Engineering Geology for Civil Engineer Chapter 2.pdf

IT IS BEST NOTE

1. Engineering Geology for Civil Engineers
CEng 4309
BelayBirhanu(MSc.)
[email protected]
OfficeBlock520/12
Chapter2
Crystals, Minerals and Rocks

2. Recap
Chapter one
✓Geology and Branches of Geology
✓Origin and History of the Earth
✓Internal structure and composition of the Earth
✓Earth’s Continental Plate Movement
✓Rock Age Determination Techniques
✓Application of Engineering Geology
2

3. Learning Objective
After complete this chapter the student able to:-
•To understand the concept of mineral and rock
•To understand the different types of minerals and rocks
•To understand the engineering geology consideration of
rocks
3

4. Today Agenda
•Concept of Crystals
•Minerals, formation of minerals, properties of minerals
and types of minerals
4

5. Crystals, Minerals and Rocks
➢All Earth materials are composed of atomsbound together.
➢Mineralsare composed of atoms bonded together and are
the building blocks of rocks.
➢Rocksarecomposedofmineralsandtheyrecordvarious
geologicprocesses.
➢Mattercanexistinthreestates:-Liquid,Gasandsolid
•Solid:-solidmoleculescanbecrystallinesolidsandnon
crystallinesolids(Amorphous)
5

6. Non crystalline (Amorphous) Solid
➢Anysolidhavingrandominternalarrangementofits
constituentatomsandionswithnoexternalcrystal
structure. E.g.Graphite
Crystalline Solid:-
➢Anysolidhavingaregularinternalarrangementof
atoms,ionsinthreedimensionalarrayinaregularand
repeatingmanner.E.g.diamond
➢Graphiteanddiamondbotharemadeupofthesame
elementcarbon,butgraphiteisamorphous(thecarbon
atomsaredistributedrandomly)anddiamondiscrystalline
solid(theatomsarearrangedregularly)
6

7. What is crystal?
➢ACrystalisasolidpiecehavinghomogeneousphysical
andchemicalcomposition,externallyshapedby
symmetricallynaturalsmoothfaces.
➢Crystalhavehighlyorderedatomicarrangementwhich
meansthattheatomsinamineralarearrangedinan
orderedgeometricpattern.Thisorderedarrangementof
atomsiscalledacrystalstructure,andthusallmineralsare
crystals.
➢Eachmineralhasacrystalstructurethatwillalwaysbe
foundforthatmineral,i.e.everycrystalofquartzwillhave
thesameorderedinternalarrangementofatoms.
7

8. 8
To Geologists
➢Mineralsarenaturallyoccurringinorganicsolidthathas
specificchemicalcompositionandregularinternalcrystal
structure.
➢Therefore,mineralsare:
oNaturallyoccurring:foundinnatureorproducedby
geologicalprocess.
oInorganic:excludedtheorganicmaterthatmakeup
plantsandanimals.donotcontainhydrocarbonswith
carbon-hydrogenbondsandNotproducedbybiological
processes
What is Mineral ?

9. 9
oSolid:Neitherliquidnorgasareminerals
oHasspecific(definite)chemicalcomposition:amineral
haveuniquechemicalcompositionwithaspecific
(unique)chemicalformula
oHasregularinternalstructure:Arrangementof
atomsinregular,repeatingpatterns……with
disorderedarrangementsarenotminerals
What is Mineral ?

10. 10
Some remarks and exceptions to the definition of minerals
➢Mostofthemineralsarecompoundsoftwoor
moreelements,buttherearefewmineralssuchas,
Sulphur,diamond,Auwhicharemadeupofsingle
elements,calledNativeminerals
➢Hgisamineralbutnotsolid
➢Eventhoughcoalandpetroleumarenatural
occurringtheyarenotminerals,becausetheyare
organicinorigin

11. 11
How Minerals form?
➢Mineralsformvianaturalenvironmentalprocessesthat
causeatomstobondtogethertoformsolids.Theseinclude:
1)Precipitationfromsolution:Solutionsfromwhichminerals
precipitateinclude:
•Surfacewater&Groundwater
•Hydrothermalsolutions,whicharewarm,aqueoussolutions
thathavebeenheatedatdepthand/orbyproximitytoa
bodyofmagma.
2)Sublimationfromagas
➢Sublimationoccurswherevolcanicgasesareventedat
Earth’ssurfaceorwheregasphasesseparatefromsolution
inthesubsurface.
➢LavaflowsatthesurfacewhichformvolcanicandMagmabodiesin
thesubsurface,whichformplutonicmineralsandrocks.

