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1. ROCKS* The eorth's crust is composed of rocks.,{ Rocks ore composed of minrqls

A) ROCK AAINERAL5;il" A minerql is composed of qn ordered orroy of otoms chemicolly bondedtogelher to form o porticulor crystolline structure. This orderly stocking ofotoms is reflected in the regulqrly shoped objects colled crystols.'* Eoch ninerol hos o definite chemicol composition which gives il o unique sefof physicol properties.+ The elements of the eorth's crust qre orgonized into cornpounds ihot orerecogntzed os minerols. In other words, minerols ore conposed of theditferenl elements of the Eorth."1" only 8 elemehts compose the bulk of these minerols ond these elementsrepresent over 987" (by weight) of the continentol crusf.* These 8 most obundont elements of the Eorth's crust ore oxygen, silicon,

oluminum, iroh, cqlcium, sodium, potossium, ond mqghesiun.

i) Physicol Proprties of MinerolsThe more eosily recoqnized physicol properties of mingrqls include:

'i! Crystol form: the externql expression of o minerol thqt reflects lhe orderlyinternol orrongemeht of dtoms;+ Lusteri the oppeoronce or quqlity of light reflected frotn the surfoce of o

minerol;{ Colou produced by the presence of impurities in the minerol;'f Streokr the colour of o minerol iti its powdered\form ond is obtoined byrubbing the minerol ocross o piece of unglazed porceloin:

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nl Hordness: d meosure of lhe resistqnce of o minerol to obrosion orscrqtching. Mohs Scole of Hordness is the bosic comporison tesi;

J Cleovoget ihe iendency of o minerol to breok qlong Plones of weok bonding.It is the direction of splittjng in metomorphic rocks, orising from thepdrollel olignnent of plqty minerols such os mico;

+ Froclurei minerols thot do no exhibit cleovoge when broken, such os quortz,ore soid 10 froc-ture - those thot breok into smooth curved surfocesresernbling broken gloss hqve o conchoidol froclure; others breok iniospliniers or fibres, but most minerols frocture irregulqrly;*l Specific grovityr o number representing the roiio of the weight of o minerolto the weight of on equol volume of woier.& To dqte.4OO0 minerols hqve been identified - only o few dozen moke uP mostof ihe rocks of the eorth's crusf ond ore clossified os ihe rock-formihg

minerols.

ii) The Rock-forming Minerols+ 9 groups of rock-forming minerols:

i. the Elements groupii. the Sulfides groupiii the Hdlidesiv. the Oxidesv. the Corbonqtesvi. the Sulphqiesvii. ihe Phosphqtesviii. ihe Silicqtesix. Orgonics

B) TyPES OF ROCKS* Rock: ony oggregote of minerols in o solid stofe. \* Comes in o wide ronge of conPosifions, physicol chdrocteristics qnd oges* Usuolly composed of 2 or more ninerols

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& Con be divided inio 3 clqsses bosed on how they form (lheir origin):. Igneous rocks. Sedimentory rocks. Metomorphic rock

i) Igneous Rocks"l Forms when mogmo cools ond solidifies.+ The type of igneous rock fhot forms from mogmo dePends oh 3 fociors:

1. The chenicol cornposition of the mogmo;2. Temperoture of solidificotion;3. The rote of cooling1. Chenicdl conposition of the magma

'* 4 bosic types of mogmo occording to fheir chemicol composilion4. Felsic nogmos: contoin high quontities of sodiun, dluminum, potossium ond >65% salico. Rocks forned from felsic mogmos include gronile, diotite, dociteqnd rhyolite.+ All these rocks ore light in colour because of the doninonce of guotlz,potossium ond sodium feldspors ond plogioclqse feldspor minerolsn! iliofic nognosl rich in colcium. iron ond nognesium but ore relatively poor insilicq (45 - 52%). They produce rocks with o qimilor chemicol composilion.fnclude fine-groined bosolt (extrusive igneous rock/volconic rock) ond

coorse-grained gobbro (the intrusive'iwin" of bosolt). Mqfic igneous rocksiend to be dork in colour becouse they contoin o lorge Proportion of minerolsrich rn iron dnd mognesium.

