Rocks: ICSE Class 9 Geography solution

Summary

Rocks are solid natural materials found in the Earth’s crust, made up of different mineral elements. Unlike minerals, which have a specific chemical structure, rocks are mixtures and don’t have a definite chemical composition. The most common mineral elements in the Earth’s crust include silicon, aluminum, iron, and calcium.

There are three main families of rocks, grouped by how they were formed: Igneous, Sedimentary, and Metamorphic. Igneous rocks are created when hot, molten rock called magma cools down and becomes solid. If magma cools slowly deep inside the Earth, it forms intrusive rocks like granite, which have large crystals. If lava (magma that reaches the surface) cools quickly outside, it forms extrusive rocks like basalt, with small crystals. Igneous rocks are generally hard, crystalline, and don’t form in layers. They are often called primary rocks because they form the basis for other rock types.

Sedimentary rocks are formed from small pieces of other rocks, or the remains of plants and animals. These pieces, called sediments, are carried by wind, water, or ice and settle down in layers. Over a long time, the weight of the layers above squeezes the lower layers (compaction), and minerals dissolved in water act like cement to glue the sediments together (cementation). This whole process is called lithification. Sandstone, shale, and limestone are examples. Sedimentary rocks often have visible layers and are the only type that can contain fossils. They can be formed from broken rock fragments, from chemicals left behind when water evaporates, or from the remains of living things like shells or plants.

Metamorphic rocks are rocks that have changed. They start as either igneous or sedimentary rocks, but deep within the Earth, intense heat and pressure transform them into new kinds of rock. This change, called metamorphism, alters their texture and the minerals they contain, often making them harder. For example, limestone can change into marble, and shale can turn into slate. These rocks often show signs of bending or folding due to the pressure.

Rocks are very important for many reasons. They break down over time to form soil, which plants need to grow. We use rocks to build houses, roads, and bridges. Rocks also contain valuable resources like metals (iron, gold) and energy sources like coal and petroleum (fossil fuels), which are often found in sedimentary rocks.

All rocks are part of a continuous process called the rock cycle. Igneous rocks can be weathered down into sediments, which then form sedimentary rocks. Both igneous and sedimentary rocks can be transformed by heat and pressure into metamorphic rocks. If any rock gets buried deep enough, it can melt back into magma, which then cools to form new igneous rocks. This cycle shows how rocks are constantly being changed and recycled over millions of years.

Textbook solutions (Morning Star/Total)

Multiple-Choice Questions

1. An aggregate of minerals, with no definite chemical composition, that forms more or less a definite unit of the earth’s crust:

(a) Rock
(b) Mineral
(c) Crust
(d) Metamorphosis

Answer: (a) Rock

2. The magma when forced upwards fills vertical cracks or fissures in existing rocks and it then hardens there to form __________

(a) Necks
(b) Sills
(c) Dykes
(d) Laccoliths

Answer: (c) Dykes

3. With reference to Intrusive Igneous Rocks which of the following is incorrect?

(a) Batholiths – deep-seated large deposits of igneous rocks like graphite.
(b) Hypobyssal Rocks – small rock deposits.
(c) Neck – plug at the top of a volcano.
(d) Dykes – large deposits of cooled magma on the earth’s surface.

Answer: (d) Dykes – large deposits of cooled magma on the earth’s surface.

4. The process that turns loose sediments into rocks:

(a) Compaction
(b) Lithification
(c) Cementation
(d) None of the above

Answer: (b) Lithification

5. The bonding together of compacted sediments by natural bonding materials such as calcium compounds, silica and iron:

(a) Compaction
(b) Lithification
(c) Cementation
(d) None of the above

Answer: (c) Cementation

6. Transported sediments get deposited in layers leading to increased pressure and temperature on the lower layers. Select the correct sequence of processes involved in the lithification of these sediments.

(a) Compaction – Evaporation – Cementation.
(b) Evaporation – Compaction – Cementation.
(c) Evaporation – Cementation – Compaction.
(d) Evaporation – Dehydration – Cementation.

Answer: (b) Evaporation – Compaction – Cementation.

7. Sam was working under a geologist. He lost his balance and dropped the bags containing igneous rocks and sedimentary rocks and the rocks got mixed. How would be separate them?