12. 12
3)Solidstategrowth
➢Insolidstategrowth,newmineralcrystalsgrowfromthe
constituentsofpre-existingminerals.Thisisespecially
commonduringtheformationofmetamorphicmineralsand
rocks.
4)Solid–liquidorsolid–gasreactions
➢Insuchreactions,atomsareexchangedbetweenthesolid
mineralsandtheliquidorgasphasewithwhichtheyarein
contact,producinganewmineral.
➢Thesesolid–liquidorsolid–gasreactionsarecommonin
mineral-formingprocessesthatrangefromweathering
throughveinformationtometamorphism.

13. 13
Properties of Minerals
➢Theproperties(i.e.physical,chemicaloropticalproperties)of
mineralsarethetraitswhichareusedtoidentifyanddescriptionof
mineralspecies.
➢Thesetraitsincludecolor,streak,luster,density,hardness,
cleavage,fracture,tenacity,andcrystalhabit.
1. Color
2. Luster
3. Hardness
4. Crystal shape
5. Cleavage
6. Streak
7. Fracture
8. Transparency
9. Specific gravity and others
Physical properties of minerals

14. 14
➢Generally unreliablefor mineral identification
➢Often highly variable due to slight changes in mineral chemistry
➢Exotic colorations of certain minerals produce gemstones
➢Quartz (SiO
2) exhibits
a variety of colors
oSulfur-Yellow
oAzurite-Blue
oMalachite-Green
oCinnabar-Red
oChromite-Black
A) Color

15. 15
B) Streak
➢Color of a mineral in its powdered form
➢Streakis obtained on an unglazed porcelain plate

16. 16
▪Resistanceofamineral
totheabrasionor
scratching.
▪Allthemineralsare
comparedtoastandard
scalecalledtheMohs
scaleofhardness.
▪Moh’sscalerelatesthe
hardnessofmineralswith
somecommonobjects,such
asfingernails,copper
pennies,asteelknifeblade,
andglass.
C) Hardness

17. 17
✓External expression of a mineral’s internal structure
✓Often interrupted due to competition for space and rapid
loss of heat
Cubic crystals of
pyrite
D) Crystal Form

18. 18
E) Luster
➢Itisthequalityandintensityoflightreflectedfromthe
surfaceofaminerals(responsetolight).
➢Twomineralscanhavethesamecolorbutdifferentluster.
➢Lusterdependsonthecrystalstructureofminerals
➢Therearetwomajortypeofluster
Galena, metallic lusterOrthoclase, non metallic luster
1) Metallic Luster 2) Non-metallic Luster

19. 19
2.1.2 Types of minerals
A.Based on their economic importance
1.Economicminerals:thoseexploredfortheir
economicimportance
2.Rockformingminerals:constituentsofrocks.
B. Based on their origins
1.PrimaryMinerals:directlycrystallizefrom
coolingmagma
2.SecondaryMinerals:formedaftersedimentation
andmetamorphism

20. 20
C. Based on their importance to the naming of rocks
1.Essentialminerals:theirpresentorabsentisaffect
namingoftherocke.g.quartz,feldsparsforgranite
2.AccessoryMinerals(non-essential):theirpresentor
absencedon’taffectthenamingoftherocks.E.g.Zircon
ingranite.
D.Based on their chemical composition:
•Silicate,
•Native,
•Oxides, etc.