,lL Irtermedidte mogmosi hqve q chemicol comPosition between felsic ond mofic(silicq between 53 - 65%). Rocks cooled frorn intermediote mogmos ore richin plogioclose felspqr. qmphibole ond pyroxene. Includes the rocks qndesite(o common volconic rock) ond diorite. \

,& Ultromofic nogmds: low omounls of silico (< 45%) ond ore dominoted by theminerqls olivine, colcium-rich plogioclose feldspors ond pyroxene. Peridotifeis the nost comrnon ultrqmqfic rock. Exfremely rote at the eorth's surfqce.

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Z. femperdture of solidificalion'il Rocks thot begin their cooling ot low temperotures (neor the eqrih'ssurfoce) tend to be rich in minerqls conposed of silicq, potossium dnd

oluminum.

"l Rocks thot begin theit cooling ot higher temperotures (thqt is, qt greqterdepths below the earth's surfoce) ore dominoted by minerols rich in colcium,sodium, iron ond mognesium.

3. Pale of cooling*. Role of cooling is importont in crystql development. It deternines thetexture or size of crystdls.lL Igneous rocks thot form through o groduol cooling process tend to hovelorge crystols. Relotively fost cooling of mogrno produces smoll crystols.i! Volconic mogmo thof cools very quickly on the eorth's surfoce produceobsidion (volconic Aldss), which contoins no crystolline structures.

ii) Sedimentory Rocks

+ Are layeted occumulotions of minerol porticles (sediments) derived in voriouswoys from pre-existing rocks (which could be igneous or netdmorphic).'{ fnvolves the wesfhering of pre-existing rock, lronsportolion of thewealhered moteriql frorn fhe originql site, onC deposition of the erodedmoteriol in the seo or in sone oiher sedimentqry environment.+ The deposited sediments then undergo liihificotion to become sedimentoryrocks.+ Lithificotion refe$ to the process thqt turns row rock sedimenl inlo

consolidqfed sedimenfqry rock.If con occur by woy of:. Drying ond conpoction. Oxidotion of iron ond oluminum. Cementolion of loose sediments by colcium ond silicq minerdls

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Dislinguishing fealures of sedinentary rocks.1. Occur in distinct loyers which ore differcntioted by colour, texture,

composiiion, etc. fhese loyers ore terned siroto or beds. The plonesseporoting the loyers ore plones of strotificotion or bedding plones.

{ Groded beddihg: A progressive decreose in gtain size upword through thebed. Commonly produced on the deep ocean floor by turbidity currentswhere os the currents move, their velocity groduolly decreoses so fhot thecoorser porticles qre deposited first.& Cross-bedding: An orrongement of smoll beds lying ot on ongle to the moinsedimenlory loyer.+ Contoin onimol ond plont fossils.

Mud crockGroded 5edding

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Classificalion of sedinentdry rocks* Can be categotized into 3 groups bosed on sedimeni type into:. Clostic sedimeniory rocks. Chemicol sedimentory rocks. Orgonic sedrmenfory rocks

. Ctasfic sedimentary rocks,$ Formed either from the frogrnents of other rocks or from lhe breok up onddeposition of shells. corol ond other morine orgonisms. Exomples qre thenoteridls in a sond bor of o river bed, or on o sondy oceqn beoch.