(a) Igneous rocks are hard.
(b) Igneous rocks are crystalline.
(c) Sedimentary rocks have strata showing layers.
(d) Sedimentary rocks are soft.

Answer: (c) Sedimentary rocks have strata showing layers.

8. The rocks like peat, lignite, bituminous and anthracite example of:

(a) Igneous rocks
(b) Mechanical rocks
(c) Metallic rocks
(d) Carbonaceous rocks

Answer: (d) Carbonaceous rocks

9. Rocks found on the bed of a lake corresponding to successive periods of deposition:

(a) Lacustrine
(b) Glacial
(c) Aeolian
(d) Riverine

Answer: (a) Lacustrine

10. Rocks formed with sand particles brought by winds.

(a) Glacial
(b) Marine
(c) Lacustrine
(d) Aeolian

Answer: (d) Aeolian

11. Rocks formed by the alluvial deposits brought by the flowing water of streams.

(a) Marine
(b) Glacial
(c) Riverine
(d) Aeolian

Answer: (c) Riverine

12. The alteration of the composition or structure of a rock by heat, pressure or other natural agency:

(a) Thermal Metamorphism
(b) Metamorphism
(c) Regional Metamorphism
(d) Dynamic Metamorphism

Answer: (b) Metamorphism

13. The transformation of the original rock takes place due to the influence of high temperature:

(a) Metamorphism
(b) Thermal Metamorphism
(c) Regional Metamorphism
(d) Dynamic Metamorphism

Answer: (b) Thermal Metamorphism

14. The transformation takes place mainly because of pressure at a great depth within earth’s crust:

(a) Thermal Metamorphism
(b) Metamorphism
(c) Regional Metamorphism
(d) Dynamic Metamorphism

Answer: (d) Dynamic Metamorphism

15. The transformation of rocks due to the pressure of overlying rocks and the intense heat caused by large-scale earth movements:

(a) Regional Metamorphism
(b) Thermal Metamorphism
(c) Metamorphism
(d) Dynamic Metamorphism

Answer: (a) Regional Metamorphism

16. The continuous process of transformation of old rocks into new ones:

(a) Metamorphism
(b) Rock flow
(c) Rock cycle
(d) Compactation

Answer: (c) Rock cycle

17. __________ are deep-seated intrusion of igneous rocks.

(a) Sills
(b) Dykes
(c) Laccoliths
(d) Batholiths

Answer: (d) Batholiths

Short Answer Questions

1. State two points of distinction between rocks and minerals.

Answer: Two points of distinction between rocks and minerals are:

Rocks are aggregates of mineral elements, whereas minerals are solid inorganic substances occurring naturally.
A rock has no definite chemical composition, whereas minerals have a definite chemical composition.

2. Name any three elements of the earth’s crust.

Answer: Three elements of the earth’s crust are silicon, aluminium, and iron.

3. Name three types of rocks.

Answer: Three chief types of rocks based on origin are Igneous, Sedimentary, and Metamorphic.

4. Give two differences between Extrusive Igneous and Intrusive Igneous rocks.

Answer: Two differences are:

Extrusive Igneous rocks are formed by the cooling of molten magma on the earth’s surface, whereas Intrusive Igneous rocks are formed when the magma solidifies within the earth’s crust.
Extrusive Igneous rocks are smooth, crystalline and fine grained, whereas Intrusive Igneous rocks cool slowly forming coarse textured, hard rocks with large crystals.

5. Name any two characteristics of Igneous Rocks.

Answer: Two characteristics of Igneous Rocks are:

They are hard and compact.
They are formed by solidification of molten magma.

6. State two characteristics of Basic Igneous Rocks.

Answer: Two characteristics of Basic Igneous Rocks are:

They have higher percentage of oxides of denser elements and silica content varies between 40 to 60 percent.
They are heavy and dark in colour.

7. Name two important landforms made by Igneous Rocks.

Answer: Two important landforms made by Igneous Rocks are Batholiths and Laccoliths. Alternatively, lava flows and lava plateaus are formed by extrusive igneous rocks.

8. What are Sills? Give an example.

Answer: Sills are formed when magma flows between layers of rocks horizontally and then hardens there. This layer of intrusive rock is called Sill. The text does not provide a specific rock type example for a Sill.

