravel, sand and clay, conglomerate, sandstone, shale are well-known examples . Many of them are fossiliferous as they contain fragments of organisms . Some are very largely made up of remains of animals or plants, more or less altered by mineralization .

These are sometimes placed into a See also:

• SPECIAL

special group as rocks of organic origin; limestone, See also:

• PEAT (possibly connected with Med. Lat. petia, pecia, piece, ultimately of Celtic origin; cf. O. Celt. pet, O. Ir. pit, Welsh peth, portion)

peat and See also:

• COAL

coal are typical of this class . The crystalline sediments are such as rock-salt and gypsum, deposits of saline lakes or isolated portions of the sea . They were formed under conditionsunfavourable to See also:

• LIFE

life and hence rarely contain fossils . The metamorphic rocks are known to be almost entirely altered igneous or sedimentary masses . Metamorphism consists in the destruction of the original structures Metamorphtc Rocks. and the development of new minerals . The chemical composition of the rocks however suffers 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 . The rock becomes as a See also:

• RULE

rule more crystalline; but all stages in the See also:

• PROCESS

process may be found and in a metamorphosed sediment, e.g. a sandstone, remains of the original sand grains and See also:

• PRIMARY

primary fragmental structure may be observed, although extensive recrystallization has taken See also:

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

place . The agencies which produce metamorphism are high temperatures, pressure, interstitial moisture and in many cases movement . The effects of high temperatures are seen best in the rocks surrounding great out-crops of intrusive granite, for they have been baked and crystallized by the heat of the igneous rock (thermo-metamorphism) . In folded mountain chains where the strata have been greatly compressed and their particles have been forced to move over one another a different type of metamorphism prevails (regional or dynamic metamorphism) . Methods of Investigation.—The macroscopic (Gr. garcpos, large) characters of rocks, those visible in See also:

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

hand-specimens without the aid of the See also:

• MICROSCOPE (Gr. µucp6s, small, asenreiv, to %view)

microscope, are very varied and Macroscopic difficult to describe accurately and fully . The characters .

geologist in the field depends principally on them and on a few rough chemical and physical tests; and to the See also:

• PRACTICAL

practical engineer, architect and See also:

• QUARRY

quarry-See also:

• MASTER (Lat. magister, related to tnagis, more, as the corresponding minister is to minus, less; the English form is due partly to the O. Eng. maegister, and partly to O. Fr. maistre, mod. maitre; cf. Du. meester, Ger. Meister, Ital. maestro)

master they are all-important . Although frequently insufficient in themselves to determine the true nature of a rock, they usually serve for a preliminary classification and often give all the See also:

• INFORMATION (from Lat. informare, to give shape or form to, to represent, describe)

information which is really needed . With a small See also:

• BOTTLE (Fr. bouteille, from a diminutive of the Lat. butta, a flask; cf. Eng. " butt ")

bottle of acid to test for carbonate of lime, a See also:

• KNIFE (0. E. cuff, a word appearing in different forms in many Teutonic languages, cf. Du. knijf, Ger. Kneif, a shoe-maker's knife, Swed. knif; the ultimate origin is unknown; Skeat finds the origin in the root of " nip," formerly " knip "; Fr. canif is a

knife to ascertain the hardness of rocks and minerals, and a See also:

• POCKET

pocket See also:

• LENS
• LENS (from Lat. lens, lentil, on account of the similarity of the form of a lens to that of a lentil seed)

lens to magnify their structure, the field geologist is rarely at a loss to what group a rock belongs . The fine grained species are often indeterminable in this way, and the See also:

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

minute mineral components of all rocks can usually be ascertained only by microscopic examination . But it is easy to see that a sandstone or grit consists of more or less rounded, waterworn sand-grains and if it contains dull, weathered particles of felspar, shining scales of mica or small crystals of calcite these also rarely See also:

• ESCAPE (in mid. Eng. eschape or escape, from the O. Fr. eschapper, modern echapper, and escaper, low Lat. escapium, from ex, out of, and cappa, cape, cloak; cf. for the sense development the Gr. iichueoOat, literally to put off one's clothes, hence to sli

escape observation . Shales and clay rocks generally are soft, fine grained, often laminated and not infrequently contain minute organisms or fragments of plants . Limestones are easily marked with a knife-blade, effervesce readily with weak See also:

• COLD (in O. Eng. cald and ceald, a word coming ultimately from a root cognate with the Lat. gelu, gelidus, and common in the Teutonic languages, which usually have two distinct forms for the substantive and the adjective, cf. Ger. Kolte, kalt, Dutch koude

cold acid and often contain entire or broken shells or other fossils . The crystalline nature of a granite or basalt is obvious at a glance, and while the former contains white or See also:

• PINK

pink felspar, clear vitreous quartz and glancing flakes of mica, the other will show yellow-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 olivine, black augite and See also:

• GREY, CHARLES GREY, 2ND EARL (1764-1845)
• GREY, HENRY GREY, 3RD EARL (1802-1894)
• GREY, LADY JANE (1537-1554)
• GREY, SIR EDWARD
• GREY, SIR GEORGE (1812–1898)

grey striated See also:

• PLAGIOCLASE

plagioclase . But when dealing with unfamiliar types or with rocks so fine grained that their component minerals cannot be determined with the aid of a lens, the geologist is obliged to have recourse to more delicate and searching methods of investigation . With the aid of the See also:

• BLOWPIPE

blowpipe (to test the fusibility of detached crystals), the See also:

• GONIOMETER (from Gr. ytavia, angle, and d rpov, measure)

goniometer, the magnet, the magnifying See also:

• GLASS
• GLASS (O.E. glees, cf. Ger. Glas, perhaps derived from an old Teutonic root gla-, a variant of glo-, having the general sense of shining, cf. " glare," " glow ")
• GLASS, STAINED

glass and the specific gravity See also:

• BALANCE (derived through the Fr. from the Late Lat. bilantia, an apparatus for weighing, from bi, two, and lanx, a dish or scale)

balance, the earlier travellers attained surprisingly accurate results . Examples of these may be found in the See also:

• WORKS

works of von See also:

• BUCH
• BUCH, CHRISTIAN LEOPOLD VON, BARON (1774-1853)

Buch, See also:

• SCROPE
• SCROPE, GEORGE JULIUS POULETT (1797—1876)

Scrope, See also:

• DARWIN, CHARLES ROBERT (1809-1882)
• DARWIN, ERASMUS (1731-1802)

Darwin and many others . About the end of the 18th See also:

• CENTURY (from Lat. centuria, a division of a hundred men)

century, See also:

• DOLOMIEU

Dolomieu examined crushed rock powders under the microscope and Cordier in 1815 crushed, levigated and investigated the finer ground-mass of igneous rocks .

His researches are See also:

• MODELS

models of scrupulous accuracy, and he was able to announce that they consisted essentially of such minerals as felspar, augite, See also:

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

iron ores and volcanic glass, and did not differ in nature from the coarser grained rocks . See also:

• NICOL, JAMES (1810-1879)
• NICOL, WILLIAM

Nicol, whose name is associated with the See also:

• DISCOVERY

discovery of the Nicol's See also:

• PRISM (Gr. rrpivµa, properly a thing sawn, Irpii"ety, to saw)

prism, seems to have been the first to prepare thin slices of mineral substances, and his methods were applied by See also:

• WITHAM

Witham (1831) to the study of plant petrifactions . This method, of such far-reaching importance in petrology, was not at once made use of for the systematic Fragmental Rocks . Igneous Rocks . Microscopic Characters . refractive See also:

• INDEX

index of the mineral by comparison with those of different mounting See also:

• MEDIA

media . Further information is obtained by inserting the polarizer and rotating the See also:

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

section . The See also:

• LIGHT

light vibrates now only in one See also:

• PLANE

plane, and in passing through doubly refracting crystals in the Pleochroslide is, speaking generally, broken up into two rays, ism which vibrate at right angles to one another . In many coloured minerals such as biotite, hornblende, See also:

• TOURMALINE

tourmaline, chlorite, these two rays have different See also:

• COLOURS, MILITARY

colours, and when a section containing any of these minerals is rotated the change of See also:

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

colour is often very striking . This See also:

• PROPERTY

property, known as " pleochroism " (Gr. irXelwv, more; xpwr, colour), is of great value in the determination of rock-making minerals . It is often especially intense in small spots which surround minute enclosures of other minerals, such as See also:

• ZIRCON

zircon and epidote; these are known as " pleochroic halos." If the analyser be now inserted in such a position that it is crossed relatively to the polarizer the field of view will be dark where there are no minerals, or where the light passes through isotro- See also:

• DOUBLE
• DOUBLE (from the Mid. Eng. duble, the form which gives the present pronunciation, through the Old Er. duble, from Lat. duplus, twice as much)

Double See also:

• PIE

pie substances such as glass, liquids and cubic crystals . See also:

• REFRACTION
• REFRACTION (Lat. refringere, to break open or apart)

Refraction .