Nome of rock Froqmnt tvDeBteccioConglomero'feSondstoneArkose5holeSilfstoneMudstoneLinestone

Coorse frqgnents of ongulor grovel ondrockCoqrse frqgments of rounded grovel ondrockSond-sized porticles thof ore 90% quarlzSondstone composed of 25% feldspor grainsCloy porticles5ilt porticlesMixiure of cloy ond siltMixture of shells, corol ahd other morineskeletohs. Chenical sedimentary rocks

iL Formed by direct precipitqtion of minerqls fiqm solution. These minerolsinclude Co, No, K, ond M9. fn the process of chemicol precipitotion, ions insolution combine to form solid minerol motter seporqte from lhe solutions.An exomple is o loyer of rock solt, such os thot found in dry loke birds in oridregions.

Nome of rock PreciDitqte iypeHolite6ypsumSilcretesFefficretesLimestoneDolomite

Sodiutn ond chlorineColcium, sulphur and oxygenSilico \IronCdlcium corbonoteColciun, mognesium. corbonote

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. Orgdnic sedinentary rocks+ Consists of the lithified remoins of plonts ond onimols; the tissues of plonis

ond onirnols occunuloted ond preserved afler lhe deolh of the orgonism. Anexqmple is o layet of peat in o bog or morsh.

Nome of rock PreciDitote tYDeChetlCool

Rehqihs of tiny morine orgonisms thot noketheir skeletons of silicoLithif ied Dloni rernoins

iii) Metomorphic rocks;! Rock thqt have been oliered by heot, pr*sure ond the chemicol oction ofpore fluids to such on extent thqt the disiinguishing feotures of the originolrocks ore modified or erosed.d Con be formed from igneous, sedimentory or even previously metomorphosed

rocks.'[ Like igneous rock, hove o crystolline Structure, i.e. interlocking crystols,usuolly with o preferred groin orientqfion.,{ During metonorphism, new minerols, new textures dnd new Siructures

develop.+ Constitute o lorge port of the continentol crust.+ Provide evidence thqt the eqrth's crust hos bBen subjected to tepeoleddeformotion throughout geologic time, suggesting thoi the fectonic system

hos operqted during most of ecrth's history

DistitguithitE feolures of netanorihic rocks2 mojor groups:

l. rocks lhol possess o detinite plonor textur or folioted rocks:2. rocks ihot lock foliotion ond hove a gronulor texture or non-folidled rocks

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1. Folidled rocks* During metornorphism. minerolgrqins in rocks odjusi ond re-crystollize.+ New minerdls gtow in the direciion of leost stress so rocks ore produced in

which minerol grains hove o strong preferred orientotion.'t This gives rock o distincfly plonor elemeni cqlled foliotion.+ E.9. sldte, schist ond gneiss

lmaqeA lmage aFigure 2. Rocks minerols re-or|'onge in the direction of ldst stress to give fhenetomorphosed rock o Plonor texture

2. Non-foliated rocks"! Rocks originolly composed of one minerol (such os limestone ond sondstone),which forrns equi-dimensiondl crystols, do no develop sfrong folioiion.+ Insteod, they develop q gronulor texture with lorge minerol groins..! E.9. when o fine-groined linestone is metomorphosed, lhe smoll colcitecrysfols combine to f ormlorge, interlocking crystols, resuhing in o rock with

o texture similor to thot of o coorse-groined gronite."! E.9. include morble (formed from limestone) ond quortzite ( o very hordmetomorphosed rock formed from guortz sondstone\

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Exornples of mefomorphic rocksRock DescriDtion /tidior minerols Oriqinol rock

Morble

Quortzife

6heass

Schrst

slote

Non-folioted.coorse-groinedNoh-folioled.coorse-groandFolioled, nediun+o coorse-groanedFolio+ed, coorse-groined, loyered,floky or plotytexlureFolioted, ve.y fine-groihed. splatscledhly on flof,porollelcleovogeblones

Cdl.ile

QlortzFlspors, quorlz,micog

Qudrtz, lnicos

Cloy minerols

Limesfohe,dolomitSqndstone

Gtonile

Vorious sholes

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c) THE ROCK CyCLE

{ The rock cycle is o generol model thot describes how vorious geologicolprocesses creote, modify, ond influence rocks.This model suggests thol the origin of oll rocks cqn be ultimotely trocedbqck to ihe solidificotion of nol.ien mogmd.Igneous rocks form from the cooling ond crystollizofion of nqgmo os itrnigrotes closer to the Eorfh's surfoce.ff the crystollizdtion process occurs ot the Eorth's surfoce, lhe rockscreoted ore called extrusive igneous rocks.