9. Which rocks are associated with ores of metals and which rocks are associated with fossil fuels?

Answer: Igneous rocks may be associated with ores of metals. Many metallic minerals such as gold and silver are found in metamorphic rocks. Sedimentary rocks, particularly organically formed ones termed as carbonaceous rocks like peat, lignite, bituminous and anthracite coal, are associated with fossil fuels.

10. Mention any two characteristics of Sedimentary Rocks.

Answer: Two characteristics of Sedimentary Rocks are:

Sedimentary rocks are formed from materials derived from other rocks. They may also have plant and animal remains and thus may contain fossils.
They are most widespread on the surface of the earth and constitute about 75 per cent of the surface area of the globe.

11. Name the rocks which are most widespread on the earth. Give two examples.

Answer: Sedimentary rocks are the most widespread on the surface of the earth. Two examples are sandstone and limestone.

12. Name the three stages of lithification of Sedimentary rocks.

Answer: Three processes are involved in turning the loose materials into hard rocks, which is called lithification. These stages are evaporation, compaction and cementation.

13. Name the types of Sedimentary rocks based on agents of formation.

Answer: Based on the agents of formation, sedimentary rocks are classified as:

(i) Riverine Rocks
(ii) Lacustrine Rocks
(iii) Glacial Rocks
(iv) Aeolian Rocks
(v) Marine Rocks

14. Which agents are responsible for deposition of sediments?

Answer: Agents responsible for the deposition of sediments include forces of gradation like rivers, glaciers, ocean waves, running water, moving glaciers, and wind. The forces of running water, winds, glaciers and ocean currents transport disintegrated material to lower levels or the sea where sediments accumulate in basins, lakes or ocean beds.

15. What are known as metamorphic rocks? Give two examples.

Answer: Metamorphic rocks are rocks formed by the change in the form of igneous or sedimentary rocks under the earth’s crust by temperature and pressure. Metamorphism refers to the alteration of the composition or structure of a rock by heat, pressure or other natural agency. The rocks were once igneous or sedimentary which underwent change through physical or chemical processes. Two examples are Marble (formed from Limestone) and Slate (formed from Shale).

16. Briefly define Mechanical Metamorphism.

Answer: Mechanical Metamorphism refers to the transformation of rocks primarily due to pressure at great depths within the Earth’s crust. This process, also called Dynamic Metamorphism, alters the rock’s structure without involving significant heat, causing minerals to realign and form new textures, such as foliation.

Distinguish Between the Following

1. Distinguish between Plutonic and Volcanic rocks.

Answer: Plutonic rocks are intrusive igneous rocks formed due to the slow cooling of magma at great depth, which leads to the formation of crystals of large size. Volcanic rocks are extrusive igneous rocks formed by the cooling of molten magma on the earth’s surface; the magma, brought to the surface through fissures or volcanic eruptions, solidifies to form rocks that are smooth, crystalline, and fine-grained. Basalt is a common volcanic rock.

2. Distinguish between Thermal and Dynamic Metamorphism.

Answer: Thermal Metamorphism occurs when the transformation of the original rock takes place due to the influence of high temperature, which may be from hot magma or friction of moving rock layers; for example, slate is formed from clay, and graphite from coal. Dynamic Metamorphism occurs when the transformation takes place mainly because of pressure at a great depth within the earth’s crust; chemically active hot gases passing through the rocks change their chemical composition, and minerals get arranged in a series of bands known as foliation.

3. Distinguish between Sills and Dykes.

Answer: Sills are formed when magma flows between layers of rocks horizontally and then hardens there; this layer of intrusive rock is called a Sill. Dykes are formed when magma is forced upwards, fills vertical cracks or fissures in existing rocks, and then hardens there.

4. Distinguish between Calcarious and Carbonacious rocks.

Answer: Calcarious Sedimentary Marine Rocks are formed by the deposition of shells and skeletons of sea organisms like corals, clams, and oysters, which live on the ocean floor and extract calcium carbonate from ocean water; chalk and limestone are examples. Carbonaceous Sedimentary Rocks are formed by sea plants which remain buried for a very long period; these long-preserved remains, known as fossils, are converted into the form of coal, lignite, and peat due to the pressure of overlying rocks on them. Rocks like peat, lignite, bituminous, and anthracite are also termed carbonaceous rocks.

