Study of rocks and types of rocks - Petrology.pdf

Study of rocks Petrology

1. PETROLOGY
Unit -1
Chapter 2
Dr. A. Suchith Reddy
Associate Professor

2. ➢INTRODUCTION TO PETROLOGY
➢GEOLOGICAL CLASSIFICATION OF ROCKS
➢ROCK CYCLE
➢DYKES AND SILLS
➢COMMON TEXTURE
➢STRUCTURES
➢PHYSICAL AND ENGINEERING PROPERTIES OF ROCKS
➢CIVIL ENGG. IMPORTANCE

3. PETROLOGY AND ITS DEFINITION
Petrology(fromGreek:Petra,rock; andlogos,
knowledge)isthebranchofGEOLOGY thatstudies
rocks,andtheconditionsinwhichrocksform.
Thesubjectmatterof PETROLOGYconsiststheorigin,
association,occurrence,mineralcomposition,chemical
composition,texture,structure,physicalproperties,etc.,
ofrocks.
WhereasPETROGRAPHY dealswiththedescriptive
partofrocksandPETROGENYdeals withthemodeof
formationofrocks.
Thesetwotogethermakeup Petrology.

4. DEFINITION OF ROCK
Natural solid massive aggregate of minerals forming the
crust of the earth.
(or)
An unit of the earth’s crust which is formed with minerals.

5. GEOLOGICAL CLASSIFICATION OF ROCKS
❖Therocksareclassifiedinvariouswaysbasedondifferentprinciplessuchas
Physical,Chemical ‘n’Geological Classifications.
❖Among the different classifications, Geologicalclassificationofrocksisthemost
properbecausegroupingofrocksismorelogical,lessambiguous,orderlyand
comprehensive.
❖The Geologicalclassification ofrocksisbasedontheirMODEOFORIGIN.
Theyare………..
1)IGNEOUSROCKS
2)SEDIMENTARYROCKSand
3)METAMORPHIC ROCKS.

6. The rock cycle is the natural process by
which rocks change from one type to
another over geological time. It helps
explain how the Earth's crust is recycled
and why different types of rocks have
different properties useful in construction
and engineering.
Ortho-metamorphic: (igneous to
sedimentary).
Para-metamorphic: (sedimentary to
igneous).
Poly-metamorphism:
(when rock undergo metamorphism
more than once).
ROCK CYCLE

7. Formation of Igneous Rocks
•How: When magma (molten rock
beneath the Earth's surface) cools and
solidifies, it forms igneous rocks.
•If it cools inside the Earth →
Intrusive igneous rocks (e.g.,
Granite)
•If it cools on the surface after a
volcanic eruption → Extrusive
igneous rocks (e.g., Basalt)
•Civil Engineering Relevance:
Igneous rocks are strong and
durable, used in foundations, roads,
and buildings.
Weathering and Erosion
•How: Over time, igneous (or other) rocks break down into
small particles (sediments) due to:
•Weather (rain, temperature)
•Wind, rivers, glaciers
•These sediments are transported by water, wind, or ice.

8. Formation of Sedimentary Rocks
•How: Sediments get deposited in layers,
usually in rivers, lakes, or oceans.
•Over time, they undergo compaction
and cementation to form sedimentary
rocks like sandstone, limestone, and
shale.
•Civil Engineering Relevance: Some
sedimentary rocks (like limestone) are used
for cement, but others (like shale) are weak
and unsuitable for heavy structures.

9. Formation of Metamorphic Rocks
•How: When igneous or sedimentary
rocks are subjected to intense heat and
pressure, they change their form and
structure, becoming metamorphic
rocks.
•Example: Limestone → Marble,
Shale → Slate
•Civil Engineering Relevance:
Metamorphic rocks like marble and
slate are used in flooring, facades, and
sometimes in structural elements (if
strong enough).
Melting:
How: If metamorphic rocks are subjected to even
more heat, they can melt and turn into magma
again.
The cycle restarts as this magma can cool and form
igneous rocks.

10. Reason Explanation
Site selection
Understanding rock type helps in
selecting suitable land for construction.
Material choice
Helps engineers choose the right rock
(e.g., granite for strength, marble for
appearance).
Foundation design
Properties like compressive strength
and porosity vary by rock type.
Tunneling and Dams
Rock behavior under pressure and
water flow is crucial for safety.
Why Civil Engineers Study the Rock Cycle

11. Property Description Importance in Engineering
Color
Visual appearance due to mineral
composition.
Useful for preliminary identification, though not a
reliable engineering property.
Grain Size Size of individual mineral particles.
Affects strength and porosity. Finer grains often
mean denser and stronger rocks.
Texture
Arrangement and size of grains or
crystals.
Influences workability and strength.
Specific
Gravity
Ratio of rock density to water
density.
Indicates density; used in weight and stability
calculations.
Porosity Percentage of void space in a rock.High porosity may reduce strength and durability.
Permeability
Ability of water to flow through
rock.
Important in dam, tunnel, and foundation design.
Hardness
Resistance to scratching (Mohs
scale).
Indicates abrasion resistance. Harder rocks are
preferred for road construction.
Durability
Resistance to weathering and
decomposition.
Affects long-term performance of structures.
Physical Properties of Rocks

12. Property Description Importance in Civil Engineering
Compressive
Strength
Maximum compressive stress a
rock can withstand.
Crucial for load-bearing structures (e.g.,
foundations, columns).
Tensile Strength Resistance to being pulled apart.
Low in rocks; important in slope stability and
blasting.
Shear Strength Resistance to shearing forces.
Key in slope stability, landslide analysis, and
tunnel design.
Modulus of
Elasticity (E)
Ratio of stress to strain in elastic
range.
Used in stress-strain analysis and deformation
prediction.
Poisson’s Ratio Ratio of lateral to axial strain.
Helps in understanding deformation
characteristics.
Rock Quality
Designation (RQD)
Measure of rock mass quality
from core samples.
Used in tunnel, foundation, and excavation
assessments.
Weatherability
Resistance to degradation due to
climate.
Affects lifespan of rock structures exposed to
environment.
Slake Durability
Index
Measures resistance to
weakening in wet-dry cycles.
Important for rocks exposed to fluctuating
moisture (e.g., in embankments).
Engineering Properties of Rocks

15. IGNEOUSROCKS
Theseareprimaryrocks,Most
abundantrocksintheearth’scrust.
Theseareformedataveryhigh
temperatureandpressureconditions
directlyasaresultofsolidificationof
magmaorlava.
MAGMA:Thetermmagmais
appliedwhenthemeltis
underground.
LAVA:Themeltwhenitreachesthe
earth’ssurfaceandflowsoverit, is
calledlava.
SOMEIGNEOUSROCKS

16. Types of Igneous rocks
❖VolcanicorExtrusive
❖PlutonicorIntrusive
❖Hypabyssal

17. Volcanic/Extrusive rocks
▪Rocks that results when lava solidifies
▪These rocks cools quickly and usually has small grains
▪Some rocks cools so fast and don’t has grains at all
Eg: The Deccan traps of India spread over more than 4 lakh
sq.km in Peninsular India

18. Whenlavacools,
extrusiveigneous
rockisformed.

19. Melt
✓liquidportionofamagmabody.
✓composedofionsthatmoveabout freely.
Crystallization
✓randommovementsoftheionsslow, andtheionsbegin
toarrange themselvesintoorderlypatterns.

20. ➢coolingstronglyinfluencescrystalsize.
✓slowcoolingresultsintheformationof largecrystals.
✓quickcoolingresultstheformationof solidmassof
smallintergrowncrystals.

21. Rocks with small grains
Basalt
Granite
Andesite
Olivine
Pumic

22. Plutonic/Intrusiverocks
•Rocks that results when magma solidifies
•Rocks that formed at considerable depths between 7-10 sq.km below the
surface of the earth
•These rocks cools quickly and usually has large grains

23. Whenmagmacools,itforms
intrusiveigneousrock

24. Granite
Syenite
Pegmatite
Diorite
Plutonic rocks

25. Hypabyssalrocks
▪These are formed at intermediate stage below the earth surface
▪Rocks that formed at considerable depths up to 2kms
▪They show mixed character of volcanic and plutonic rocks
▪Eg: porphyries with different compositions

26. DykesandSills
❖Mostcommonformsofigneou
rocks
❖Dykesarediscordant,sheetlike
structures,vertically or
inclined.
❖Dykesareformedbytheintrusionof
magma intopre-existingfractures.
❖Thoseigneousintrusionsthathave
been injectedalongorbetweenthe
beddingplanes areSills.

27. TypesofDykesandSills
Dykes
▪Simpledykes
▪Multipledykes
▪Composite dykes
▪Ringdykes
Sills
▪Simplesills
▪Multiplesills
▪Compositesills
▪Differentiatedsills
▪Interformationalsills

28. Commonstructuresofigneous rocks
Physicalappearanceofrocksincludingsize, shapeandforms.
Types
➢Vesicularstructure
➢Amygdaloidalstructure
➢Columnarstructure
➢Sheetstructure
➢Flowstructure&
➢Pillowstructure

29. Vesicular structure:
Vesicularstructureis a
volcanicrock
structurecharacterized byarock
beingpitted withmanycavities
(knownasvesicles)at
itssurfaceandinside.
Basalt

30. Amygdaloidalstructure:
❖Thedropinpressurethataexperiencesasitflows
fromundergroundtotheEarth'ssurfaceallows
waterandgasesinthelavatoformbubbles.
❖Ifthebubblesdonotgetlargeenoughtopop,
theyarefrozeninthelavaasvesicules.
❖Amygdaloidsaresimplyvesiclesthathavebeen
filledinwithasecondaryminerallongafterthe
flowcooled.
❖Suchsecondarymineralsarecommonlywhite:
quartz,calcite,orzeolite.(Asecondarymineralis
onethatformedaftertherockoriginallyformed.)
Olivinebasalt

31. Columnar Structure
Mineralaggregate thatis
madeupof nearlyparallel
slendercolumns andthatis
intermediate
betweenanequant and
acicular
structure(asin some
amphiboles)
Columnar Basalt

32. Sheetstructure
Thedevelopmentof onesetof
welldefined jointssometimes
bringsaboutaslicing effect
onthemassive igneousrock
body.
If allsuchslicesare horizontal,
the structureissaidtobe sheet
structure.
Rock with mica sheets

33. Flow structure:
▪Thesestructureisplanarorlinearfeaturesthat resultfromflowage
ofmagmawithorwithout containedcrystals.
▪Variousformsoffaintlyto sharplydefinedlayeringandlining
typically reflectcompositionalortexturalin homogeneities,and
theyoftenareaccentuatedby concentrationsorpreferred
orientationof crystals,inclusions,vesiclesandotherfeatures.

34. Pillow
▪These structures consists of aggregates ofvoid
masses,resemblingpillows orgrain-filledsacksin
sizeand shape,thatoccurinmanybasic volcanic
rocks.
▪Themassesare separatedorinterconnected,and
eachhasathickvesicularcrustora thinnerand
moredenseglassyrind.
▪Theinteriorsordinarilyarecoarser-grainedand
lessvesicular.Pillow structureisformedbyrapid
chilling ofhighlyfluidlavain...

35. Sedimentsareloose,unconsolidated accumulationsofmineral
rockparticlesthat havebeentransportedbywind,water,ice,
gravityandre-deposited.
DerivedfromtheLatinsedimentummeans settling,referenceto
asolidmaterialsettling out ofa fluid.
Sedimentary Rocks

36. Sedimentary Rocks
❖Sedimentary rocks are formed when rocks settle out of water or air
❖Secondary rocks
❖There are 2 Types of
Sedimentary Rocks
❖Chemical
❖clastic
❖The rock pieces are then cemented together for form
Sedimentary Rocks
❖They also contain many fossils from millions of years ago!

37. Sedimentsarethe productsof
weathering.
Since theseare secondary materials
(i.e.,derivedfrompre-existing rocks),
therocks formedout of them arecalled
sedimentary or secondaryrocks.
Theoriginofsedimentaryrockstotally
relatedtotheweatheringinfluenceon
rocks.
Eg:Shale,Sandstone, Conglomerate,Flint,
Limestone

38. Sedimentaryrocksoftenlooklike
gluedtogetherrocks,pebbles,or
sand.
sandstoneconglomerate

39. Formation:
➢weatheringofpre-existingrockseitherby physicalbreakupintofiner
andfiner fragments,orbysolution.
➢precipitationofcrystalsoutofsolution.
➢usually,theparticlearebrokendown furtherduringthis
transportphase.
➢sedimentbecomelithified,orturnedto rock.
➢Somerocksformswhenwaterevaporates andmineralsleftbehind

40. Halite(salt)andgypsumare
formedthisway.

41. fossilsareoftenfoundinsedimentaryPlants&animalsare
caughtinthelayersofsedimentandleaveanimprintintherock.
rocksalt
FlintLimestone

42. Typesofsedimentaryrocks
Clastic(mechanically formed) rocks:
Clastic sedimentary rocks are rocks which are composed
predominantly of broken pieces of weathered and eroded rocks.

43. Chemically(Non-clastic)
Formed by
Chemical sedimentaryrockformswhenmineral constituents insolutionbecome
supersaturatedand inorganicallyprecipitate.
Commonchemical sedimentaryrocksincludeooliticlimestoneand rockscomposedof
evaporitemineralssuch ashalite(rocksalt),sylvite,bariteandgypsum.

44. TEXTURESOFSEDIMENTARY ROCKS
-originofgrains
-sizeofgrain
-shapeofgrain
-packingof grains

45. Common Structures of
Sedimentary Rocks
▪Sedimentarystructuresarethosestructuresformed duringsedimentdeposition.
Stratification:
Alayeredarrangementinsedimentaryrock. Differentlayersalsocalled
bedsorstratamaybe similarordissimilar.
Lamination:
layeredstructuresimilartostratificationbut layersarequitethin.

46. Cross bedding: layers lying above one another are not parallel having
inclined relation.
Gradedbedding:sedimentsarearranged accordingtotheirgrainsize.
Mudcracks:havingmanyfinesizedgrainswith irregularcracks.
Ripplemarks:symmetricalwave-like undulationsinalayer.

47. Metamorphic rocks
▪Metamorphismliterallymeanschange.
▪Thechangeinpre-existingrocksunderthe
influenceoftemperature,pressureand
chemicallyactivesolutions.
▪Themetamorphicrocksformedfromigneous
rocksarecalledOrthometamorphicrocksand
thoseformedfromsedimentaryrocksare
calledParametamorphicrocks.

48. ❖MetamorphicRocksarefoundinareasthathave beenunderlotsof
pressureand/ortemperature.
❖ex:mountains
❖Thereare2typesofMetamorphicRocks:
➢Foliated
➢Non-foliated
❖Theycanformfromeitherigneousrocksor sedimentaryrocks
Eg:Sandstonechangestoquartzite Granitechangesto
gneiss

49. Heat&pressurecanchange
sandstoneintoquartzite.

50. Granitecanbecomegneiss,

51. …and
shalecan
become
schist!

52. Types of Metamorphic rocks
❖Foliated:
Asaresultofcompressionandstressonthe
rock,themineralswithintherockalign
themselvesperpendiculartothedirectionof
stress.
❖Thisalignmentcreatesthe
banding/foliationinthe rock.

53. Non-foliated:
❖Ingeneral,manynon-foliatedrockshave
notundergoneagreatamountofstress,and
therefore,donotshowfoliation.
❖Also,themineralsthat composenon-
foliatedrocksareequidimensional
crystals.
❖Asaresult,nofoliationwouldappear
becauseallthemineralgrains looksimilar

54. COMMON STRUCTURESOFMETAMORPHIC ROCKS
The most common structures found in metamorphic rocks are;
1)Gneissose structure: bands of flaky minerals
2)Schistose structure: parallel layers
3)Granulose structure: having granular minerals

55. TEXTURE
 The size, form and orientation of clasts or minerals
in a rock is called its texture. The texture is a small-scale
property of a rock, but determined many of its large-scale
properties, such as the density, porosity or permeability

56. i.Coarse-grainedTexture
-appearanceofamassofintergrowncrystals,whichare
roughlyequalinsizeandlargeenoughtobeidentifiedwiththe
unaidedeye.

57. ii.PorphyriticTexture
-haslargecrystalsembeddedwitha matrixofsmaller
crystals.

58. iii.GlassyTexture
-resultswhentheionsdonothavesufficienttime
touniteintoanorderlycrystallinestructure.

59. Obsidian
-similartoa largechunkof
manufactured glass.
volcanicrock
thatexhibitsa
glassytexture.
Pumice

60. Property / Rock Type Granite Basalt Limestone Shale Sandstone
Rock Type Igneous Igneous Sedimentary SedimentarySedimentary
Color
Light (grey,
pink)
Dark (black,
green)
Light (white, cream)
Dark grey to
black
Reddish,
yellow
Grain Size Coarse Fine Fine to medium Very fine Medium
Hardness
High (6–7
Mohs)
Very High (6–8)Medium (3–4) Low (2–3) Medium (4–5)
Specific Gravity 2.6–2.8 2.8–3.0 2.3–2.7 2.2–2.6 2.3–2.6
Porosity Low Very low
High (in fossiliferous
types)
High Moderate
Permeability Low Very low High Very low High
Compressive Strength
(MPa)
100–250 150–350 30–100 10–50 20–170
Tensile Strength (MPa)7–25 10–30 2–15 1–10 2–15
Durability Very high Very high Medium to low Low Medium
RQD High High Medium Low Variable
Workability Difficult Very difficultEasy Very easy Easy
Comparison of common types of Rocks

61. CIVIL ENGINEERING IMPORTANCE OFPETROLOGY
Petrology is very important from civil engineering point of view, as it
provides a proper concept and logical basis for interpreting physical
properties of rocks.
The study of texture, structure, mineral composition, chemical
composition etc., gives all necessary details regarding the strength,
durabiliy, colour, appeareance, workability, etc.,
These inherent characters of rocks are of chief concern for a civil engineer
to judiciously assess the suitability occurring at project site for required
purpose.

62. IGNEOUSROCKS
SEDIMENTARY
METAMORPHIC
1.Granite. 1.Sandstone. 1.Gneiss.
2.Dolerite. 2.Limestone. 2.Quartzite.
3.Pegmatite. 3.Conglomerite. 3.Marble.
4.Basalt. 4.Shale. 4.Slate.
SOME COMMON EXAMPLES in CIVIL ENGINEERING

63. Common
Igneous Rocks
for
Identification

64. Granite
•Color: Light (white, pink, grey) with black mineral
specks.
•Texture: Coarse-grained; interlocking crystals.
•Hardness: 6–7 (Mohs).
•Density: 2.63–2.75 g/cm³.
•Porosity: Very low (<1%).
•Strength: High compressive strength (130–250 MPa).
•Durability: Excellent resistance to weathering.
•Uses: Foundations, columns, flooring, monuments.

65. Basalt
•Color: Dark grey to black.
•Texture: Fine-grained, compact; sometimes vesicular.
•Hardness: 6 (Mohs).
•Density: 2.8–3.0 g/cm³.
•Porosity: Low (dense basalt); higher if vesicular.
•Strength: 100–300 MPa compressive strength.
•Durability: Very high; good abrasion resistance.
•Uses: Road metal, railway ballast, retaining walls.

66. Diorite
•Color: Grey, greenish-grey, black-and-white
speckled.
•Texture: Coarse-grained; intermediate between
granite and gabbro.
•Hardness: 6–7 (Mohs).
•Density: ~2.8 g/cm³.
•Porosity: Very low (<0.5%).
•Strength: ~200 MPa compressive strength.
•Durability: Strong and weather-resistant.
•Uses: Decorative stone, paving, building facades.

67. Gabbro
•Color: Dark green, black.
•Texture: Coarse-grained, interlocking crystals.
•Hardness: 6–7 (Mohs).
•Density: 2.9–3.1 g/cm³.
•Porosity: Very low (<1%).
•Strength: 180–300 MPa compressive strength.
•Durability: Excellent.
•Uses: Flooring, countertops, construction aggregate.

68. Rhyolite
•Color: Light grey, pink, or beige.
•Texture: Fine-grained; may have visible quartz and feldspar phenocrysts.
•Hardness: 6–7 (Mohs).
•Density: 2.4–2.6 g/cm³.
•Porosity: Low.
•Strength: 100–150 MPa compressive strength.
•Durability: Good, but less tough than basalt.
•Uses: Decorative stones, aggregates.

69. Andesite
•Color: Grey, greenish-grey, brown.
•Texture: Fine-grained with occasional phenocrysts.
•Hardness: 6 (Mohs).
•Density: ~2.6 g/cm³.
•Porosity: Low (<1%).
•Strength: ~150 MPa compressive strength.
•Durability: Good; resistant to wear.
•Uses: Building blocks, paving stones.

70. Pegmatite
•Color: Light, often pink or white with large crystals.
•Texture: Very coarse-grained (crystals >1 cm).
•Hardness: 6–7 (Mohs).
•Density: ~2.6 g/cm³.
•Porosity: Very low.
•Strength: Similar to granite (~150–200 MPa).
•Durability: High.
•Uses: Decorative stone, countertops.

71. Obsidian
•Color: Black, dark brown, green.
•Texture: Glassy, smooth.
•Hardness: ~5–5.5 (Mohs).
•Density: 2.3–2.6 g/cm³.
•Porosity: Extremely low.
•Strength: Brittle despite high density.
•Durability: High, but prone to fracture.
•Uses: Decorative items, ornaments.

72. Pumice
•Color: White, light grey, pale brown.
•Texture: Highly vesicular, frothy appearance.
•Hardness: 6 (Mohs).
•Density: 0.25–1.0 g/cm³ (very light).
•Porosity: Very high (>60%).
•Strength: Low; crushable.
•Durability: Poor under heavy loads.
•Uses: Lightweight concrete, insulation, polishing.

73. Scoria
•Color: Dark brown, red, black.
•Texture: Vesicular, rough surface.
•Hardness: 5–6 (Mohs).
•Density: ~1.0–2.5 g/cm³.
•Porosity: High (30–50%).
•Strength: Low to moderate.
•Durability: Good for lightweight fill, not for
structural loads.
•Uses: Landscaping, drainage, lightweight concrete.

78. Common Sedimentary Rocks for Identification

80. Sandstone
•Color: Yellow, red, brown, grey, white (depends on cementing material and impurities).
•Texture: Medium to coarse-grained, clastic.
•Hardness: 6–7 (Mohs), because quartz is the dominant mineral.
•Lustre: Dull to vitreous.
•Density: 2.2–2.8 g/cm³.
•Porosity: Medium to high (5–30% depending on compaction and cement).
•Fracture: Uneven, granular.
•Specific Gravity: 2.2–2.8.
•Chemical Composition: Mostly SiO₂ (quartz) with feldspar, plus cementing agents like silica, calcite, or
iron oxide.
•Strength: 20–170 MPa (compressive), depending on cementing material and grain packing.
•Durability: High when silica-cemented; less in soft, calcareous types.
•Uses: Building stone, paving blocks, floor and wall cladding, ornamental features.

82. Limestone
•Color: White, grey, buff, bluish; sometimes dark due to organic matter.
•Texture: Fine to coarse-grained, crystalline or fossiliferous.
•Hardness: 3–4 (Mohs).
•Lustre: Dull to earthy; sometimes sub-vitreous in crystalline forms.
•Density: 2.3–2.7 g/cm³.
•Porosity: Low to medium (0.5–20% depending on type).
•Fracture: Conchoidal to uneven.
•Specific Gravity: 2.3–2.7.
•Chemical Composition: Mainly calcium carbonate (CaCO₃), with magnesium carbonate in dolomitic
limestone.
•Strength: 30–250 MPa (compressive); strong but not acid-resistant.
•Durability: Moderate; susceptible to acid rain and industrial pollution.
•Uses: Cement manufacture, building blocks, decorative stone, lime production.

83. Shale
•Color: Grey, black, brown, red, green.
•Texture: Very fine-grained, fissile (splits into thin layers).
•Hardness: 2–3 (Mohs).
•Lustre: Earthy to dull.
•Density: 2.2–2.6 g/cm³.
•Porosity: Low (<10%), but can hold water in pores.
•Fracture: Uneven to splintery; cleaves along bedding planes.
•Specific Gravity: 2.4–2.6.
•Chemical Composition: Clay minerals (kaolinite, illite), quartz, mica, organic matter.
•Strength: 5–80 MPa (compressive), drops when wet.
•Durability: Low; easily weathers and slakes in moisture.
•Uses: Bricks, roofing tiles, cement raw material.

84. Conglomerate
•Color: Variable (depends on pebbles and matrix).
•Texture: Coarse-grained, clastic, rounded pebbles in a fine matrix.
•Hardness: 6–7 (depends on pebble composition).
•Lustre: Dull to vitreous (from quartz pebbles).
•Density: 2.3–2.9 g/cm³.
•Porosity: Medium (5–15%).
•Fracture: Uneven; breaks around clasts.
•Specific Gravity: 2.4–2.8.
•Chemical Composition: Pebbles (quartz, chert, granite, etc.) in cement (silica, calcite, iron
oxide).
•Strength: 20–100 MPa (compressive); variable.
•Durability: Good if silica-cemented; poorer if clay-cemented.
•Uses: Decorative aggregate, occasionally building stone.

85. Breccia
•Color: Variable; often multicolored.
•Texture: Coarse-grained, angular rock fragments in fine matrix.
•Hardness: 6–7 (depends on fragments).
•Lustre: Dull to vitreous.
•Density: 2.3–2.9 g/cm³.
•Porosity: Medium (5–15%).
•Fracture: Uneven; breaks through matrix and fragments.
•Specific Gravity: 2.4–2.8.
•Chemical Composition: Angular rock fragments (quartzite, basalt, granite, etc.) in silica/calcite/iron
oxide cement.
•Strength: 20–100 MPa (compressive); depends on cementing.
•Durability: Good if silica-cemented; variable otherwise.
•Uses: Decorative facing stone, monuments.

86. Chalk
•Color: White to light grey.
•Texture: Very fine-grained, soft, powdery.
•Hardness: 1–2 (Mohs).
•Lustre: Earthy.
•Density: 1.8–2.3 g/cm³.
•Porosity: High (>30%).
•Fracture: Uneven, crumbly.
•Specific Gravity: ~2.3.
•Chemical Composition: Calcite (CaCO₃) from microscopic marine shells.
•Strength: 1–20 MPa (compressive); very weak.
•Durability: Low; easily weathers and dissolves in acids.
•Uses: Cement manufacture, agricultural lime, chalk writing sticks.

87. Siltstone
•Color: Brown, grey, reddish, yellowish.
•Texture: Fine-grained (between sandstone and shale).
•Hardness: 6–7 (Mohs) if quartz-rich; softer if clayey.
•Lustre: Dull to earthy.
•Density: 2.4–2.7 g/cm³.
•Porosity: Low to medium (5–15%).
•Fracture: Uneven, blocky.
•Specific Gravity: 2.5–2.7.
•Chemical Composition: Mostly quartz and feldspar with clay minerals.
•Strength: 20–100 MPa (compressive).
•Durability: Moderate; better than shale, poorer than well-cemented sandstone.
•Uses: Building stone, paving slabs, fill material.

89. Dolostone (Dolomite Rock)
•Color: Light grey, buff, pink.
•Texture: Fine to coarse-grained.
•Hardness: 3.5–4 (Mohs).
•Lustre: Pearly to vitreous in crystalline form.
•Density: 2.8–2.9 g/cm³.
•Porosity: Low to medium (0.5–15%).
•Fracture: Conchoidal to uneven.
•Specific Gravity: 2.85.
•Chemical Composition: Calcium magnesium carbonate (CaMg(CO₃)₂).
•Strength: 100–250 MPa (compressive).
•Durability: High in dry climates; less in acidic environments.
•Uses: Building stone, decorative stone, road base, source of magnesium.

90. Chert
•Color: White, grey, brown, red, green, black.
•Texture: Very fine-grained, hard, conchoidal fracture.
•Hardness: 7 (Mohs).
•Lustre: Waxy to vitreous.
•Density: 2.5–2.6 g/cm³.
•Porosity: Very low (<1%).
•Fracture: Conchoidal (smooth curved surfaces).
•Specific Gravity: 2.5–2.6.
•Chemical Composition: Microcrystalline quartz (SiO₂).
•Strength: 150–300 MPa (compressive).
•Durability: Very high; extremely resistant to weathering.
•Uses: Tool making (prehistoric), decorative stone, aggregate.

91. Gypsum Rock
•Color: White, grey, pink.
•Texture: Fine to medium-grained; sometimes fibrous or massive.
•Hardness: 2 (Mohs) — very soft.
•Lustre: Pearly to silky in fibrous form; vitreous in crystals.
•Density: 2.3 g/cm³.
•Porosity: Medium to high.
•Fracture: Conchoidal to uneven.
•Specific Gravity: 2.3.
•Chemical Composition: Calcium sulfate dihydrate (CaSO₄·2H₂O).
•Strength: Very low (compressive < 20 MPa).
•Durability: Poor in wet conditions; dissolves in water.
•Uses: Plaster of Paris, wallboards, cement additive, fertilizer.

94. Dolomite
Gypsum
Limestone
Chalk
Identify the Rocks………………..!!!
Silt Stone
Sandstone

95. Common Metamorphic Rocks for Identification

96. Contact metamorphismoccurs around igneous
intrusions, where the surrounding rock is
"baked" by the heat. Contact metamorphism
typically occurs at shallow crustal levels,
affecting rocks in a localized area.
Regional metamorphismoccurs over large
areas, typically at convergent plate boundaries
during mountain-building events. This type of
metamorphism is characterized by high
pressure and temperature due to tectonic
collision, producing foliated rocks like schist
and gneiss.
Burial metamorphism occurs in deep
sedimentary basins, where rocks are buried
under thick layers of sediments.

99. Marble
•Color: White, grey, pink, green, black (depends on impurities).
•Texture: Medium to coarse-grained, crystalline.
•Hardness: 3–4 (Mohs).
•Lustre: Vitreous to pearly.
•Density: 2.6–2.8 g/cm³.
•Porosity: Low (0.5–2%).
•Fracture: Uneven to conchoidal.
•Specific Gravity: 2.65–2.75.
•Chemical Composition: Calcite (CaCO₃) or dolomite (CaMg(CO₃)₂).
•Strength: 70–140 MPa (compressive).
•Durability: High in dry conditions; less durable in acidic environments.
•Uses: Flooring, wall cladding, sculpture, monuments.

100. Quartzite
•Color: White, grey, pink, red.
•Texture: Very fine to medium-grained, interlocking quartz crystals.
•Hardness: 7 (Mohs).
•Lustre: Vitreous.
•Density: 2.6–2.7 g/cm³.
•Porosity: Very low (<1%).
•Fracture: Conchoidal to uneven.
•Specific Gravity: 2.65.
•Chemical Composition: Quartz (SiO₂).
•Strength: 150–300 MPa (compressive).
•Durability: Very high; highly resistant to weathering and abrasion.
•Uses: Railway ballast, building stone, decorative stone.

101. Slate
•Color: Grey, black, green, purple.
•Texture: Very fine-grained, foliated; slaty cleavage.
•Hardness: 2.5–4 (Mohs).
•Lustre: Dull to slightly silky.
•Density: 2.7–2.9 g/cm³.
•Porosity: Low.
•Fracture: Splits into thin sheets along cleavage.
•Specific Gravity: 2.7–2.9.
•Chemical Composition: Clay minerals, mica, quartz.
•Strength: 100–200 MPa (compressive).
•Durability: High in most environments; excellent roofing material.
•Uses: Roofing tiles, flooring, chalkboards, billiard tables.

102. Schist
•Color: Grey, green, brown, silver.
•Texture: Medium to coarse-grained, strongly foliated (schistosity).
•Hardness: 4–5.5 (Mohs).
•Lustre: Often shiny due to mica content.
•Density: 2.6–2.9 g/cm³.
•Porosity: Low to medium.
•Fracture: Splits into thin, irregular slabs.
•Specific Gravity: 2.7–2.9.
•Chemical Composition: Mica, quartz, feldspar, garnet, chlorite.
•Strength: 80–200 MPa (compressive; varies with mineral content).
•Durability: Moderate; weaker along foliation planes.
•Uses: Decorative stone, facing, sometimes aggregate.

103. Gneiss
•Color: Banded grey, pink, black, white.
•Texture: Medium to coarse-grained, foliated (gneissic banding).
•Hardness: 6–7 (Mohs).
•Lustre: Dull to vitreous.
•Density: 2.6–2.9 g/cm³.
•Porosity: Very low (<1%).
•Fracture: Uneven, blocky.
•Specific Gravity: 2.65–2.9.
•Chemical Composition: Quartz, feldspar, mica, hornblende.
•Strength: 200–300 MPa (compressive).
•Durability: Very high; excellent in structural applications.
•Uses: Building stone, decorative panels, paving.
potassium feldspar (orthoclase) and sodium feldspar (albite).

104. Amphibolite
•Color: Dark green to black.
•Texture: Medium to coarse-grained, granular to weakly
foliated.
•Hardness: 5–6 (Mohs).
•Lustre: Sub-vitreous to silky.
•Density: 2.9–3.1 g/cm³.
•Porosity: Very low.
•Fracture: Uneven.
•Specific Gravity: 2.9–3.1.
•Chemical Composition: Amphibole (hornblende),
plagioclase feldspar.
•Strength: 150–250 MPa (compressive).
•Durability: High; good resistance to weathering.
•Uses: Roadstone, aggregate, building stone.

105. Phyllite
•Color: Silvery-grey, greenish-grey.
•Texture: Fine-grained, foliated, silky sheen from mica.
•Hardness: 2–4 (Mohs).
•Lustre: Silky.
•Density: 2.7–2.9 g/cm³.
•Porosity: Low.
•Fracture: Splits along foliation.
•Specific Gravity: 2.7–2.9.
•Chemical Composition: Quartz, mica, chlorite.
•Strength: 80–150 MPa (compressive).
•Durability: Moderate; weaker along cleavage.
•Uses: Roofing, wall cladding, decorative stone.

106. Serpentinite
•Color: Green, dark green, mottled.
•Texture: Fine to medium-grained, often smooth or greasy feel.
•Hardness: 3–5 (Mohs).
•Lustre: Greasy to silky.
•Density: 2.5–2.6 g/cm³.
•Porosity: Low.
•Fracture: Splintery to uneven.
•Specific Gravity: 2.5–2.6.
•Chemical Composition: Serpentine minerals (Mg₃Si₂O₅(OH)₄).
•Strength: 50–150 MPa (compressive).
•Durability: Moderate; can alter over time.
•Uses: Decorative stone, carving material.

108. Tests on Rocks
LLO 1: Appraise the rock testing procedure,
LLO 2: Assess the performance of rock

111. Uniaxial Compression Test on rocks (IS 9143- 1979
To find rock strength directly
Cylindrical rock specimens are tested in Universal Testing Machine (UTM)
Specimen
Length-to-width ratio = 2 to 2.5
Diameter = 454mm or 47mm
Should be flat, smooth and parallel ends cut perpendicular to the cylinder axis

114. Direct Uniaxial Compressive Strength (UCS) testing on rocks is often not possible in
many site and lab situations because of several practical limitations:
•Sample Preparation Requirements
UCS testing needs perfectly shaped right-cylindrical specimens with:
Length-to-diameter ratio ≈ 2:1
Smooth, flat, parallel end faces (perpendicular to axis)
Many rock cores from drilling are broken, irregular, or too short to prepare to this standard.
•Equipment Limitations
UCS testing requires a large, rigid compression testing machine capable of applying high loads (hundreds of kN).
Portable field setups for UCS are not practical — it’s lab-based only.
•Time & Cost
Coring, trimming, and grinding to precise UCS specimen dimensions is time-consuming and costly.
When many samples are needed for classification, UCS preparation is inefficient.
•Fragile or Weathered Rocks
Weak, laminated, or fractured rock often breaks during preparation, making UCS specimens impossible to prepare.
Weathered rocks may crumble before testing.

116. •Limited Core Recovery
In some drilling projects, the recovered core lengths are too short for UCS
specimens — especially in fractured or jointed formations. Point Load Test can use
small or irregular pieces.
Why Use Point Load or Indirect Tests Instead?
•Point Load, Brazilian, and other indirect methods can:
•Be done on irregular or small specimens.
•Be carried out in the field or lab.
•Give quick, approximate UCS values through correlation.
•This is why IS 8764 and other standards recommend the Point Load Index as a
practical alternative for rock mass classification.

117. Point Load Strength Test -IS 8764 (1998)
•Purpose: To estimate the tensile strength and indirectly the uniaxial compressive
strength (UCS) of rocks. (approx. UCS = 20 to 25 × I
s(50)).
•Principle:
A rock specimen is loaded between two conical steel platens until failure. The
load is applied either on:
•Axial core (diametral)
•Core end (axial)
•Irregular lumps
•Specimen:
•Diameter: 30–100 mm
•Length-to-diameter ratio: ~1.0–1.5
•Irregular lumps allowed for field testing.
•Apparatus: Point load frame with
a hydraulic jack and load gauge.

118. Diametral core specimen
Axial core specimen Irregular lump specimen
Point Load Test apparatus

120. Testing is carried out at natural water content
Rock specimen is broken by applying concentrated load using conical
platens
Distance b/w specimen-platen contact points is recorded
Load is steadily increased and failure load is recorded
Test is not be used for weak rocks with unconfined compressive
strength < 25 MPa

121. Procedure:
•Measure D (distance between loading points)
and W (width).
•Place specimen correctly between platens.
•Apply load at a rate to cause failure in 10–60
seconds.
•Record failure load P.
•To Calculate Point Load Index:
•Minimum of 10 test specimens tested, find
average value.
•• Test can be conducted on dry or 2 days
soaked specimens.
••Point load Index I
s =
??????
??????
??????
••Anisotropic specimen: test along and across
the bedding plane
•Advantages: Portable, quick, works on irregular
specimens.
•Limitations: Accuracy depends on rock anisotropy and
moisture.
Different-sized specimens behave differently under load — larger specimens tend
to have lower measured strength due to scale effects. The correction normalizes
them to a common standard size.

122. Deformation behavior of rock under loading is verified by applying
compressive load until the core specimen fails by fracture
Test results are influenced by :-
Rate of loading → should be constant
Moisture content of specimen
Condition of two ends of specimen → should be planar and parallel
Inclined fissures, intrusions and other anomalies → cause premature failures

123. Splitting Tensile Strength Test (IS 10082)
Also called Brazilian Test
Used for intact rocks
Measures uniaxial tensile strength of rock
sample indirectly
Most fundamental test as tension is more
likely failure mode in many situations than
compression
❖The split tensile test,isan indirect method used to determine the tensile strength of rock specimens.
❖It involves applying a compressive force to a cylindrical rock sample, which induces tensile stress and
causes it to split along its diameter.
❖This method is widely used because it is simpler and less expensive than direct tensile tests.

124. Core specimens with L/D ratio b/w 2 and 2.5 is placed in compression testing
machine
Load platens are placed diametrically, across the specimen
Record maximum load (P) to fracture the specimen
Brazilian or Splitting Tensile Strength

125. Rock Quality Designation (RQD)- IS 11315 (Part 11).
RQD → %age of intact rock retrieved from borehole
To predict tunneling conditions and support requirements
Enables to identify potential problems related to bearing capacity,
settlement, erosion or sliding in rock foundations
Indicate rock quality in quarries for concrete aggregate and rockfill
RQD = sum of all pieces of intact rock core equal to or greater than
100 mm divided by the total length of the core run

126. Rock Quality Designation (RQD)is a modified core recovery percentage in
which the lengths of all sound rock core pieces over 100 mm (in length) are
summed and divided by the length of the core run.
Pieces of core that are not hard and sound should not be included in the RQD
evaluation even if they are at least 100 mm in length.
High-quality rock has an RQD of more than 75%, low quality of less
than 50%. Rock quality designation (RQD) has several definitions.
Rock Quality Designation (RQD)

129. A borehole core of 1.5 m length was recovered during drilling. The lengths of the
sound (intact) core pieces greater than 100 mm are listed below:
•120 mm, 180 mm, 90 mm, 250 mm, 160 mm, 80 mm, 210 mm
•Identify which core pieces should be considered for RQD.
•Calculate the RQD value.
•Classify the rock mass quality based on RQD.
Practice Problem 1

130. Solution :
1.Only pieces ≥ 100 mm are counted.
⇒ Valid pieces = 120, 180, 250, 160, 210 mm (Ignore 90 mm and 80 mm).
2.Total length of valid pieces = 120+180+250+160+210=920mm=0.92m
120 + 180 + 250 + 160 + 210 = 920 = 0.92m
RQD = Sumofcorepieces≥100mm / Totalcorerun length×100
RQD=0.92/1.5×100=61.3%
Classification (IS 11315 / Deere):
1.90–100% → Excellent
2.75–90% → Good
3.50–75% → Fair
4.25–50% → Poor
5.<25% → Very Poor
Rock Mass Quality: Fair

131. Objective
To determine the resistance of rock against disintegration when subjected to two
standard cycles of drying and wetting.
It is especially useful for shales, mudstones, claystones, laterites, and other weak
rocks.
Slake Durability Test (as per IS 10050:1981)
Slake Durability Apparatus:
1.A drum (140 mm dia × 100 mm length) made of standard mesh (2 mm aperture).
2.The drum is mounted horizontally on shafts inside a water bath.
3.Rotates at 20 rpm for 10 minutes.

132. Defines the weathering behavior of rocks
To determine the durability of shale, weak or soft rocks
Useful to determine disintegration nature of rocks when subjected to drying and
wetting conditions along with movement
Rock fragments of known weight are placed in a drum fabricated with 2.0 mm
square mesh wire cloth
Drum is partially submerged in distilled water to promote wetting

133. Specimens and the drum are dried at the end of the rotation cycle and weighed
After 2 cycles, weight loss and the shape and size of the remaining rock
fragments are recorded

134. Rotating Drum Assembly and Setup of Slake Durability Equipment

135. Procedure
1. Dry the sample to constant mass by placing it in oven, maintained at a temp of 105±5
0
C. Place the
sample in the drum of the machine and record the weight of sample plus drum as ‘A’.
2.Fit the lid with the drum; mount the drum in the trough.
3.Fill the trough with slaking fluid to a level 20 mm below the drum axis. Rotate the drum at 20
rev/min for a period of 10 minutes.
4.Remove the drum from trough and remove the lid from the drum.
5.Dry the drum plus retained portion of the sample in an oven maintained at a temp of 105±5
0
C.
6.Record the weight of drum plus retained portion of the sample as ‘B’.
7.Repeat the steps from 2 to 5 for a further period of 10 minutes. Record the weight of drum plus
retained portion of sample as ‘C’.
8.Clean the drum and record its weight as ‘D’.
The slake durability index (2
nd
cycle) is calculated as percentage ratio of final to
initial dry sample weight as follows.
Slake durability index (%),I
d2= ((C-D)/(A-D))*100

136. Slake Durability
Index (Id2)
Durability Grade Description
0–25% I Very Low durability
25–50% II Low durability
50–75% III Medium durability
75–85% IV High durability
85–100% V Very High durability

137. Degree of Rock Mass Weathering
Degrees of rock mass weathering (BS5930, 1981)

138. A rock sample is tested using the standard slake-durability drum (20 rpm, 10 min per cycle). Ten
lumps (~40–60 g each) are oven-dried at 105 ± 5 °C, cooled, and weighed. Initial oven-dry weight
before testing: W1=498.6g
Weight retained in drum after Cycle 1 (oven-dried again): W2=431.5g
Weight retained in drum after Cycle 2 (oven-dried again): W3=402.8g
1.Compute the first-cycle slake durability index ??????
??????2
2.Compute the second-cycle slake durability index ??????
??????2
3.Classify the rock’s durability using ??????
??????2.
Practice Problem 2
Result: I
d1 = 86.5%% I
d2= 80.8% → High durability (Grade IV).

139. Problem 1 — Core (D=50 mm), load in kN
A diametral test on a 50 mm core fails at 8 kN.
Find: I
s, I
s(50) and UCS (use K=24).
Practice Problem 3

140. Points to remember
Answer: I
s=3.20 MPa; Is(50)=3.20 MPa; UCS = 76.8 MPa

141. Practice Problem 4