Irtrusive igneous rocks ore rocks thdt fo"m \"ithin fhe Edrth's solidlifhosphere. fntrusive igheous rocks con be brought to the surioce of theEoflth by denudotion ond by o vqriefy of tectonic processes.

5e{:lment-*---!-Erosior, Trdnsportand 0eposiHonSurlal andtithificatlon

Melting MeltirgSUsSURFACE ENVIfi ONMENT

1II6H PBESSURE AND IEMPERATUFS

Vovrnent ofMagmdlo aath s Sul.fdce

Met!mffphlsm Metdmorphlsm

Figure 3. The Rock Cycle

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'S lgneous rock undergoes weofhering to form sediment. The sediment istransported ond deposited in ploces such os obeoch or in o delto, or in ihedeep sea etc.

il The deposited sediment undergoes lithificdtion (the processes thot turn itinto o rock). This includes the processes of cEmentotion ond compoction.

+ As the sedimentory rock is buried under more ond more sediment, the heoiond pressure of buridl cquses netomorphistn fo occur. This transforms thesedimentory rock into a netomorphic rock.+ As the metomorphic rock is buried more deeply (or os it is squeezed by plqte

tectonic pressures), temperotures qnd pressures continue to rise. If thelemperoture becones hot enough, the metomorphic rock undergoes melting.The molten rock is colled tnogmo. This completes the cycle.

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Char eclcrfetr?s of R ack

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56 nLcoll r H,sotts ANo IANDI-oRMsqpJtheflngan,I'"rr.\rtr.lomrto\.wo,L\.ror.l rori.\.rndLrorr Rurrncgutd,*e,th.r'ng at.o o.. , s on Jpprr.nrty unitornt jrnds(one.w ilh morc clay or feldspars, sandsloncs be.ome 8 re)*,ckcs o. a rkoses .nrcsc h avcutany propc.lis in common wi1h sandstooas; most ofthe ditferences are axributableio grealer ease ofchenical wcirhering