5. Distinguish between Acid Igneous Rocks and Basic Igneous Rocks.

Answer: Acid Igneous Rocks have a silica content between 65 to 85 per cent and generally lack iron and magnesium; Granite is an example, made up of large crystals of quartz, feldspar, and mica. Basic Igneous Rocks have a higher percentage of oxides of denser elements, with silica content varying between 40 to 60 percent; they are heavy and dark in colour, with Basalt, dolerite, and gabro being typical examples

Structured Questions

1. (a) Distinguish between rocks and minerals.

Answer: The differences between rocks and minerals are as follows:

Rocks	Minerals
1. Rocks are aggregates of mineral elements.	1. Minerals are solid inorganic substances occurring naturally.
2. A rock has no definite chemical composition.	2. Minerals have a definite chemical composition.
3. Minerals are organised to form rocks.	3. Elements are organised to form compounds which are known as minerals.
4. Three chief types of rocks are Igneous, Sedimentary and Metamorphic.	4. Four chief mineral groups are silicates, carbonates, sulphides and metallic minerals.
5. Basalt, granite, sandstone, slate and quartz are some important types of rocks.	5. Iron, silicon, magnesium, nickel, calcium, potassium, sodium are abundant minerals of the earth.

1. (b) Describe how igneous rocks are formed. State their main characteristics.

Answer: Igneous rocks were formed due to cooling, solidification and crystallisation of hot molten material of the earth known as magma found at great depths in the interior of the earth. Since the igneous rocks were the first to be formed, they are called primary rocks. They form the basis of formation of other types of rocks.

The main characteristics of Igneous Rocks are:

They are hard and compact.
They are formed by solidification of molten magma.
They are granular and crystalline.
They are either fine grained, smooth and compact or may have large crystals with coarse texture.
The size of their crystals depends upon the rate of cooling of the molten material.
These rocks are less affected by chemical weathering because water does not percolate in these rocks.
Most of them consist of silicates.
They do not have layers. They are generally weathered by mechanical weathering.
Igneous rocks are associated with volcanic activity and are found mostly in volcanic regions.

1. (c) Give a reason for each of the following:

(i) Igneous rocks also called the primary rocks.
(ii) Igneous rocks are used by builders and sculptors.
(iii) Sedimentary rocks are called secondary rocks.

Answer: (i) Igneous rocks are called primary rocks because the igneous rocks were the first to be formed. They form the basis of formation of other types of rocks.

(ii) Igneous rocks are usually compact and are of interest to builders and sculptors. For example, granite is commonly used as a building material.

(iii) Sedimentary rocks are called secondary rocks because they are formed by the solidification of sediments of original igneous, sedimentary or metamorphic parent rocks.

1. (d) Define different types of igneous rocks on the basis of their chemical composition.

Answer: On the basis of their chemical composition, igneous rocks are classified into:

(i) Acid Igneous Rocks: These rocks have a silica content between 65 to 85 per cent. They generally lack in iron and magnesium. Granite is an acid igneous rock. It is made up of large crystals of quartz, feldspar and mica.
(ii) Basic Igneous Rocks: They have higher percentage of oxides of denser elements and silica content varies between 40 to 60 percent. It is heavy and dark in colour. Basalt, dolerite and gabro are typical examples of this group.

2. (a) How are sedimentary rocks formed?

Answer: Sedimentary rocks are formed when igneous rocks (or any exposed rock) are exposed on the surface of the earth, are broken down by weathering and carried away by forces of gradation like rivers, glaciers and ocean waves. They are then deposited as sediments in seas, lakes, streams, etc., over long periods. Subsequent layers are added and due to their own weight from above, the sediments get cemented together to form sedimentary rocks. They are formed by the solidification of sediments of original igneous, sedimentary or metamorphic parent rocks.

2. (b) Explain the formation of sedimentary rocks on the basis of agents of formation.