21. Summary
•Acrystalisasolidwhoseatomsarearrangedina"highly
ordered"repeatingpattern.
•Mineralsarenaturallyoccurringinorganicsolidthathasspecific
chemicalcompositionandregularinternalcrystalstructure.
•MineralsformvianaturalenvironmentalprocessesThese
include:-Precipitationfromsolution,Sublimationfromagas,
SolidstategrowthandSolid–liquidorsolid–gasreactions
•Propertiesofmineralsisusedtoidentifythemineralsandsome
Physicalpropertiesofmineralsinclude:-Color,Luster,Hardness,
Crystalshape,Streakandothers
•Mineralcanbeclassifiedbasedoneconomicimportance,origin,
andtheirimportancetothenamingofrocks
21

22. Thank you
22

23. Chemical Classification of Minerals (Groups of
Minerals
23
BelayBirhanu(MSc.)
[email protected]
OfficeBlock520/12
Chapter2
Crystals, Minerals and Rocks

24. Recap
✓What is crystal?
✓What minerals?
✓Formation of minerals and properties of minerals
✓Differenttypesofmineralsbasedoneconomicimportance,
origin,andtheirimportancetothenamingofrocks
24

25. Today Agenda
•Chemical Classification of Minerals (Groups of Minerals)
•Rock forming minerals
25

26. 26
Chemical Classification of Minerals (Groups of Minerals)
➢Mineralareclassifiedonthebasesoftheirchemical
composition,andthemostcommononcearethe
following:
CHEMICAL
FORMULA
MINERALCHEMICAL GROUP
AuGold
Metallic
minerals
(I)
NATIVE
MINERALS
AgSilver
PPlatinum
CuCopper
SSulphur
Non-Metallic
Minerals CDiamond

27. 27
CHEMICAL
FORMULA
MINERALCHEMICAL GROUP
Fe2O3Hematite
OXIDES
(2)
OXIDES
AND
HYDROXIDES
Fe3O4Magnetite
FeTiO3Ilmenite
Al2O3Corundum
FeCr2O4Chromite
TiO2Rutile
UO2Uranenite
MnO2Pyrolusite
Fe2O3. 2H2OLimonite
HYDROXIDES
MnO2.nH2OPsilomelane
Mn2O3.H2OManganite
Fe2O3.nH2OGoethite

28. 28
CHEMICAL
FORMULA
MINERALCHEMICAL GROUP
pbSGalena
(5)
SULPHIDES
HgSCinnabar
FeS2Pyrite
CuFeS2Chalcopyrite
ZnSSphalerite
NaClHalite
(6)
HALIDES
KClSylvite
CaF2Fluorite
Na3AlF6Kryolite

29. 29
CHEMICAL
FORMULA
MINERALCHEMICAL GROUP
(Fe,Mn)WO4Wolframite
(7)
TUNGESTATES
CaWO4Schellite
(Ce,La,Nd,Th)(PO4,
SiO4)
Monazite
(8)
PHOSPHATES
Ca5(PO4)3Apatite
CuAl6(PO 4)
4(OH) 8·4H 2O
Turquoise
(9)
SILICATES

30. 30
(9) SILICATES
➢Averycommonmineralgroupconstitutesmorethan95%of
theearth’scrust.
➢SilicatemineralsareessentiallycomposedofSi-O4
tetrahedron
➢Tetrahedraarethebasicbuildingblocksofallsilicate
minerals.
➢AccordingtotheproportionandarrangementoftheSi-O4
tetrahedra,silicatemineralsareclassifiedinto6Categories.

31. 31
A.Single Solitary SiO4-Tetrahedron Minerals: Neso Silicates
(Independent or isolated )
➢ThesearesilicatemineralscomposedofonlyONESi-O4
tetrahedron ➢The basic unit is (SiO4)
4-
➢The Si:O ratio is 1:4
➢They have (-4 free electrons)
example Zircon ZrSiO4
B.Soro Silicates (Twin Tetrahedral Structure)
➢ThesearesilicatemineralscomposedofonlytwoSi-O4
tetrahedral.Thetwosilicatesaresharingoneoxygen.
➢Basic unit (Si2O7)
6-
➢Has (-6 free electrons)
➢The Si:O ratio is 2:7,example melilite
Ca2MgSi2O7