S/'dler. Sh'hL\rhec.mnr.n \trukexpordarrtrcrJrthirudrr,burNtifll-..rrrd,ed,p-'hdps be.ru\. ir usualty ro[ns towtdnd\ and N trl|te c\pos..l Sr,,r..."^;., oi.lay nrneral5 w,rh m'cn an,l o..aiondtort,e, minc, ats, or,co qrh a higt, .he;.; ;i;;.;ra_(ion Carbonarc is prescnt h marls. Bcddins is usua y*clr mirk"cd. \i"rii;;; Loften intense ar rhc surface and decreascs down tfr" p-fir", rrur p.oi.r. ,rong.r;ik.to a much grearcr deprh. Thls rhc rock is broken inio biocks wriich ar. r.*r".-rta.,but wearhered on thcir faccs. In the cnse of marts rhere is dccalcificarion from tircsurface, following fissures, wirh the accumula(ion ofan insolubrc residue "r th. "";;"_hedip ofnrara "ffecls wearhe ring. In horizontalshale rt is hard for wa,_.-;;Lil:: b,, ,, ,n: sr,drn lrlc recpty,nctin.r n,rny bed,tins ptaner a,c erpo\ed. $hi.hailows ea\y wrrer penerrarionShales erode faster than nosr se{tjmnhryroct s, nol only because thcy are sofr arr.twrJ'h' mo'e..-'sity. bur b.cause rhey a,e impem,.jbh and so rh.re is "i",';i ,,;o,r. r nere r\, rn.'etor(.. a grcrl(, tcnd.n^ ior rhe *"arher"d proJrt.l ro be r.movi l11:.:':-,,,,.",'.,,". i,.tu,ri,18Joromirp.^di.rrnrui\her bv . mrrhrrrar_r soruhrr,r\ thn,r! hp,.um,n^n'o.I\Fr,."pr re\rr.me.trnr,rrcn\i,oUnre,lr,,soturr.,ni.In. prrJo, rndn' s.ilhp ng aB"nr uf t,m".rorr. Tt," a, ruJi p,o"F* ot w.rrh.UnrdFt.nd\ on rh. vir rFry ot trmesr,,n.. Sumc i\,jen." -","."",,i.r,.,"i._;;,;;;;.nd :olulon r . un..'r'rir"d dtons iourrs dnd trddrnx plal"\ t1,,, is rl,. *,r'; ;;".\ro,, rl,d.rur-s.,iprortuprd,,r'ropog,rph)O,h-;jin-,,or",r,.m,:_.,,..i;,'l,rlr.d d,l,rn( I',r...ro,'. wJr.r p.,r.r,arp\rt,.Fnri,,,,rt tstr,"",,.1,..,,,,..,""._,,k, drh.,rng...,,lr jo,,r,\ dnd t, ddUrS ptJn,.. Jr. or tr t. o, no,,,ip.,un,. r,1..,, o,'., o Jrr vurLondre,'1dv to,m,r o, n. .r rh" \ufl .,,.,,t so t,n "!;,r,.\ roln,ne, l.Jrilaycr known as .:aLE1c, .otol," .na .rn", n,.,.,Igu:ou rorkIgn"ou\ ,o, I s may b. a/tuvrp rhir ,\. e,ujrrcd ar ttrc.Jrih.\ \uriac. -a tr\r fluw\ o,ds voi Jnr. dsll \how. r\t htpobv{at, Iltdt 6. emptr. ed as JytFs \rfl , or orhe, f..,Jr.s inlr'.,L,ppcr ldlcr\ot rireeJflh..rurt.orp/lroarr.rha,i, rornrc,iarcon\idp,Jhl.dpprtrrn rhe canLs.,,^r, I L, 'e.rl .e lrnds or rgnFous ro ! -rupr^.. trprbysdt dnd fjuro,rr a,e .o ,ldr'al wirh the tsrrin :r/c olrh^ rl} k miI.r Jt, lrurrw" ro

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58 nEcoLITH, sotls AND LANDI-ORMSprotile in suitablc .nvi'onnrc.(s 'Floare.s' of unwearhcred Msak occasio!r:r v o.orrin,l"yBasaltic volcrnic ash, bcing porous, gener:r ywealhrs rapidly, fonning fe(itc soilsin a rclalively short time. -nre fullcr\ earrh of the Mcsozoic of sourhem Eogland isweathered volcanic ash and is almosr pure c?tciun montmoritlonirc. tl;rc is aspcclacular increasc in lhe 2mount of montmorillonitc ir the Crelaceous ofEngland,whi, h may b. rcla{cd lo rn. rcd\rne trorrgh dr\lJn') \ ol.an,. a.tiviryDol..r'rr- Dolerire (knovn as'di?base'in rhc USA) haslhe samechenlicat and mnreralo8ical composnion as baiak, ard wcalhers in a slmilar way, Joiniing is lvc ma,kedand.egular,/th]olrre. Rhyolirc isan ac;d effusive igncous iock tliar conrains quarlzand so can givense Iosand upon wearherinS- It ;s not so wilhcrabte as basalt, and gives rise rosial-Iowcr ard poore r soils A frorhy, gtrsst va riery of rhyoli(c is ca [ed .pumice,- I I wealhers

.slowly and foms lroor sandy soits.,rnd6rrd, Andcsiie is an cffusivc ignous rock ot inlermediare composrrion, wj(hwea(hering properties inrermediate between basall anit ihyotile.MetaDlotphic rockMclxmorphrc rocks arcrrcircd byrtrer.tion ofprc exisrnrS rocks, whct her l8ncous orsedincnri.y, by heat, pressurc or Lrolh A.oundlhccdgesofagranircpturonrhercrsusually a rirg or'aureole'ofmct?mor?hism rhar convcrls thc counrry.ock inro hornlls, usually a fnrc grained, vcry rougtr rockMosl mclamorphjc rocks are distioguishcd by a very merked prefered o.ientariorot mrner.ls, thc dcvelopmcnr of new nrincr?ls ar thc expe se ofor;ginal oncs, ard lhclornrxtion o{ a very markcd fissilit} nr many prra et parr;nss, described as .staritress,"! ,i,i\ro-r) aoJrs. Briin".t rr't1mo,ptr'. ro,t\",ccr c.l8a.a\,anJliner.A,JtD.d,,n.\lv t,.. \lar" and !./r/\/ tlo I rJn{ m;.prJl\trv, rrcr^LIijin.rvJn.|l... u,hr..,rtica s.hisi, ardaluiite sltaic, ctc , and zoncs ofdifferenl degrecsofmetarnorphism ?recharaclcrized bydiffercDr mincralissemblages. Veryfinc grained rocks may bc mctnmolPho:icd to slale Ma.ble i5 mctamorptroscd tinresloncG,r.rr. Cneiss is a coarse grained, foliared rock co.taining quaI1z, fcldspn,, anrphi-bolcr, pyroxcncs, mica.nd garner- It is inlermediatc in propcrties berweenAranitc;nds.hFr lr i\ r Jr.lv as welltornred and unrtor mly massive as gr iniL". MrrFrrti Jr scgrc8aled nno laycrs, and bands of lh most wealhclabte mineral affecr ihe rotal rockslrcn8lh a property that oflen provcs trolrbtesome ;n engineerinB_&r.i. Schistconsiisofthi laycrsoidiffcrcnl,ninerals,Ihe.schistosiry'.Irsptirsveryeasily aloog bands of mic-?, and this is ve.y imporranr i. lvarherin8 Schisri conrainsomc very resistant minerals but wealhering is modcratejy east Froslweaiherinp canrrp ly break upschist-LIatble. Marble is meramorphosed timesrone, and ir wenthers in a nrajor rcspecrslikc a dense lime

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N'IINFR AI- AND ROCK \I'EATHERINCJO@rrz!r.. Mclamo.phoscd sandstonc is known asquarrzllc Th;shas lostlhe porosilyot sandslone, so

'seven less wc?{hcrablc Ir i5 almosl ined chctnically, a'd Ph}sical

wealhering 's dominant I})e m(xt ancient erosion surfaces are ofien PreseNed onquadzite, the mosl.esislant rock ofallAnphtbolilt Amphibolite consists alrnost entirelyof homblelrde- It weathcrs ratherlike basalt, oftenvery decply, gMnS rl5c lo a claywith abundaDt ba-res aJ)d iron- Cleavagecnables casf wlllerpeDeiralioo and deep wcalhcnngSldrz- State is r fine-grained mclamoryhic rock lhal splils inlo vcry thin plates.Cle?vagc planes sepa.atinglhe pliles oflen cul across layedngin lhc oriSinal rockPlry i/.- I'hyllite rpresenls a highcr sDgc of rnetamorphism than slxtc It is hiShlylusrrous bccause o(rhe highconlenl of mica, ahhouSh the mica grains can bc seen onlyu dera microscopc Some phylliles have eisible crystals ofgarnel and olher mincmlsrtr ialtu., ? oJ rc, L :ttu.tu.Ro.t srnl. tur"\ md] he origin.l edntrenrdty o' 'gn".,rt l""ru'e., rh.v -iy be du. loahcralion Mrhi'r rhe rock, or they may rcsult frojn slresses applicd from otternalBa.ldir{ pkrnes. Ded