All other crystalline bodies, being doubly refracting, will appear See also:

• BRIGHT, JOHN (1811-188g)
• BRIGHT, SIR CHARLES TILSTON

bright in some position as the See also:

• STAGE (Fr. 6/age; from Lat. stare, to stand)

stage is rotated . The only exception to this rule is provided by sections which are perpendicular to the optic axes of birefringent crystals; these remain dark or nearly dark during a whole rotation, and as will be seen later, their investigation is of special importance . The doubly refracting mineral sections, however, will in all cases appear black in certain positions as the stage is Extinction. rotated . They are said to be " extinguished " when this takes place . If we See also:

• NOTE
• NOTE (Lat. nota, mark, sign, from noscere, to know)

note these positions we may measure the 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 between them and any cleavages, faces or other structures of the crystal by means of the rotating stage . These angles are characteristic of the See also:

• SYSTEM

system to which the mineral belongs and often of the mineral species itself (see See also:

• CRYSTALLOGRAPHY
• CRYSTALLOGRAPHY (from the Gr. Kpbo TaXXO , ice, and -ypachew, to write)

CRYSTALLOGRAPHY) . To facilitate measurement of extinction angles various kinds of eyepieces have been devised, some having a stauroscopic calcite See also:

• PLATE

plate, others with two or four plates of quartz cemented together; these are often found to give more exact results than are obtained by observing merely the position in which the mineral section is most completely dark between crossed nicols . The mineral sections when not extinguished are not only bright but are coloured and the colours they show depend on several factors, the most important of which is the strength of the double refraction . If all the sections are of the same thickness as is nearly true of well-made slides, the minerals with strongest double refraction yield the highest polarization colours . The See also:

• ORDER
• ORDER (through Fr. ordre, for earlier ordene, from Lat. ordo, ordinis, rank, service, arrangement; the ultimate source is generally taken to be the root seen in Lat. oriri, rise, arise, begin; cf. " origin ")
• ORDER, HOLY

order in which the colours are arranged is that known as See also:

• NEWTON
• NEWTON, ALFRED (1829–1907)
• NEWTON, JOHN (1725-1807)
• NEWTON, JOHN (1823-1895)
• NEWTON, SIR CHARLES THOMAS (1816-1894)
• NEWTON, SIR ISAAC (1642-1727)

Newton's See also:

• SCALE
• SCALE (1) A

scale, the lowest being dark grey, then grey, white, yellow, See also:

• ORANGE
• ORANGE (Citrus Aurantium)
• ORANGE, HOUSE OF

orange, red, See also:

• PURPLE

purple, See also:

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

blue and so on . The difference between the refractive indexes of the ordinary and the extraordinary See also:

• RAY (Lat. raia)
• RAY (or WRAY, as he wrote his name till 1670), JOHN (1628-1705)

ray in quartz is .009, and in a rock-section about aka of an See also:

• INCH (O. Eng. ynce from Lat. uncia, a twelfthpart; cf. " ounce," and see As)

inch thick this mineral gives grey and white polarization tints; nepheline with weaker double refraction gives dark grey; augite on the other hand will give red and blue, while calcite with still stronger double refraction will appear pinkish or greenish white . All sections of the same mineral, however, will not have the same colour; it was stated above that sections perpendicular to an optic See also:

• AXIS (Lat. for " axle ")

axis will be nearly black, and, in general, the more nearly any section approaches this direction the See also:

• LOWER

lower its polarization colours will be .

By taking the See also:

• AVERAGE

average, or the highest colour given by any mineral, the relative value of its double refraction can be estimated; or if the thickness of the section be precisely known the difference between the two refractive indexes can be ascertained . If the slides be thick the colours will be on the whole higher than in thin slides . It is often important to find out whether of the two axes of See also:

• ELASTICITY

elasticity (or vibration traces) in the section is that of greater elasticity (or lesser refractive index) . The quartz See also:

• WEDGE (O. Eng. wecg, a mass of metal, cognate with Dutch wig, wigge, Dan. vaegge, &c.; in Lith. the cognate form outside Teut. is found in wagis, a peg, spigot; there is no connexion with " weigh," " weight," which must be referred to the root wegh, to li

wedge or selenite plate enables us to do this . Suppose a doubly refracting mineral section so placed that it is " extinguished "; if now it is rotated through 45° it will be brightly illuminated . If the quartz wedge be passed across it so that the See also:

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

long axis of the wedge is parallel to the axis of elasticity in the section the polarization colours will rise or fall . If they rise the axes of greater elasticity in the two minerals are parallel; if they sink the axis of greater elasticity in the one is parallel to that of lesser elasticity in the other . In the latter See also:

• CASE
• CASE, JOHN (d. 1600)

case by pushing the wedge sufficiently far See also:

• COMPLETE

complete darkness or See also:

• COMPENSATION (from Lat. compensare, to weigh one thing against another)

compensation will result . Selenite wedges, selenite plates, mica wedges and mica plates are also used for this purpose . A quartz wedge also may be calibrated by determining the amount of double refraction in all parts of its length . If now it be used to produce compensation or complete extinction in any doubly refracting mineral section, we can ascertain what is the strength of the double refraction of the section because it is obviously equal and opposite to that of a known See also:

• PART

part of the quartz wedge . A further refinement of microscopic methods consists of the use of strongly convergent polarized light (konoscopic methods) .

This is obtained by a wide angled achromatic See also:

• CONDENSER

condenser above the polarizer, and a high See also:

• POWER [WILLIAM GRATTAN] TYRONE (1797-1841)

power microscopic See also:

• OBJECTIVE, or OBJECT GLASS

objective . Those sections are most useful which are perpendicular to an optic axis, and consequently remain dark on rotation . If they belong to uniaxial crystals they show a dark See also:

• CROSS

cross or convergent light between crossed nicols, investigation of rocks, and it was not till 1858 that Sorby pointed out its value . Meanwhile the See also:

• OPTICAL

optical study of sections of crystals had been advanced by See also:

• SIR

Sir See also:

• DAVID
• DAVID (a Hebrew name meaning probably beloved 1)
• DAVID, FELICIEN (1810—1876)
• DAVID, GERARD [GHEERAERT DAVIT], (?=1523)
• DAVID, PIERRE JEAN (1789–1856)
• DAVID, ST (Dewi, Sant)

David See also:

• BREWSTER, SIR DAVID (1781–1868)
• BREWSTER, WILLIAM (c. 1566–1644)

Brewster and other physicists and mineralogists and it only remained to apply their methods to the minerals visible in rock sections . Very rapid progress was made and the names of See also:

• ZIRKEL, FERDINAND (1838– )

Zirkel, See also:

• ALLPORT, SAMUEL (1816–1897)
• ALLPORT, SIR JAMES JOSEPH (1811-1892)

Allport, Vogelsang, Schuster, Rosenbusch, See also:

• BERTRAND, HENRI GRATIEN, COMTE (1773-1844)

Bertrand, See also:

• FOUQUE, FERDINAND ANDRE (1828-19o4)
• FOUQUE, FRIEDRICH HEINRICH KARL DE LA MOTTE, BARON (1777-1843)

Fouque and See also:

• LEVY (Fr. levee, from lever, Lat. levare, to lift, raise)
• LEVY, AMY (1861–1889)
• LEVY, AUGUSTE MICHEL (1844– )

Levy are among those of the most active pioneers in the new field of See also:

• RESEARCH (O. Fr. recerche, from recercher, re- and cercer, mod. chercher, to search; Late Lat. circare, to go round in a circle, to explore)

research . To such importance have microscopical methods attained that textbooks of petrology at the present 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 are very largely devoted to a description of the appearances presented by the minerals of rocks as studied in transparent micro-sections . A See also:

• GOOD, JOHN MASON (1764-1827)

good rock-section should be about one-thousandth of an inch in thickness, and is by no means very difficult to make . A thin Sections. splinter of the rock, about as large as a See also:

• HALFPENNY, WILLIAM

halfpenny may be taken; it should be as fresh as possible and free from obvious cracks . By grinding on a plate of planed See also:

• STEEL, FLORA ANNIE (1847– )

steel or See also:

• CAST (from the verb meaning " to throw "; the word is Scand. in origin, cf. Dan. kaste, and Swed. kasta; " cast " in Middle Eng. took the place of the A.S. weor pan, cf. Ger. werf en)

cast iron with a little fine See also:

• CARBORUNDUM

carborundum it is soon rendered See also:

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

flat on one See also:

• SIDE
• SIDE (mod. Eski Adalia)

side and is then transferred to a See also:

• SHEET

sheet of plate glass and smoothed with the very finest See also:

• EMERY (Ger. Smirgel)

emery till all minute pits and roughuesses are removed and the surface is a uniform plane . The rock-chip is then washed, and placed on a See also:

• COPPER (symbol Cu, atomic weight 63.1, H=1, or 63.6, O = 16)

copper or iron plate which is heated by a spirit or See also:

• GAS

gas See also:

• LAMP (from Gr. Xag ras, a torch, Xaµaav, to shine)

lamp . A microscopic glass slip is also warmed on this plate with a drop of viscous natural See also:

• CANADA

Canada See also:

• BALSAM (from Gr. f &X raµov, through Lat. balsamum, contracted by popular use to O. Fr. basme, mod. Fr. bdme; Eng. balm)

balsam on its surface . The more volatile ingredients of the balsam are dispelled by the heat, and when that is accomplished the smooth, dry, warm rock is pressed firmly into contact with the glass plate so that the film of balsam intervening may be as thin as possible and free from air-bubbles .

The preparation is allowed to cool and then the rock chip is again ground down as before, first with carborundum and, when it becomes transparent, with fine emery till the desired thickness is obtained . It is then cleaned, again heated with a little more balsam, and covered with a cover glass . The labour of grinding the first surface may be avoided by cutting off a smooth slice with an iron disk armed with crushed See also:

• DIAMOND

diamond See also:

• POWDER (through O. Fr. puldre, modern poudre, from Lat. pulvis, pulveris, dust)

powder . A second application of the slitter after the first See also:

• FACE (from Lat. fades, derived either from facere, to make, or from a root fa-, meaning " appear "; cf. Gr. cbatvstv)

face is smoothed and cemented to the glass will in See also:

• EXPERT (Lat. expertus, from experiri, to try)

expert hands leave a rock-section so thin as to be already transparent . In this way the preparation of a section may require only twenty minutes . The microscope employed is usually one which is provided with a rotating stage beneath which there is a polarizer, while above the Microscope. objective or the eyepiece an analyser is mounted; alter- natively the stage may be fixed and the polarizing and analysing prisms may be capable of simultaneous rotation by means of toothed wheels and a connecting-See also:

• ROD (O.E. rodd, probably related to Norw. rudda, stick, rodda, stake)
• ROD, EDOUARD (1857-1910)

rod . If ordinary light and not polarized light is desired, both prisms may be withdrawn from the axis of the See also:

• INSTRUMENT (Lat. instrumentum, from insincere, to build up, furnish, arrange, prepare)

instrument; if the polarizer only is inserted the light transmitted is plane polarized; with both prisms in position the slide is viewed between " crossed nicols." A microscopic rock-section in ordinary light if a suitable magnification (say 30) be employed is seen to consist of grains or crystals varying in colour, Characters See also:

• SIZE

size and shape . Some minerals are colourless and trans- See also:

• PARENT, SIMON NAPOLEON (1855– )

parent parent (quartz, calcite, felspar, muscovite, &c.), others are yellow 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 (rutile, tourmaline, biotite), green (See also:

• DIOPSIDE

diopside, hornblende, chlorite), blue (glaucophane), pink (See also:

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

garnet), &c . The same mineral may present a variety of colours, in the same or different rocks, and these colours may be arranged in zones parallel to the surfaces of the crystals . Thus tourmaline may be brown, yellow, pink, blue, green, See also:

• VIOLET

violet, grey or colourless, but every mineral has one or more characteristic, because most See also:

• COMMON

common tints . The shapes of the crystals determine in a general way the outlines of the sections of them presented on the slides . If the mineral has one or more good cleavages they will be indicated by systems of cracks (see Pl .

III.) . The refractive index is also clearly shown by the See also:

• APPEARANCE (from Lat. apparere, to appear)

appearance of the sections, which are rough, with well-defined See also:

• BORDERS, THE

borders if they have a much stronger refraction than the See also:

• MEDIUM

medium in which they are mounted . Some minerals decompose readily and become turbid and semi-transparent (e.g. felspar); others remain always perfectly fresh and clear (e.g. quartz), others yield characteristic secondary products (such as green chlorite after biotite) . The inclusions in the crystals are of great See also:

• INTEREST

interest; one mineral may enclose another, or may contain spaces occupied by glass, by fluids or by gases . Lastly the structure of the rock, that is to say, the relation of its components to one another, is usually clearly indicated, whether it Micro- be fragmental or massive; the presence of glassy matter structure. in contradistinction to a completely crystalline or holo-crystalline " condition; the nature and origin of organic fragments; banding, foliation or lamination; the pumiceous or porous structure of many lavas; these and many other characters, though often not visible in the hand specimens of a rock, arc rendered obvious by the examination of a microscopic section . Many refined methods of observation may be introduced, such as the measurement of the size of the elements of the rock by the help of micrometers; their relative proportions by means of a glass plate ruled in small squares; the angles between cleavages or faces seen in section by the use of the rotating graduated stage, and the estimation of the 326 the bars of which remain parallel to the wires in the field of the See also:

• EYE
• EYE (O. Eng. edge, Ger. Auge; derived from an Indo-European root also seen in Lat. oc-ulus, the organ of vision (q.v.)

eye-piece . Sections perpendicular to an optic axis of a biaxial mineral under the same conditions show a dark See also:

• BAR
• BAR (0. Fr. barre, Late Lat. barra, origin unknown)
• BAR, CONFEDERATION OF
• BAR, FRANCOIS DE (1538-1606)
• BAR, THE

bar which on rotation becomes curved to a hyperbolic shape . If the section is perpendicular to a " See also:

• BISECTRIX (fem. of Lat. bisector, from bi-, two, secare, to cut)

bisectrix " (see CRYSTALLOGRAPHY) a black cross is seen which on rotation opens out to form two hyperbolas, the apices of which are turned towards one another . The optic axes emerge at the apices of the hyperbolas and may be surrounded by coloured rings, though owing to the thinness of minerals in rock sections these are only seen when the double refraction of the mineral is strong . The distance between the axes as seen in the field of the microscope depends partly on the axial angle of the crystal and partly on the numerical See also:

• APERTURE (from Lat. aperire, to open)

aperture of the objective . If it is measured by means of an eye-piece See also:

• MICROMETER (from Gr. wcp6c, small, jArpov, a measure)

micrometer, the optic axial angle of the mineral can be found by a See also:

• SIMPLE

simple calculation . The quartz wedge, See also:

• QUARTER (through Fr. from Lat. quartarius, fourth part)

quarter mica plate or selenite plate permit the determination of the See also:

• POSITIVE (or PORTABLE) ORGAN

positive or negative See also:

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

character of the crystal by the changes in the colour or shape of the figures observed in the field .

These operations are precisely similar to those employed by the mineralogist in the examination of plates cut from crystals . It is sufficient to point out that the petrological microscope in its See also:

• MODERN

modern development is an optical instrument of great precision, enabling us to determine physical constants of crystallized substances as well as serving to produce magnified images like the ordinary microscope . A great variety of See also:

• ACCESSORY

accessory apparatus has been devised to See also:

• FIT

fit it for these special uses . The separation of the ingredients of a crushed rock powder from one to another in order to obtain pure samples suitable Separation for See also:

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

analysis is also extensively practised . It may ofcompo- be effected by means of a powerful electro-magnet nents. the strength of which can be regulated as desired . A weak magnetic field will attract magnetite, then haematite and other ores of iron . Silicates containing iron will follow in definite order and biotite, See also:

• ENSTATITE

enstatite, augite, hornblende, garnet and similar ferro-magnesian minerals may be successively abstracted; at last only the colourless, non-magnetic compounds, such as muscovite, calcite, quartz and felspar, will remain . Chemical methods also are useful . A weak acid will dissolve calcite from a crushed limestone, leaving only dolomite, silicates or quartz . Hydrofluoric acid will attack felspar before quartz, and if employed with great caution will dissolve these and any glassy material in a rock powder before dissolving augite or See also:

• HYPERSTHENE

hypersthene . Methods of separation by specific gravity have a still wider application . The simplest of these is levigation (Lat. levigare, to make smooth, See also:

• LEVIS (formerly Pointe Levi)

levis) or treatment by a current of water; it is extensively employed in the See also:

• MECHANICAL

mechanical analysis of soils and in the treatment of ores, but is not so successful with rocks, as their components do not as a rule differ very greatly in specific gravity .

Fluids are used which do not attack the majority of the rock-making minerals and at the same time have a high specific gravity . Solutions of See also:

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

potassium mercuric iodide (sp. gr . 3•i96), See also:

• CADMIUM (symbol Cd, atomic weight 112.4 (0=16))