Answer: On the basis of agents of formation, sedimentary rocks are classified as follows:

(i) Riverine Rocks are formed by the alluvial deposits brought by the flowing water of streams.
(ii) Lacustrine Rocks are found on the bed of a lake corresponding to successive periods of deposition.
(iii) Glacial Rocks are formed by the glacial deposits in the form of debris or tills. The glaciers erode the surface and the sides of a valley and transport the eroded material. When the glacier melts, the debris brought by it is left behind in the form of moraines, which form glacial rocks, including boulders, gravels, sand, etc.
(iv) Aeolian Rocks are formed with sand particles brought by winds. The deposition of sand particles, one over the other, makes them hard and form sedimentary aeolian rocks. Loess is an important Aeolian deposit.
(v) Marine Rocks are formed at the ocean floor. These are of two types:
(a) Calcarious Sedimentary Marine Rocks: Formed by the deposition of shells and skeletons of sea organisms like corals, clams and oysters, which extract calcium carbonate from ocean water. Chalk and limestone are examples.
(b) Carbonaceous Sedimentary Rocks: Formed by sea plants which remain buried for a very long period. These long preserved remains are known as fossils and are converted into coal, lignite and peat due to pressure.

2. (c) Give a reason for each of the following:
(i) Mechanically formed sedimentary rocks are also termed as stratified rocks.
(ii) Rocks like peat, lignite and anthracite are called carbonaceous rocks.
(iii) Fossils are present in sedimentary rocks.

Answer: (i) Mechanically formed sedimentary rocks are known as Stratified Rocks because such rocks are formed in layers as sediments are gradually squeezed by the weight of overlying sediments and the lower layers harden to form rocks.

(ii) Rocks like peat, lignite, bituminous and anthracite are termed as carbonaceous rocks because they are organically formed rocks containing remains of dead plants which underwent changes after being submerged. In coal, the percentage of carbon is very high.

(iii) Fossils are present in sedimentary rocks because sedimentary rocks are formed from materials derived from other rocks and may also have plant and animal remains.

2. (d) What is metamorphism? What are its causes? Give an example of rocks formed by heat and pressure.

Answer: Metamorphism refers to the alteration of the composition or structure of a rock by heat, pressure or other natural agency. The rocks were once igneous or sedimentary which underwent change through physical or chemical processes.

The factors that take part in changing the form of rocks are temperature and pressure, or both. Since rocks are composed of minerals, these may change their composition and texture under great pressure and temperature.

Examples of rocks formed by heat and pressure include marble formed from limestone, and slate formed from clay or shale. Graphite is formed from coal due to heat. Quartzite is formed from sandstone.

3. (a) State the chief characteristics of metamorphic rocks.

Answer: The chief characteristics of Metamorphic Rocks are:

They are harder and more compact than their original form. For example marble made from limestone is harder than limestone.
Most of them are impermeable – they do not allow water to percolate through them.
They do not have fossils as fossils in sedimentary rocks are destroyed during the formation of metamorphic rocks.
Metamorphic rocks are formed due to change in texture and composition of the pre-existing rocks.
New minerals are formed during the process of metamorphism.

3. (b) State the economic significance of rocks.

Answer: The economic significance of rocks includes:

Like minerals, rocks are of great resource value, some directly and some as constituents of minerals.
Soils are derived from weathering of rocks.
Almost all types of building materials used for paving roads, floors or building walls of houses or various other structures including bridges come from rocks.
Rocks are a source of precious metals like gold, silver, platinum, etc.
Apart from minerals and fossil fuels, even rock wastes have now been used in manufacturing various articles.
Many metallic minerals such as gold and silver are found in metamorphic rocks.

3. (c) What is Rock Cycle? How does it keep the earth young?

Answer: The Rock Cycle is the continuous process of transformation of old rocks into new ones. The cycle may also pass through the process of formation of sedimentary, metamorphic and igneous rocks.

In the operation of the rock cycle, the earth is kept young and movements of adjustments specially through horizontal flow or convection currents maintain the balance between various elements of the earth like oceans and continents.

3. (d) Draw a well labelled diagram of Rock Cycle.

Answer: For the diagram, see Fig. 6.12 (Morning Star/Total) or see here.

Thinking Skills

1. The stone tools were quite significant in the growth and development of human civilisation. Are the rocks still important to humans today? Give reasons to support your answer.

Answer: Yes, rocks continue to play a crucial role in modern human life. They are a primary source of construction materials such as granite, limestone and marble, used in buildings, roads and monuments. Rocks also contain valuable minerals and fossil fuels essential for energy production, manufacturing, and technology. Furthermore, soil—vital for agriculture—is derived from the weathering of rocks. Thus, rocks remain indispensable in daily life and economic development.

2. Do you think the minerals in a rock provide an important clue about how the rock was formed? Give reasons to support your answer.

Answer: Yes, the minerals present in a rock offer significant clues about its origin and history. For example, igneous rocks contain minerals like quartz and feldspar, which form from the cooling of molten magma. Sedimentary rocks may include calcite or clay minerals, indicating deposition from water or the remains of organisms. Metamorphic rocks often show new mineral formations like garnet or mica, suggesting exposure to high pressure and temperature. Therefore, mineral composition helps geologists determine the rock type and the processes that formed it.

3. The rock cycle has no beginning and no end.’ Justify this statement with examples.

Answer: The rock cycle is a continuous process where rocks change from one type to another over time. For instance, igneous rocks formed from cooled magma can be broken down into sediments and compressed into sedimentary rocks. These may later be subjected to heat and pressure to become metamorphic rocks. Metamorphic rocks can melt again, forming magma that cools to become new igneous rocks. This cycle has no fixed starting or ending point, as any rock type can transform into another, demonstrating the dynamic and ongoing nature of Earth’s geology.

Project/Activity

1. Rock collection is a great hobby. Collect rock samples from different places and name them.

Answer: Do it yourself. Here are the instructions:

Look for different rocks in your surroundings such as parks, gardens, roadsides, construction sites (with permission), or riversides.
Choose rocks that look different from each other in terms of colour, texture, and hardness.
Use a clean cloth to wipe off any dust or mud from the rocks.
Carry a small notebook or use your phone to note where each rock was collected.
Try to identify the rocks by comparing them with pictures of common types:
- Granite (hard, multi-coloured specks)
- Basalt (dark, fine-grained)
- Sandstone (grainy, usually light brown or reddish)
- Marble (smooth, shiny, often white or pink)
Label each rock with a small sticker or tag (example: Rock A – near river, Rock B – school ground).
Keep the rocks in a box or tray for your collection.

2. Go around your area and survey the rocks. Write down your observations.

Answer: Do it yourself. Here are the instructions:

Take a notebook and pen/pencil with you.
Walk around your area and observe places where rocks are visible (walls, pavements, gardens, empty plots, etc.).
For each place, write:
- Location (e.g., near school gate, in park)
- Type of rock (if known or based on guess – e.g., hard, smooth, layered, soft)
- Colour (e.g., grey, black, white with spots)
- Texture (e.g., rough, grainy, smooth, shiny)
- Any layers or fossils visible (for example, lines in the rock or shell marks)
Take pictures if possible for better recording.
At home, compare your notes and see if you can tell the difference between igneous, sedimentary, and metamorphic rocks using simple charts or online guides.

Extras

Additional MCQs

1. A rock can be defined as an aggregate of which of the following?

A. Minerals
B. Metals
C. Elements
D. Compounds

Answer: A. Minerals

2. Which of the following has no definite chemical composition?

A. Rock
B. Mineral
C. Compound
D. Element

Answer: A. Rock

3. Minerals differ from rocks in that minerals have which characteristic?

A. Definite chemical composition
B. No colour
C. No hardness
D. No structure

Answer: A. Definite chemical composition

4. Which three types of rocks are based on origin?

A. Igneous, sedimentary, metamorphic
B. Quartz, basalt, sandstone
C. Marble, slate, schist
D. Fossil, organic, chemical

Answer: A. Igneous, sedimentary, metamorphic

5. Igneous rocks form by which process?

A. Solidification of magma
B. Deposition of sediments
C. Alteration by heat
D. Compaction of clay

Answer: A. Solidification of magma

6. Which rock type is also called primary rock?

A. Igneous
B. Sedimentary
C. Metamorphic
D. Clastic

Answer: A. Igneous

7. Extrusive igneous rocks form when magma does what?

A. Cools on the surface
B. Cools below the crust
C. Is compacted
D. Is cemented

Answer: A. Cools on the surface

8. Basalt is an example of which igneous rock?

A. Extrusive
B. Intrusive
C. Metamorphic
D. Sedimentary

Answer: A. Extrusive

9. Which igneous rock forms large crystals due to slow cooling?

A. Granite
B. Basalt
C. Obsidian
D. Pumice

Answer: A. Granite

10. Dykes form when magma does what?

A. Fills vertical cracks
B. Flows horizontally
C. Erupts as lava
D. Cements sediments

Answer: A. Fills vertical cracks

11. Batholiths are best described as which of the following?

A. Dome-shaped intrusions at depth
B. Surface lava flows
C. Sedimentary basins
D. Metamorphic bands

Answer: A. Dome-shaped intrusions at depth

12. Laccoliths are characterised by which shape?

A. Dome top and flat bottom
B. Vertical fissures
C. Cylindrical columns
D. Sheet flows

Answer: A. Dome top and flat bottom

13. Sills occur when magma does what?

A. Flows between rock layers
B. Solidifies in vertical cracks
C. Extrudes as lava
D. Forms hexagonal columns

Answer: A. Flows between rock layers

14. Pumice is an example of which rock type?

A. Igneous
B. Sedimentary
C. Metamorphic
D. Clastic

Answer: A. Igneous

15. Sedimentary rocks are formed by which overall process?

A. Lithification of sediments
B. Cooling of magma
C. Heat and pressure
D. Crystallisation

Answer: A. Lithification of sediments

16. Which process involves evaporation in rock formation?

A. Formation of rock salt
B. Compaction of sand
C. Cementation by silica
D. Foliation development

Answer: A. Formation of rock salt

17. Compaction in sedimentary rocks refers to what action?

A. Squeezing by overlying layers
B. Precipitation of minerals
C. Accumulation of organic matter
D. Dissolution by water

Answer: A. Squeezing by overlying layers

18. Cementation bonds sediments using which materials?

A. Natural cements like silica
B. Organic acids
C. Fossil remains
D. Wind deposits

Answer: A. Natural cements like silica

19. Shale and sandstone are examples of which sedimentary rocks?

A. Mechanically formed
B. Chemically formed
C. Organically formed
D. Metamorphic

Answer: A. Mechanically formed

20. Gypsum is classified as which sedimentary rock?

A. Chemical
B. Clastic
C. Organic
D. Metamorphic

Answer: A. Chemical

21. Limestone primarily consists of which compound?

A. Calcium carbonate
B. Silica
C. Iron oxide
D. Sodium chloride

Answer: A. Calcium carbonate

22. Coal in its final stage with high carbon content is called what?

A. Anthracite
B. Lignite
C. Peat
D. Bituminous

Answer: A. Anthracite

23. Loess is a deposit formed by which agent?

A. Wind
B. Glaciers
C. Rivers
D. Marine currents

Answer: A. Wind

24. Marine calcareous rocks are formed on the what?

A. Ocean floor
B. Mountain peaks
C. Desert plains
D. River valleys

Answer: A. Ocean floor

25. Metamorphic rocks originate from which process?

A. Alteration of pre-existing rocks
B. Deposition of sediments
C. Solidification of magma
D. Evaporation processes

Answer: A. Alteration of pre-existing rocks

26. Slate is formed from which original rock?

A. Shale
B. Limestone
C. Sandstone
D. Basalt

Answer: A. Shale

27. Marble originates from metamorphism of what?

A. Limestone
B. Shale
C. Basalt
D. Sandstone

Answer: A. Limestone

28. Foliation in metamorphic rocks is due to what?

A. Banded mineral arrangement
B. Evaporation
C. Compaction
D. Sediment deposition

Answer: A. Banded mineral arrangement

29. Schist is a metamorphic rock known for what feature?

A. Pronounced foliation
B. Vesicular texture
C. Fine layering
D. Chemical precipitation

Answer: A. Pronounced foliation

30. Which metamorphism is due to high temperature alone?

A. Thermal
B. Dynamic
C. Regional
D. Contact

Answer: A. Thermal

31. Regional metamorphism occurs during what event?

A. Mountain building
B. Volcanic eruptions
C. Sediment compaction
D. Evaporation

Answer: A. Mountain building

32. Which rock type is generally impermeable and does not allow water percolation?

A. Metamorphic
B. Sedimentary
C. Igneous
D. