Petrology for Civil Engineering

Why is Petrology important for civil engineering ?
Petrology is the most important branch of geology from
civil engineering point of view.
Based on their suitability, rocks can be utilized as
foundation for dams, tunnels, and other construction
materials.
The composition and texture of rocks primarily
contribute to their strength and durability.

Why is Petrology important for civil engineering ?
Petrology provides an opportunity to interpret the
physical properties of individual rocks like: Texture,
Structures.
Rocks and Mineral may change between igneous,
sedimentary and metamorphic. Petrology is important
because it tells about earth history.
It is key to the discovery and development of mineral
resources and fundamental principles and lessons
learned from petrology have application in modern
industry.

Stone :
1. A small, Hard solid, moveable, non-metallic mineral matter.
Stone is simply a little piece or pebble that may be held in one's hand.
2. Rocks and stones are made of the same substance.
Rocks are formed from smaller stones. Rocks are huge pieces of stone
that are tough to carry in one's hand.
Mineral: Mineral are natural occurring inorganic substance of
fixed chemical composition.
Minerals are the smallest geological unit forming crust.
Rock :
Rock are aggregates of minerals, whether consolidated or
unconsolidated, that forms part of the Earth's crust..

DIFFERENT TYPES OF ROCKS
Based on the chemical composition, formation, origin the rock can
be classified into three (03) classes.
(1) Igneous rock
(2) Sedimentary rock
(3) Metamorphic Rock

(1) Igneous rocks are developed from originally hot, molten materials
through the processes of cooling and crystallization.

IMPORTANT IGNEOUS ROCKS
A. Granite is a plutonic, light colored, equi-granular textured igneous rocks.
Composition: Quartz, Feldspar, Mica, Hornblende, Hypersthene.
Texture: It is coarse grained, holocrystalline and equi-granular rocks.
Types: Muscovite-granite, biotite-granite, Muscovite biotite-granite,
hornblende – granite, augite-granite and tourmaline – granite.
Occurrence : It is most commonly distributed igneous rocks in the crust.
It occur as deep-sheeted intrusive body. E.g.: sills, dyke, bosses, stocks, batholiths.
Use: Architectural and massive construction
B. Gabbro,
C. Diorite,
D. Basalt

A. Granite is a plutonic, light colored, equi-granular textured igneous rocks.
B. Basalt is a volcanic , dark coloured, fine grained, aphaneritic textured igneous rock

(1) Igneous rock are developed from originally hot, molten materials
(3) Metamorphic Rock

IMPORTANT SEDIMENTARY ROCKS
• Conglomerate
• Sandstone
• Shale
• Lime Stone

• Conglomerate
• Sandstone
• Shale
• Lime Stone
Conglomerate are rudaceous sedimentary rocks with an
elastic character. They are made up of spherical shaped of
varying sizes, but mostly larger than 2mm cemented
together, bonded together in a clayey matrix.
Based on Grain Size the Conglomerate can be classified in to:
Boulder (gravel > 256mm)
Cobble (gravel 64-256 mm)
Pebble (gravel 2 – 64 mm)
They consist of rounded fragments of various sizes but
generally above 2mm in a clayey matrix.
Based on Source, conglomerate can be classified in to:
Basal conglomerates
Glacial conglomerates
Volcanic conglomerates

• Conglomerate
• Sandstone : Sand size grains deposited in variety of environment,
shape rounded to angular shaped related to distance or
time of transport.
• Shale
• Lime Stone

• Conglomerate
• Lime Stone: Limestone is the most
common chemical sedimentary rocks
and is composed of the mineral calcite
limestone commonly contain fossils
of marine organism.
• Shale
• Sandstone

(1) Igneous rock are developed from originally hot, molten
materials through the processes of cooling and crystallization.
(3) Metamorphic Rock :
The physical and chemical transformation of solid rocks that
changes their texture, structure, and mineral content in reaction
to changes in their ambient conditions within the Earth.
These are pre-existing igneous and sedimentary rocks that have
had their texture, structure, and mineral content modified by
physical and chemical processes. Physical modifications include
crushing of grain, recrystallization, and grain interlocking.

IMPORTANT METAMORPHIC ROCKS
• Quartzite
• Marble
• Slate
• Phyllite
• Schist
• Gneiss

• Quartzite
• Marble
• Slate
• Phyllite
• Schist
• Gneiss
Quartzite is a granular metamorphic rock composed
chiefly of quartz grains. It is a mixture of Mica
Feldspars, Garnet and some amphiboles. The rock is
generally very hard strong, dense and uniformly
grained. it uses in building and roads construction.

• Quartzite
• Marble
• Slate
• Phyllite
• Schist
• Gneiss
Marbles are composed chiefly of recrystallized calcite.
Small amount of many other granular minerals like
olivine, serpentine, garnet and some amphiboles are
also present in many varieties. Marbles are commonly
used in building construction in the form of blocks,
slabs, arches and as chips for flooring. Marble is mostly
utilized for decorative and ornamental purposes.

• Quartzite
• Marble
• Slate
• Phyllite
• Schist
• Gneiss
MARBLE

• Quartzite
• Marble
• Slate
• Phyllite
• Schist
• Gneiss
Slate is an extremely fine – grained metamorphic rock
characterized by a slaty cleavage. It is composed of
Micas, Chlorite, Quartz, Feldspar, oxides of iron and
many other minerals all of which cannot be easily
identified even under microscope because of their fine
grain size.
Slate is used as a roofing material in the area. Because
of its low crushing strength and slaty cleavage, it
cannot be used as a building stone or road stone.

• Quartzite
• Marble
• Slate
• Phyllite
• Schist
• Gneiss
PHYLLITE is a metamorphic rock with fine to medium
grain and a complex silicate composition. Phyllites are
predominantly constituted of chloride, muscovite, and
quartz grains, all of which are in excellent shape and can
be seen with a hand lenses. This is, in fact, the major
contrast between slates and phyllites. Phyllites form
naturally as a result of dynamo-thermal metamorphism of
clay-bearing rocks like shale.

• Quartzite
• Marble
• Slate
• Phyllite
• Schist
• Gneiss
Schists are massively crystalline metamorphic rocks with a
distinctive schistose structure. Micas, Chloride, Talc,
Hornblende, Tremolite, Garnet, and Kyanite are all common
schist components. Schists are typically formed through
dynamo thermal metamorphism.
Ex: muscovite schist, biotite schist and tourmaline schist etc.

Gneiss is typically formed as a result of advanced
metamorphism of a variety of parent rocks, such as
sandstone. Gneisses have more feldspar and quartz than
schists. Gneiss variations that are compact, dense, and
massive are utilised as building and road stones.
• Quartzite
• Marble
• Slate
• Phyllite
• Schist
• Gneiss

• Quartzite
• Marble
• Slate
• Phyllite
• Schist
• Gneiss
GNEISS

• Quartzite
• Marble
• Slate
• Phyllite
• Schist
• Gneiss
ZOOMED PART

Igneous Rocks, Forms, Structures and Textures
Form of Concordant Body : Intrusive body runs parallel to the
structures of country rock without cutting or penetrating.
Concordant igneous rock are Sill, Laccolith, Lopolithic, Phacolith
Form discordant Body: Intrusive igneous rock cut across the
structures of the country rocks.
Discordant igneous rock are dyke, batholith

Igneous Rocks- Forms, Structures and Textures

Form Discordant Body: Intrusive igneous rock cut across the
structures of the country rocks.
Discordant igneous rock are dyke, batholith, Joints

Igneous Rocks- Structures
Pillow Lava is formed by submarine eruptions of basaltic magma whereby
the exterior chills and crystallizes rapidly against cold seawater at around 5
degree Celsius. The outside layer will have glassy texture with vesicle.

Igneous Rocks- Structures
Blocky Lava: is less mobile i.e. more viscous and has a
Rough and irregular surface. Vesicles are few and
irregular in shape

Sedimentary Rocks: Forms, Structures and Textures

Classification of Sandstone by Pettijohn (1972)

Metamorphic Rocks: Factors controlling metamorphism,
Textures and Structures of Metamorphic rocks

Diagram showing structural and fabric
element at all scale

Relict textures are textures inherited from the original rock type,
and which have survived metamorphism

Petrology for Civil Engineering

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