002_kegy205.docx

8/19/2019 002_kegy205.docx

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LANDFORMS

This unit deals with

Rocks and minerals — major types o rocks and their

characteristics

Landorms and their e!olution

"eomorphic processes — weatherin#$ mass wastin#$ erosion

and deposition% soils —ormation

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C H A P T E R

he earth is composed of various

kinds of elements. These elements are

in solid form in the outer layer of the

earth and

Tin hot and molten form in the interior.

About 9 per cent of the total crust of the

ear th i s composed o f e i!h t e lemen ts l ike

o"y!en# silicon# aluminium# iron# calcium#

sodium# potassium and ma!nesium $Table %.&'#

a n d t h e r e s t i s c o n s t i t u t e d b y t i t a n i u m#

hydro!en# phosphorous# man!anese# sulphur#

carbon# nickel and other elements.

Table 5.1 : The Major Elements of the Earth's

SL No. Elements By Weight(%)

(

)

r i * + c s i , - . . +

/"y!en *+.+

0ilicon 12.21Alumink # .&34ron %.Calcium 3.+3

0odium 1.3Potassium 1.%9

5a!nesium 1.9

/thers &.*&

The elements in the earth6s crust are rarely

found e"clusively but are usually combined 7ith

other elements to make various substances.

These substances are reco!nised as minerals.

Thus# a mineral is a naturally occurrin!

or!anic and inor!anic substance# havin!

an orderly atomic structure and a definite

c h em i c al c o mp o si t io n a n d p h ys i c al properties. A mineral is composed of t7o

or more elements. 8ut# sometimes sin!le

element minerals l ike sulphur# copper#

silver# !old# !raphite etc. are found.

Thou!h the number of elements makin!

u p t h e l i t h o s p h e re a r e l i mi t e d t h e y a r e

combined in many different 7ays to make up

many varieties of minerals. There are at least

1# minerals that have been named and

identified in the earth crust) but almost all the

commonly occurrin! ones are related to si"

maor mineral !roups that are kno7n as maor rock formin! minerals.

The basic source of all minerals is the hot

ma!ma in the in ter ior of the earth . :hen

ma!ma cools# crystals of minerals appear and

a systematic series of minerals are formed in

se;uence to so l id i fy so as to form rocks .

5inerals such as coal# petroleum and natural

!as are or!anic substances found in solid#

li;uid and !aseous forms respectively.

A brief information about some important

minerals in terms of their nature and physicalcharacteristics is !iven belo7 -

MINERALS AND ROCS

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!"#SICAL C"ARACTERISTICS

$ i' E " te rn al c ry st al f or m ( d et er <

mined by internal arran!ement of the

molecu l es ( cubes# oct ahedrons#

he"a!onal prisms# etc.

$ ii ' Cl e av a !e ( t en d en c y t o b r ea k i n

! i ve n d i r ec t i on s p ro du c i n!

relat ively plane surfaces ( result of

in te rna l a r ran!emen t of t he

molecules ( may cleave in one or more

di rec tions and a t any an!le to eachother.

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$ i i i '@ rac tu re ( in t e rna l mo lecu l a r

arran!ement so comple" there areno planes of molecules) the crystal7ill break in an irre!ular manner#

not alon! planes of cleava!e.

$iv'=ustre ( appearance of a material7 i t ho u t r e !a r d t o c o l ou r ) e a c hmineral has a distinctive lustre like

metallic# silky# !lossy etc.

$ v ' Co l o ur ( s o me m i n er a ls h a vecharacterist ic colour determined

by thei r molecular s t ructure (

malachite# aurite# chalcopyrite etc.#and some minerals are coloured by

impuri t ies. @or e"ample# becauseof impurities ;uart may be 7hite#!reen# red# yello7 etc.

$vi'0treak ( colour of the !round po7der

of any minera l . 4 t may be of thesame colour as the mineral or maydiffer ( malachite is !reen and !ives

!reen streak# fluorite is purple or !reen but !ives a 7hite streak.

$vii' Transparency ( transparent- li!ht

rays pass throu!h so that obectscan be seen p la in ly ) t rans lucent ( li!ht rays pass throu!h but 7i ll

!et diffused so that obects cannot be seen) opa;ue ( li!ht 7ill not passat all.

$vi i i ' 0tructure ( part icular

a rr an !e m en t o f t he i nd iv id ua lcrysta l s ) f ine # medium or coarse! ra in ed ) f ib ro us ( s ep ar ab le #

diver!ent# radiatin!.$ i " ' Hardness ( re l at i ve r e s i s tance

be in ! sc ra tc he d) ten mi ne ra ls ar e

selected to measure the de!ree of h a r d n e s s f r o m & < & . T h e y a r e -

& . t a l c ) 1 . ! y p s u m ) 3 . c a l c i t e )*. fluorite) %. apatite) +. feldspar)2. ;uart) . topa) 9. corundum)&. diamond. Compared to this for

e"ample # a f in!ernai l i s 1 .% and!lass or knife blade is %.%.

$"'0pecific !ravity ( the ratio bet7eenthe 7ei!ht of a ! iven obec t and

the 7ei!ht of an e;ual volume of 7ater) obect 7ei!hed in air andthen 7ei!hed in 7ater and divide

7ei!ht in air by the difference of the

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SOME MA$OR MINERALS AND T"EIR C"ARACTERISTICS

%el&sar

S(l()on an& o*+,en are )ommon elements (n all t+es of fel&sar an& so&(-m otass(-m)al)(-m al-m(n(-m et). are fo-n& (n se)(f() fel&sar /ar(et+. "alf of the earth's )r-st (s)omose& of fel&sar. It has li!ht )ream to salmon (n0 )olo-r. It (s -se& (n )eram()s an& ,lassma0(n,.

-art2

It (s one of the most (mortant )omonents of san& an& ,ran(te. It )ons(sts of s(l()a. It (s a har&m(neral /(rt-all+ (nsol-ble (n 3ater. It (s 3h(te or )olo-rless an& -se& (n ra&(o an& ra&ar. It (s one of the most (mortant )omonents of ,ran(te.

!+ro*ene

!+ro*ene )ons(s ts of )al)( -m al-m( n-m ma,nes(-m (ron an& s(l()a. !+ro*ene forms 14 er)ent of the earth's )r-st. It (s )ommonl+ fo-n& (n meteor(tes. It (s (n ,reen or bla)0 )olo-r.

Amh(bole

Al-m(n(-m )al)(-m s(l()a (ron ma,nes(-m are the major elements of amh(boles. The+ form er )ent of the earth's )r-st. It (s (n ,reen or bla)0 )olo-r an& (s -se& (n asbestos (n&-str+."ornblen&e ( s anot her form o f amh(boles.

M()a

It )o mr( se s of o ta ss (- m al -m(n (- m ma,nes(-m (ron s(l()a et). It forms 6 er )ent of theearth's )r-st. It (s )ommonl+ fo-n& (n (,neo-s an& metamorh() ro)0s. It (s -se& (n ele)tr()al(nstr-ments.

Ol(/(ne

Ma,nes(-m (ron an& s(l()a are major elements

of ol(/(ne. It (s -se& (n je3elle(+. It (s -s-all+ a

,reen(sh )r+stal often fo-n& (n basalt() ro)0s.7es(&es these ma(n m(nerals other m(nerals l(0e )hlor(te )al)(te ma,net(te haemat(te ba-*(te

an& bar(te are also resent (n some 8-ant(t(es (n the ro)0s.

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@B,>A5E,TA=0 /@ PH04CA= DE/DRAPH

Metall() M(nerals

These minerals

contain metal content

and can be sub<divided into three

types-

(i)Precious

metals : !old#

silver#

platinum etc.

(ii)Ferrous

metals : iron

and other

metals often

mi"ed 7ith

iron to formvarious kinds

of steel.

(iii) Non-

ferrous

metals :include

metals like

copper# lead#

inc# tin#

aluminium

etc.

Non9Metall()M(nerals

These minerals do not

contain metal content.

0ulphur# phosphates

and nitrates are

e"amples of non<

metal lic minerals.

Cement is a mi"ture

of non<metallic

minerals.

ROCS

The earth 6s crus t i s

composed of rocks .

A rock is an a!!re!ate

of one or more

minerals. Rock may

be hard or sof t and

i n v ar i ed colours.

@or e"ample# !ranite

is hard# soapstone is

soft. Dabbro is black

and ;uartite can be

milky 7hi te . Rocks

do not have

defin i te

c o mp o s it io n o f

m i n e r a l

c o n s t i t u e n t s .

@eldspar and ;uart

are the most

common minerals

found in rocks.

Petrolo!y is

science of rocks.

A petrolo!ist

s tudi e s rocks

in all their

a sp ec ts v i .#

mineral

composition#

te"ture#

structure#

o r i ! i n #

o c c u r r e n c e #

a l t e r a t i o n

a n d

relationship7ith other

rocks.

As there is a close

relation bet7een

rocks and landforms#

rocks and soi ls# a

!eo!rapher re;uires

bas ic kno7led!e of

rocks. There are

many di fferent

kinds of rocks7 h ic h a r e !rouped

under three families

on the basis of their

mode of formation.

They are- $i' 4!neous

Rocks ( solid i fied

from ma!ma and

lava) $ i i '

0ed imen ta ry Rocks

*1

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( the re sul t of

deposition of

fra!ments of rocks by

e"o!enous processes)

$iii' 5etamorphic

Rocks ( formed out of

e"istin! rocks

under!oin!

recrystallisation.

I,neo-s Ro)0s

As i!neous rocks form

out of ma!ma and lava

from the interior of

the ear th# they are

kno7n as primary

rocks . The i!neous

rocks $4!nis <in =atin

means @ire6' are

formed 7hen ma!ma

cools and solidifies.

ou already kno7

7hat ma ! ma i s .

: h e n m a ! m a i n i t s

u p7a rd movementcools and turns into

solid form it is called

i!neous rock. The

process of coolin! and

soli dif ic ati on can

happen in the earth6s

crust or on the surface

of the earth.

4!neous r ocks

are c lass if ied based

o n t e " tu re. Te" t ure

d e pe n ds u po n s i ea n d a r ra n !e men t o f

!rains or other

phys ical condit ions

of the materia ls. 4 f

molten material is

cooled slo7ly at !reat

depths# mineral !rains

may be very l ar!e .

0udden coo lin! $at

the surface' results in

small and smooth

!rains. 4ntermediate

conditions of coolin!

7ould result in

intermediate sies of

!r ai ns maki n! up

i!neous rocks.

Dranite# !abbro#

pe !mat it e# basalt #

volcanic breccia and

tuff are some of the

e"amples of i!neous

rocks.

Se&(mentar+ Ro)0s

The 7ord sedimentary6

is derived from the

=atin 7ord

sedimentum# 7hich

means settlin!. Rocks

$i!neous# sedimentary

and metamorphic' of

the earth6s surface are

e"posed to

denudational a!ents#

and a re b roken up

into various sies of

fra!ments. 0uch

fra!ments are

transported b y

d i f f e r e n t

e " o ! e n o u s

a ! e n c i e s a n d

deposi ted. These

deposits throu!hcompaction tu rn

i nt o r oc ks . T hi s

proc es s i s ca l l e d

l ithation . 4n many

sedimentary rocks#

the layers of deposits

retain their

character is tics even

after li thification.

Hence# 7e see a

number of layers of

varyin! thickness insedimentary rocks

like sandstone# shale

etc.

>ependin! upon the

mode of formation#

sedimentary rocks are

classified into three

maor !roups- $i'

mechanically formed

( sandstone#

con!lomerate#

limestone# shale# loessetc. are e"amples) $ii'

or!anically formed (

!eyserite# chalk#

limestone# coal etc.

are some e"amples)

$iii' chemically formed

( chert# limestone#

halite# potash etc. are

some e"amples.

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54,ERA=0 A,> R/C?0

Metamorh()

Ro)0s

The 7ord metamorphic

means 6chan!e of form6. These rocks

form under the action

of pressure# volume

and te mper atur e

$PFT' chan!es .

5etamorphism occurs

7hen rocks are forced

do7n to lo7er levels

by tectonic processes

or 7hen molten

ma!ma risin! throu!h

the crust comes incontact 7ith the

crustal rocks or the

u nd er l yi n! r oc ks

a re s ub ec te d to

!rea t amounts of

pressure by

ov er lyi n! r oc ks.

5etamorphism is a

process by 7hich

already consolidated

rocks under!o

recrystallisation and

reor!anisation of

materials 7ithin

ori!inal rocks.

5echanical

disruption and

reor!anisation of the

or i!ina l mi ne ra ls7ithin rocks due to

b r e a k i n ! a n d

c r u s h i n ! 7 i t h o u t

a n y appreciable

chemical chan!es is

called dynamic

me t a mo rp h i s m.

T he m at er ia ls o f

ro c ks chemical ly

al ter and

recrys tal l ise due to

thermal

metamorphism.

There are t7o types

of thermal

met amor phis m (

contact meta<

morphism and

re!ional

met amorph is m. 4n

contact

met a mo rp hi s m t he

rocks come in

contact 7ith hot

int rudi n! ma !maand lava and the rock

materials recrystallise

under hi!h

temperatures. Guite

often ne7 materials

form ou t o f ma!ma

or lava are added to

the rocks. 4n

re!ional

metamorphism#

rocks under!o

recrystallisation due todeformation caused by

t e c t o ni c s h e a r i n!

t o ! e t h e r 7 i t h

hi ! h temperature or

pressure or both. 4n

the process of

me ta mo rp hi sm i n

s ome roc ks ! ra in s

or minerals !et

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arran!ed in layers or

lines. 0uch an

ar ran!e ment of

mi ne ra l s o r ! r a in s

in metamorphic

rocks is cal led

fo l iat ion or

l ineation. 0ometimes

minerals or materials

of di ffe rent !roups

are arran!ed into

alternatin! thin tothick layers appearin!

in li!ht and dark

shades . 0uch a

st ructure in

me ta morp hi c rocks

is called banding and

rocks displa yin!

ba nd in! ar e ca ll ed

banded rocks. Types

of metamorphic

rocks depend upon

o ri ! in al rocks t hat

7ere sub ected tometamorphism.

5etamorphic rocks

are c lass if ied into

t7o maor !roups (

foliated rocks and non<

foliated rocks.

Dneissoid# !ranite#

syenite# slate# schist#

marble# ;uartite etc.

are some e"amples

of metamorphic

rocks.ROC C#CLE

Rocks do not remain

in their ori!inal form

for lon! but may

under!o

transformation. Rock

cycle is a continuous

process throu!h

7hich old rocks are

transformed into ne7

ones.

4!neous rocks are primary rocks and

other rocks

$ se di me nt ary a nd

metamorphic' form

from these primary

rocks. 4!neous rocks

can be chan!ed into

metamorphic rocks .

The f r a ! me n t s

d e r i v e d o u t o f

i ! n e o u s a n d

metamorphic rocks

form into

sedimentary

Weathering and

Erosion

%(, 5.1 : Ro)0 C+)le

rocks. 0edimentary

rocks themselves can

turn into f ra!ments

a nd t he f ra !men ts

can be a source for

formation of

sedimentary rocks. The

crustal rocks

$i!neous#

me ta mor ph ic a nd

sed imen ta ry' once

formed may be

ca rri ed do7n intothe mantle $interior

of the earth' throu!h

subduct ion process

$pa rts or 7hol e of

crustal plates !oin!

do7n under another

plate in ones of

plate conver!ence'

and the s a m e m e l t

d o 7 n d u e t o

i n c r e a s e i n

t e mp e ra t ure i n t hei nt er io r a nd t ur n

into mol t e n

ma ! ma # t he

o r i ! i n a l s o u rc e fo r

i!neous rocks $@i!ure

%. &'.

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** @B,>A5E,TA=0 /@ PH04CA= DE/DRAPH

: E ; E R C I S E S

&. 5ul t ip le choice ;ues t ions .

$i' :hich one of the follo7in! are the t7o main consti tuents of !ranite

$a' 4ron and n i ckel $c' 0ilica and aluminium

$b' 4ron and s i lver $d' 4ron /"ide and

po ta ss ium

$ii' :hich one of the follo7in! is the salient f eature of metamorphic rocks

$a ' C ha n !e a b l e $c' Crystalline

$ b ' G u i t e $d' @oliation

$iii' :hich one of the follo7in! is not a sin!le element mineral

$a'Dold $c' 5ica

$b ' 0i lve r $d' Draphite

$iv' :hich one of the follo7in! is the hardest mine ral

$a' Topa $c' Guart

$b ' >iamond $d' @eldspar

$v' :hich one of the follo7in! is not a sedimentar y rock

$a' Til l i te $c' 8reccia

$b ' 8o r a" $d' 5arble

1. Ans7er the fol lo7in! ;uest ions in about 3 7ords.

$ i ':hat do you mean by rocks ,ame the three maor c lasses of rocks .

$ i i ':hat i s an i!neous rock >escr ibe the method of format ion andcharacteristics of i!neous rock.

$iii':hat is meant by sedimentary rock >escribe the mode of formation ofsedimentary rock.

$ iv':hat relat ionship e"plained by rock cycle bet7een the maor type of rock

3. Ans7er the fol lo7in! ;uest ions in about &% 7ords.

$i'>efine the term 6mineral 6 and name the maor classes of minerals 7ith their phys ical characteristics.

$ii'>escribe the nature and mode of ori!in of the chief types of rock at theearth6s crust. Ho7 7ill you distin!uish them

$iii':hat are metamorphic rocks >escribe the types of metamorphic rock andho7 are they formed

!roje)t <or0

Collect different rock samples and try to reco!nise them from their physicalcharacteristics and identify their family.

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002_kegy205.docx

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