32. ➢Ringoftetrahedralformastwooxygenofeachtetrahedron
basedontheadjacenttetrahedralinaclosedrings.
➢Ringmaylinkthree,fourorsixtetrahedral
C.Single Ring SiO4-Tetrahedra Minerals: (Cyclo-Silicates)
The basic unit is (SiO3)n , n=3,4,6
1)Triad-Ring Silicate minerals such as:(3-fold)
oThe basic unit is (SiO3)3, i.e. n=3
oThe Si:0 is 1:3
oHas (-6 free electrons).
Example
Wollastonite…………..CaSiO3
Bentonite ……………. BaTi(SiO
3)
3

33. 33
2)Tetrad-Ring Silicate minerals (4 Fold)
oThe basic unit is (SiO3)4, i.e. n=4
oThe Si:0 is 1:3
oHas (-8 free electrons).
3)Hexa-Ring Silicate minerals (6 Fold)
oThe basic unit is (SiO3)6, i.e. n=6
oThe Si:0 is 1:3
oHas (-12 free electrons).
Example
Beryl…………… .Be
3Al
2(SiO
3)
6

34. 34
D.Chain SiO4-Tetrahedra Minerals (Ino silicates)
➢There are two sub types of these chain silicates (Inosilicates):
1)Single chain silicate
2)Double chain silicate
1) Single Inosilicates (Single Chain Silicates)
➢Iftwooftheoxygen'saresharedinawaytomakelongsinglechains
oflinkedSiO
4tetrahedral,wegetthesinglechainsilicatesor
Inosilicates.
➢InthiscasethebasicstructuralunitisSi
2O
6
-4
orSiO
3
-2
.Thisgroupis
thebasisforthepyroxenegroupofminerals,liketheorthopyroxenes
(Mg,Fe)SiO
3ortheclinopyroxenesCa(Mg,Fe)Si
2O
6.

35. 35
2) Double Inosilicates(Double Chain Silicates)
➢Iftwochainsarelinkedtogethersothateachtetrahedralgroup
shares3ofitsoxygen's,wecanfromdoublechains,withthebasic
structuralgroupbeingSi
4O
11
-6
.
➢Theamphibolegroupofmineralsaredoublechainsilicates,for
examplethetremolite-ferroactinoliteseriesCa
2(Mg,Fe)
5Si
8O
22(OH)
2.
Amphibole-Mg
7Si
8O
22(OH)
2.

36. 36
E.Sheet SiO4-Tetrahedra (Phylo silicate) Minerals
➢If3oftheoxygen'sfromeachtetrahedralgrouparesharedsuchthat
aninfinitesheetofSiO
4tetrahedralaresharedwegetthebasisforthe
Phyllosilicatesorsheetsilicates.
➢InthiscasethebasicstructuralgroupisSi
2O
5
-2
.Themicas,clay
minerals,chlorite,talc,andserpentinemineralsareallbasedonthis
structure.

37. 37
F.Tecto-Silicates (frame Work silicate)
➢Alltheoxygenshared
➢Si:O=1:2
E.g.Quartz,Feldspars

38. 38
2.1.3 Rock-formingMinerals
➢Althoughabout3500mineralsareknowntoexistinthe
Earth’scrust,onlyasmallnumber,between50-100,are
importantbecausetheyarecommonorvaluable.
➢Therock-formingmineralsmakeupthebulkofmostrocksin
theEarth’scrust.
➢Theyareimportanttogeologistssimplybecausetheyarethe
mostcommonminerals.
➢Theyareolivine,pyroxene,amphibole,mica,theclay
minerals,feldspar,quartz,calcite,anddolomite.

39. 39
➢Olivineisanindependenttetrahedralsilicatemineralthat
occursinsmallquantitiesinbasaltofbothcontinentaland
oceaniccrust.
▪However,rockscomposedmostlyofolivineand
pyroxenearesupposedtomakeupmostofthemantle.
➢Thepyroxenesareagroupofsinglechainsilicates
▪Pyroxenesareamajorcomponentofbothoceanic
crustandthemantleandarealsoabundantinsome
continentalrocks.
A) Silicates Rock forming Minerals

