Sedimentary Rock & Igneous Rock Notes

1. SEDIMENTARY ROCK
1. Describe the formation of sedimentary rock.
Ans- Sedimentary rocks form from the accumulation of sediment at earth’s surface.
The Sedimentary Rocks Formed in four different stages:
– Weathering
– Transportation
– Deposition
– Consolidation
WEATHERING
– Mechanical weathering disintegrates a pre-existing rock into smaller fragments; Chemical weathering acting
on these fragments rearranges these elements into new minerals.
– Mechanical weathering is done by air, water action, temperature changes, expansion due to freezing of water
etc.
TRANSPORTATION
– Generally transported in large amount by running water (rivers), moving ice (glaciers) or wind.
– The fragmented particles are carried by water in suspension and the products that are dissolved in water are
carried in solution.
DEPOSITION
– The transportation of the weathered products continues as long as the velocity of the transporting medium
remains unchecked.
– But when these products are brought at rest into big water bodies like oceans and lakes, their deposition will
start.
– The coarser and heavier pieces will settle first, followed by lighter and finer particles.
– The weathered products carried in solution may precipitate out at a later stage, which may form a separate
layer on deposition.
COMPACTION
– As the deposition of sediment continues, it automatically goes on compacting and consolidating due to it’s
own weight with the squeezing out of water.
– Fine grained sedimentary deposits such as shale and siltstone gets effectively lithified by compaction.
2. What is lithification ?
Ans- The transformation of loosely deposited sediments into rock is called lithification.
3. Write a short note on cementation ?
Ans- Water soluble materials such as calcite, silica, iron oxides, dolomites, clay etc. are deposited by ground
water, between the various grains of the deposited sediment, thus bonding them together. This process is
called cementation. The strength, toughness and other characteristics achieved by the sedimentary rock so
formed, will considerably depend upon the material forming the bond.
Silica produces the toughest rocks.
Iron oxide gives red or yellow color to the rocks
Clay makes poor rocks and may possess grey or green-grey color.
4. Describe the classification of sedimentary rocks.
Ans- Sedimentary rocks form from the accumulation of sediment at earth’s surface.
Classification- 1.CLASTIC 2.CHEMICAL 3.ORGANIC
• Clastic - Sedimentary rocks are classified based on their texture and composition. Detrital sediment
has a clastic (broken) texture. Chemical and organic sediments have a non-clastic texture, and are
classified based solely on their composition.

2. Clastic rocks are named for their grain size and shape. There are 3 types:
– Coarse-grained (>2 mm) rocks with rounded grains are called conglomerate. If the coarse-grains are angular, the
rocks are called breccia.
– Medium-grained (1/16 mm to 2mm) rocks are usually called sandstone.
– Fine-grained (<1/16 mm) rocks are generally called mudrocks. They include siltstone and shale.
• Non-clastic Texture - Non-clastic rocks have chemical or organic origins. Names of non-clastic
rocks are based on their compositions. Microcrystalline quartz is called chert. The red variety of
chert is called jasper. Dark gray to black chert is called flint.
• Non-clastic Texture (contd.) - The carbon-rich rock formed from ancient plant material is called
coal.
5. Write Down The structure of Sedimentary rocks.
Ans- There are 5 types Structure –
1. MECHANICAL STRUCTURES
2. Stratification or Bedding
3. Lamination and Cross lamination
4. Ripple marks
5. Rain marks
6. Joints and Cracks
MECHANICAL STRUCTURES: Mechanical structures include all those structures that have been developed in
sedimentary rocks due to some physical processes operating at the time of deposition of sediments.
Stratification or Bedding: • Sedimentary rocks are generally found quite definitely arranged in layers or strata.
• These strata are horizontal at the time of formation but may get folded.
• These layers (beds) of sedimentary rocks represent their age of deposition over very long
periods. Naturally, the oldest layer will be at the bottom.
• The agents of transportation sort out the sediment during it’s transportation, according
to size, weight, and shape of the particles.
Lamination and Cross lamination: • When the thickness of a bed is very small (less than 1 cm), it is called a lamina.
• The deposit with a lamina is said to be laminated.
• Laminae may be parallel to the bedding planes or at an angle to them.
Ripple Marks: • Ripple marks are the symmetrical or unsymmetrical undulations that may be seen on some
sedimentary deposits.
• These are caused by winds or waves, during the deposition of sediments in a shallow water
environment.
Rain Marks- The marks left by the falling rain on loose sediments, are called rain prints or rain marks.
Joints & Cracks- • In unconsolidated or partially consolidated sediment deposits, joints often develop
because of shrinkage due to water loss, compaction and settlements.
• In coarser sediments, these joints don’t show any gaps. However, in clays, wide cracks with
gaps may open out.

3. Igneous Rock
1. Describe The Rock Cycle.
Ans- All rock on earth are locked into a system of cycling and recycling know as the rock cycle.
Weathering
Simply put, weathering is a process of breaking down rocks into smaller and smaller particles without any
transporting agents at play. Factors like temperature extremities, biological involvement of nature and water
plays the main role.
It can be broken down into chemical, physical and biological influencing agents.
Erosion and Transport
Erosion too is the natural process of breaking down rocks into sand-like particles. The only difference
between weathering to erosion is the presence of agents like water and wind. In the previous one, water was
only present as a factor for reactions to take place while in erosion, it acts as a transporting agent too.
Various events like attrition, abrasion and solution, wind transportation give rise to caves, new tributaries,
and cracks in big rocks while wind transportation gives rise to thinned down rocks.
Deposition of Sediment
Sediment is the constant deposition or settling down of small particles of sand, pebbles, etc. that is broken
down from rocks. It is usually done by-
• Wind and water- Water in the rivers and glaciers from mountains slowly erode sand particles and
create layers of sediments.
• Biological Influence- Living organisms die and get sedimented under great pressure to form rocks.
• Evaporation- Chemicals like CaCO3 and NaCl are sedimented in troughs and seashores to create
limestones and rock salts respectively.
Burial and Compaction
The next step to the process of sedimentation is burial and Compaction. The process is very simple. Once
the sand particles are sedimented, they create layers which are soon covered by another layer of new
sediments and the process goes on. This gives rise to pressure on the sedimented layers below. Meanwhile,
the mine

4. ls in the water act as a slow cohesive agent between the particles. Thus, soft layers turn into solid rocks with
minerals inside.
Crystallization of Magma
Magma is basically lava that remains dormant inside the volcanoes. Magma is the liquid form of rocks under
great pressure and temperature due to heat from the earth core. Magma can be both sticky or less viscous. It
depends on factors like temperature and amount of dissolved gas.
The less viscous erupt and form porous rocks with fine grains while the more viscous ones form solid rocks
with distorted grains.
Melting
The reverse of the previous process is melting. As soon as the rocks reach the bottom of the earth, the more
the temperature rises and so does the pressure. Soon, they melt and give rise to melted rocks called lava.
This, in turn, is erupted only to cool down at the surface to form rocks. Some rocks do not erupt and are
forced to change characteristics to give rise to new forms of rock.
Uplift
The process of forming a crust of earth upwards due to natural forces causing movements in the tectonic
plates is called uplifting. This is how mountains rise higher while new islands come up in the middle of the
oceans.
Deformation and Metamorphism
The constant pressure and sudden movements put some sedimentary and igneous rocks under great pressure.
Such forces can create folds or fissures among the rocks and among all these events, rocks deform to create
metamorphic rocks. Deformation basically means folding and faulting of rocks. This is caused by
compression and tension.
2. Write Down the composition of igneous rock.
Ans-

5. 3. Write down the six families of silicate mierals.
Ans- pyroxenes [augite]
amphiboles [hornblende]
micas [muscovite, biotite]
feldspars [orthoclase, albite, anorthite]
Olivines [(Mg,Fe)2SiO4]
silica minerals [quartz]
4. Define Lava
Ans- Molten rock that issues from a volcano or from a fissure in the surface of a planet (such as earth) or
moon.
5. Write a short note on pyroclasts.
Ans- Pyroclastic flows contain a high-density mix of hot lava blocks, pumice, ash and volcanic gas. They
move at very high speed down volcanic slopes, typically following valleys. In some cases, instead of flowing
from the volcano as lava, the magma is exploded into the air by the rapid escape of the gases from within it.
The fragments produced by explosive activity are known collectively as pyroclasts.
6. Write a short note on obsidian.
Ans- Obsidian is an igneous rock that cooled very quickly at the Earth’s surface and displays a glassy texture
and conchoidal fracture.
7. Define Pegmatite.
Ans- Pegmatites are extreme igneous rocks that form during the final stage of a magma's crystallization.
They are extreme because they contain exceptionally large crystals and they sometimes contain minerals
that are rarely found in other types of rocks.
8. Define vesicules.
Ans- When gas trapped in the magma cools quickly, it forms bubbles that remain after cooling and
solidification; the resulting void spaces in the rock are termed vesicules.
9. Write the uses of granite.
Ans- It is the world’s toughest substance. It has been used for thousands of years. Apart from using it for
building monuments, it is also used in curling balls and gym walls for mountain climbing training.
Below are the granite uses in different forms:
• Building monuments
• Granite used in jewelry
• Granite used in fireplace mantle and floor
• Granite used in bathroom skins, shelves, tabletops, basins
10. Describe the different of physical geology & historical geology ?
Ans- The scope of geology is so broad that it can be divided into two divisions.
Physical geology Historical geology
1. Physical geology deals with the Earths’s composition,
structure, the movement within and upon the Earth’s
Crust and the geological process by which the earth’s
surface has been changed.
1. Historical geology examines the origin and evolution
of our planet through time and also its inhabitants.
2. Branches- Physical Geology, Mineralogy, Petrology,
Structural geology, Geomorphology, Economic geology
2. Branches- Stratigraphy, Palaeontology,
Palaeogeography
3. Physical geology deals with present-day problems, like
rock formation, earthquakes, volcanoes, and pollution
issues, among others.
3. Historical geology looks at preserved evidence of past
geologic events. This includes interpreting fossil records
and rock records to better understand events that took
place in the past.
4. Earth's physical processes and features 4. Earth's history
5. Present day and recent past 5. Entire history of the Earth

6. 6. Observations of current processes, experiments, and
modeling
6. Study of fossils, rock layers, and other preserved
evidence
7. Understanding natural hazards, predicting climate
change, and managing natural resources
8. Understanding the evolution of life, the formation of
mountains, and the history of the Earth
11. Describe the Important of geology in Civil Engineering?
Ans- Geology is the study of the Earth's physical structure and history, and it is essential for civil engineering.
Civil engineers design and build infrastructure that interacts with the Earth's surface, so they need to
understand the geology of the area where they are working.
Here are some of the ways that geology is important in civil engineering:
• Site selection: Civil engineers need to consider the geology of a site when selecting it for a project. For
example, they need to make sure that the site is stable enough to support the weight of the structure that they
are building. They also need to make sure that the site is not in a floodplain or other area that is prone to
natural disasters.
• Foundation design: The foundation of a structure is the part that connects it to the ground. The type of
foundation that is used depends on the geology of the site. For example, if the site is on soft soil, a deeper
foundation may be needed.
• Slope stability: Civil engineers need to make sure that slopes are stable enough to support the weight of
structures that are built on them. They may need to take steps to stabilize slopes, such as installing retaining
walls or planting vegetation.
• Geotechnical engineering: Geotechnical engineering is a branch of civil engineering that deals with the
engineering properties of soil and rock. Civil engineers who specialize in geotechnical engineering use their
knowledge of geology to design and build structures that are safe and stable.
• Natural hazards: Civil engineers need to be aware of the natural hazards that can occur in the area where
they are working. They need to design structures that can withstand these hazards, and they may need to take
steps to mitigate the effects of these hazards.
• Drainage design: Civil engineers use geology to design drainage systems for roads, bridges, and other
structures. They need to consider the amount of rainfall and runoff in the area, the type of soil, and the slope
of the ground.
• Environmental impact assessment: Civil engineers use geology to assess the environmental impact of a
proposed project. They need to consider the presence of endangered species, the quality of groundwater, and
the potential for soil erosion.
12. What is geology? Scope is geology? Importance of geology.
Ans- Geology = Geo (earth) + Logos (discourse)
Geology is the study of the earth, the material of which it is made, the structure of those materials and
the process acting upon them over time.
The scope of geology is so broad that it can be divided into two divisions.
1. Physical geology deals with the Earths’s composition, structure, the movement within and upon the Earth’s
Crust and the geological process by which the earth’s surface has been changed.
2. Historical geology examines the origin and evolution of our planet through time and also its inhabitants.
1. Geology provides a systematic knowledge of construction materials, their structure and properties.
2. The knowledge of Erosion, Transportation and Deposition (ETD) by surface water helps in soil
conservation, river control, coastal and harbor works.
3. The knowledge about the nature of the rocks is very necessary in tunneling, constructing roads and in
determining the stability of cuts and slopes. Thus, geology helps in civil engineering.
4. The foundation problems of dams, bridges and buildings are directly related with geology of the area
where they are to be built.
5. The knowledge of ground water is necessary in connection with excavation works, water supply,
irrigation and many other purposes.
6. Geological maps and sections help considerably in planning many engineering projects.

7. 7. If the geological features like faults, joints, beds, folds, channels are found, they have to be suitably
treated. Hence, the stability of the structure is greatly increased.
8. Pre-geological survey of the area concerned reduces the cost of engineering work.
13. What is mineral? Write down the characteristic of a mineral.
Ans- An inorganic element or compound in its natural state is called mineral.
1. Naturally occurring: Minerals are found in nature and are not man-made.
2. Inorganic: Minerals do not contain carbon and are not made from living organisms.
3. Solid: Minerals are solids at room temperature and pressure.
4. Crystalline: Minerals have a regular internal structure, with atoms arranged in a repeating pattern.
5. Definite chemical composition: Minerals have a specific chemical composition, which means that they
contain the same elements in the same proportions.
14. Describe the physical properties of mineral.
Ans- The physical properties of minerals refer to the properties of a mineral that can be observed without
changing the chemical composition of the mineral. Some of the most important physical properties of
minerals include:
• Hardness: This is a measure of how resistant a mineral is to scratching. It is measured on the Mohs scale of
hardness, which ranges from 1 (softest) to 10 (hardest). Quartz is a mineral with a hardness of 7, while talc is
a mineral with a hardness of 1.
• Cleavage: This is the tendency of a mineral to break along smooth, flat surfaces. Some minerals, such as
mica, have perfect cleavage, meaning they break along smooth, flat surfaces in any direction. Other minerals,
such as calcite, have only one direction of cleavage.
• Fracture: This is the way a mineral breaks when it is not along a cleavage plane. Some minerals, such as
quartz, have a conchoidal fracture, which means they break in a smooth, curved surface that resembles the
shape of a conch shell. Other minerals, such as feldspar, have an irregular fracture, which means they break in
an uneven, jagged surface.
• Color: The color of a mineral can be caused by impurities, by the way the mineral reflects light, or by the
mineral's chemical composition. Some minerals, such as pyrite, have a characteristic color. Other minerals,
such as feldspar, can vary in color depending on their impurities.
• Streak: The streak of a mineral is the color it leaves when it is rubbed against a streak plate. The streak is
often different from the color of the mineral itself. For example, the mineral hematite is red, but it has a black
streak.
• Lustre: This is the way a mineral reflects light. Some minerals, such as diamond, have a metallic luster. Other
minerals, such as quartz, have a glassy luster.
• Specific gravity: This is the ratio of the weight of a mineral to the weight of an equal volume of water.
Specific gravity is a useful property for identifying minerals with similar densities.
• Tenacity: This is a measure of how resistant a mineral is to breaking, bending, or deforming. Minerals can be
brittle, malleable, ductile, or elastic.
These are just some of the physical properties of minerals. By observing these properties, geologists can identify and
classify minerals.
15. What is crystallography. Draw crystals systems.
Ans- Crystallography is the scientific study of crystals, their internal structure, and their physical properties.

8. 16. Write a short note of tenacity?
Ans- Tenacity is the resistance of a mineral to breaking, crushing, or bending. It is a measure of a mineral's
toughness and its ability to withstand deformation. There are five main types of tenacity:
Brittleness, Sectility, Malleability, Flexibility, Elasticity.
17. Write down the difference between color & streak.
Ans-
Color Streak
Color is the visible property of a mineral that is
determined by the wavelengths of light that it
reflects.
Streak is the color of a mineral in its powdered
form.
The color of a mineral can vary depending on its
chemical composition, crystal structure, and
impurities.
It is determined by the mineral's chemical
composition and crystal structure.
Hematite Black Cherry-red
Chromites Greenish-black Greenish-brown
Pyrite Brass-yellow Black