40. 40
➢Theamphibolesareagroupofdouble-chainsilicates
withsimilarproperties.Theyoccurcommonlyinmany
continentalrocks.
➢Themicasaresheetsilicatesandtypicallygrowasplate-
shapedcrystals,withflatsurfacesMicaiscommonin
continentalrocks.Theclaymineralsaresimilartomica
instructure,composition,andplatyhabit.
➢Feldsparandquartzaregroupofframeworksilicates.
Thefeldsparsmakeupmorethan50percentoftheEarth’s
crust.Quartzisabundantincontinentalrocksbutrarein
oceaniccrustandthemantle.
A) Silicates Rock forming Minerals

41. 41
➢The silicate minerals contain the (SiO4)4-complexanion.
➢Silicates make up about 95 percent of the Earth’s crust. They
aresoabundant for tworeasons.
oSiliconand oxygen are the two most plentiful elements in
thecrust.
oSilicon and oxygen combinereadily.
Silica
(SiO
4)
4-
Why silicates are dominant?

42. 42
B) Non-silicates Rock Forming Minerals
➢Thecomplexcarbonateanion(CO3)2-isthebasisoftwo
commonrock-formingminerals,calcite(CaCO3)and
dolomite[CaMg(CO3)2].
➢Mostlimestoneiscomposedofcalcite,anddolomitemakes
upthesimilarrockthatisalsocalleddolomiteor
sometimesdolostone.
Carbonates
Fig. Calcite (a) and dolomite (b) are two rock-forming carbonateminerals.

43. Summary
•Mineralareclassifiedonthebasesoftheirchemical
composition,andthemostcommononcearenativeminerals,
Oxides,Hydroxides,Halides,PhosphateandSilicatesetc.
•SilicatesmineralsrichrockaremostabundantoftheEarth’s
crust.
•Olivine,pyroxene,amphibole,mica,feldsparandquartz
aresilicaterockformingminerals
•Calcite,anddolomitearenon-silicaterockformingminerals
43

44. Thank you
44

45. Today Agenda
•Rock and types of rocks
•Engineering consideration of rocks
46

46. 47
2 .2 Rocks
➢Rockissolidmixtureoftwoormoreminerals.
➢Thefigurebelowshowstherockcycle.
Three types of rocks.
▪Igneous
▪Sedimentary
▪Metamorphic
2.2.1DefinitionofRocksAndRockCycle

47. 48
2.2.2.1 Igneous Rocks
➢Igneousrockisdefinedasanyrockthathascooledfrom
moltenrock.
2.2.2 Types of Rocks

48. 49
IntrusiveIgneousRocks-Rocksthatcoolfromamelt
belowtheground.
oExample:Granite,Gabbro,pegmatite,Diorite,
Granodioriteetc.
ExtrusiveIgneousRocks–Rocksthatcoolfromamelt
abovetheground.
oExampleBasalt,Scoria,Rhyolite,Ignimbrite,Pumice,
Tuff,,Obsidian,etc.
Classification of Igneous Rocks
A) Based on Mode of Formation

49. 50
B) Based on Ferro-Magnesian Content
➢Igneousrocksareclassifiedintotwocategoriesbasedon
theirferromagnesiancontent.
(a)Dark(orferromagnesian)silicates
➢Olivine,pyroxene,amphibole,andbiotitemica.
Example,Basalt,Gabbro,Scoria,etc.
Basalt Gabbro

50. 51
b)Light(ornon-ferromagnesian)silicates
➢Quartz,muscovitemica,andfeldspars
Example,Rhyolite,IgnimbriteGranite,Pumice,Tuff,
Granodioriteetc.
Rhyolite PumiceGranite

51. 52
(i)Granitic(AcidicRocks)
▪Termed felsic(feldspar and silica) in composition
▪High amounts of silica (SiO
2)
▪Light-colored silicates
▪Major constituent of continental crust
(ii)Basaltic(BasicRocks)
▪Termed mafic(magnesium and iron) in composition
▪Dark silicates and calcium-richfeldspar
▪Higher density than granitic rocks
▪Comprise the ocean floor and many volcanic islands
C) Based on Silica Content

52. 53
Other compositional groups
(iii) Intermediate (or andesitic) composition
▪Contain 25% or more dark silicate minerals
▪Associated with explosive volcanic activity
(iv) Ultramafic composition
▪Rare composition that is high in magnesium and iron
▪Composed entirely of ferromagnesian silicates

53. 54
1)The use of igneous rocks as aggregate in Portland cement
concrete can cause problems.
▪AcidicIgneousrocks(igneousrockswithgranitic
composition,Pyroclasticrocks,Eg.Tuff,Volcanic
breccia,Obsidian,andPumice)havehighsilicacontent
andthus,theycancausealkali-silicareactionproblems
2)Verycoarsegrainedigneousrocksareundesirableforuse
asaggregatesforconstruction.
oWithincreasinggrainsize,abrasionresistanceis
reduced,andtherockislesssuitableforuseasabase
course(roadbase),concreteaggregate,orsourceof
riprap(largestoneusedforslopeprotectionalongrivers
andseacoasts).
Engineering considerations of igneous rocks

54. 55
3)Thepresenceofcertainmineralsinigneousrocksmakesthe
rockundesirableforsomeengineeringuses.
oZeolite minerals are undesirable in aggregates that will
be exposed to the weathering process.
4)Infoundationsforengineeringstructuressuchasdams,
bridgepiers,andundergroundinstallations,weathered
igneousrockand/oranyotherrockistobeavoided.
oExcavation must extend through this material into sound
rock.
Engineering considerations of igneous rocks

55. 56
2.2.2.2 Sedimentary Rocks

56. 57
➢Sedimentaryrocksareformedbycompactionofclasts,a
chemicalprecipitate,orandevaporativeresidue.
oClast–Aparticleofarock.
oChemicalprecipitate–afinepowderthatcomesoutof
solution.
oEvaporativeresidue–afinepowderleftoverwhenwater
withmineralsdissolvedinitevaporates.
A) Introduction

57. 58
B) Types of sedimentary rocks
➢Sedimentoriginatesfrommechanicaland/orchemical
weathering.
➢Hencebasedontheirmodeofformation,sedimentaryrocks
areclassifiedintotwocategories.
1)(Clastic)Detritalrocks
oTheyaresedimentaryrocksthatareformedfrom
compactionandcementationofpre-existingrocks
2)(Non-Clastic)Chemicalrocks
Theyaresedimentaryrocksformedfromcompacted
precipitatesorevaporateresidues.

58. 59
1) Detrital (Clastic) sedimentary rocks
➢Clasticsedimentaryrocksarethosewhichwereformed
frombrokenrockpieces.
➢Thus,thesetypesofsedimentaryrocksaredifferentiated
fromoneanotherbyparticlesize.

59. 60
Types of detrital sedimentary rocks
Common detrital sedimentary rocks:
(i) Shale
oMud-sized particles in thin layers that are commonly
referred to as laminea
oMost common sedimentary rock
oNaturally it poses very low bearing capacity
(ii) Sandstone
oComposed of sand-sized particles
oForms in a variety of environments
oQuartz is the predominant mineral

60. 61
oAlternatingsequencesofshaleandsandstoneexposedintheGrand
Canyon.
oShalecannotsupportsteepcliffsorformerosionalescarpments

61. 62
(iii) Conglomerate and Breccia
✓Botharecomposedofparticlesgreaterthan2mmin
diameter
✓Conglomerateconsistslargelyofroundedgravels;often
hasasimilarappearanceto“concrete”
✓Brecciaiscomposedmainlyoflargeangularparticlesand
fragments,whichhavenotbeenrounded
Conglomerate Breccia

62. 63
TypesofChemicalsedimentaryrocks
(a) Limestone
oMostabundantchemical
rock
oComposedchieflyofthe
mineralcalcite
oItverysolublerock
➢Consistofprecipitatedmaterial
thatwasonceinsolution.
➢Precipitationofmaterialoccurs
by:(a)inorganicprocesses,(b)
organicprocesses(biochemical
origin)
2) Chemical sedimentary rocks
Diagramshowingthecarboncycle,with
emphasisonflowofcarbonbetweenthe
atmosphereandhydrosphere

63. 64
(b) Evaporites
➢Examplesincluderocksalt;
gypsum(usedfordrywall,
aspirin,andpotash(usedfor
fertilizer)
(c) Coal
▪Differentfromotherrocks
becauseitiscomposedof
organicmaterial
▪Stagesincoalformation(in
order):Plantmaterial,Peat,
Lignite,Bituminousand
Anthracite.

64. 65
1)Certainsedimentaryrockscanbeinvolvedinthealkali-
silicareactionprobleminPortlandcementconcrete.
Eg.Chert.
2)Limestoneanddolomiteprovidethebestsedimentary
aggregatesforconstructionmaterials.
oSiltstone,shale,quartzsandstone,andconglomerateare
generallynotacceptable.
3)Coarse-grainedlimestonesabradetooseverelytobeused
foraggregatesforconstruction.
oSuchrockparticipleslosegradationowingtoareduction
inparticlesize.
Engineering considerations of sedimentary Rocks

65. 66
4)Sedimentaryrocksusedasdimensionstoneforthefacingof
buildingsshouldbenon-stainingandresistanttoweathering
effects.
5)Limestones,dolomites,andevaporitedepositscanexhibitan
irregularsoil-rockinterfaceintheirweatheringprofiles.
oCaremustbetakentoensurethatheavystructuresarefounded
completelyonsolidrock.
6)Sinkholesandundergroundconduitsinlimestonesanddolomites
mustberecognizedandproperlydealtwithwhenfounding
buildingsintheseterrains.
7)Whenwaterisimpoundedbehindadam,iflimestoneliesatthe
rimorwithinthereserviorarea,carefulconsiderationisrequired.
oThepresenceofsolutionchannelsinsuchrockscanleadto
leakageunlessthechannelsarefilledbygroutingorother
techniques.

66. 67
8)Conglomeratesarebasicallyweaksedimentaryrocks
becausetheyarepoorlycementedandhighlyporous.
oWatermovementthroughthisrockremovesthecement
andincreasespermeability.
oWhenencounteredindamabutmentandfoundations,
conglomeratesrequirespecialtreatmenttoincrease
theirstrengthandreducepermeability.
9)Sedimentaryrockscontaininganhydritearetroublesometo
engineeringstructuressuchasdams,highways,andtunnels
becausethemineralwillaltertogypsuminthepresenceof
water,yieldinganincreaseinvolumeandconsiderable
stressonthestructureadjacenttoit.
oThepresenceofanhydritemustberecognizedandsteps
takentoreduceitseffect.

67. 68
2.2.2.3 Metamorphic Rocks

68. 69
What are Metamorphic Rocks?
➢Metamorphicrock:rocksthathavebeenchangedbyheat
andpressurewithoutmelting.
➢Metamorphismisthetransitionofonerockintoanotherby
temperaturesand/orpressuresunlikethoseinwhichit
formed.
➢Metamorphicrocksareproducedfrom:
1)Igneousrocks
2)Sedimentaryrocks
3)Othermetamorphicrocks
Orthmetamorphicrocksthathavebeenoriginatedfrom
igneous,Example:Gneiss
Parametamorphicrocksthathavebeenoriginatedfrom
sedimentaryrocks,Examples:Marble

69. 70
What are Agents of Metamorphism?
➢Most important agent.
➢Recrystallization results in new, stable minerals.
➢Two sources of heat:
1)Contactmetamorphism–heatfrommagma.
2)Anincreaseintemperaturewithdepthduetothe
geothermalgradient.
(a) Heat

70. 71
(b) Pressure and differential stress
➢Increaseswithdepth.
➢Confiningpressureappliesforcesequallyinalldirections.
➢Rocksmayalsobesubjectedtodifferentialstresswhichis
unequalindifferentdirections.
Regional metamorphism caused by differential stress associated with
mountain building

71. 72
(c) Chemically active fluids
❑Mainly water with other volatile components.
▪Enhances migration of ions.
▪Aids in recrystallization of existing minerals.
Sources of fluids:
-Pore spaces of sedimentary rocks.
-Fractures in igneous rocks.
-Hydrated minerals such as clays and micas.

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What are types of Metamorphism?
1)Contact or thermal metamorphism
▪Itisthetypeofmetamorphismthatisdrivenbyarisein
temperaturewithinthehostrock.
▪Ithappenswhenrockisheatedupbyanintrusionofhot
magma

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2)Hydrothermal metamorphism
➢Itisatypeofmetamorphismwhichoccurswhencountry
rocksarechemicalalteredbyhot,ion-richwater.
Hydrothermal metamorphism

74. 75
3)Regional metamorphism
➢Occurs during mountain building
➢Produces the greatest volume of metamorphic rock
Regionalmetamorphismoccurswhenrocksaresqueezedbetweenconvergingplates
duringmountainbuilding.

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➢Progressiveregionalmetamorphism:fromlowgrade(slate);to
highgrade(gneiss)

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Common metamorphic rocks
(i) Foliated rocks
(a)Slate
➢Veryfine-grained
➢Excellentrockcleavage
➢Mostoftengeneratedfromlow-grademetamorphismofshale,
mudstone,orsiltstone
(b) Phyllite
➢Gradation in the degree of metamorphism between slate and
schist.
➢Platy minerals not large enough to be identified with the
unaided eye.
➢Glossy sheen and wavy surfaces.
➢Exhibits rock cleavage.
➢Composed mainly of fine crystals of muscovite and/or chlorite.

77. 78
Slate(left)andphyllite(right),whichismorewavyandshiny)

78. 79

79. 80
(c) Schist
oMedium-tocoarse-grained
oPlatyminerals(mainlymicas)predominate
oThetermschistdescribesthetexture
oToindicatecomposition,mineralnamesareused(suchas
micaschist)
Garnetmicaschistisahighgrade
metamorphicrockwhereindividual
platesofshinymicaareeasilyvisible.
Thedarkredgarnetcrystalsarecalled
almandine.

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(d) Gneiss
–Medium-to coarse-grained
oBandedappearance
oHigh-grademetamorphism
oOftencomposedofwhiteorlight-coloredfeldspar-rich
layerswithbandsofdarkferromagnesianminerals

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(a) Marble
oParent rock was limestone or dolostone
oUsed as a decorative and monument stone
oExhibits a variety of colors
Marble is a crystalline rock formed by the metamorphosis of limestone
(ii) Non-foliated rocks

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(b) Quartzite
oFormed from a parent rock of quartz-rich sandstone
oQuartz grains are fused together
Quartziteisanon-foliatedmetamorphicrockformedfromquartz
sandstone.Itisveryhardandresistant,andcanbetaxingon
constructionequipment.

83. 84

84. 85
1)Foliatedmetamorphicrockscommonlyyieldsrockpieces
withelongatedshapeswhencrushed.
oTheserockscouldcausemixingproblemsinfresh
concreteanddirectionalpropertiesinhardenedconcrete.
2)Foliatedrockspossesprominentdirectionalproperties.
oStrengthandpermeabilityareaffectedbythedirectionof
foliation.
oCareshouldbetakenthatloads(frombridges,dams,
buildings,andfoundations)arenottransferredto
foliatedrockmassesinadirectioncloselyparalleltothe
foliation.
Engineering Considerations of Metamorphic Rocks

85. 86
3)Metamorphic rocks may be deeply weathered and the
depth to bedrock is quite variable.
oCaremustbetakentofoundheavystructures,ortolocated
tunnelalignments,insoundrockwheneverpossible.
4)Slate,schist,andphyllitearesubjecttorockover-break
duringblastingofrockcutsortunnelsbecauseoftheir
pronouncedrockcleavage.
oHighstressconcentrationsintunnelsmayoccurforthe
samereason.
Engineering Considerations of Metamorphic Rocks

86. 87
5)Thestabilityofrockslopesisgreatlyaffectedbythe
orientation(attitude)offoliationwithrespecttotherock
slopedirection.
oWhenfoliationdipssteeplyintoanopening,rockslides
commonlyoccur.Rockboltsmaybeneededtoprevent
suchfailures.
6)Marble is subject to the same problems as limestone.
oSolutioncavitiesandchannelsmaydevelop,resultingin
similarproblemsofleakageofreservoirandcollapseof
newlyformedsinkholes.
Engineering Considerations of Metamorphic Rocks

87. Summary
•Rockis solid mixture of two or more minerals.
•There are three common types of rocks
•Igneous
•Sedimentary
•Metamorphic rocks
88

88. Next class
Chapter 3
Geological Work of Natural Agencies
89

89. Thank you
90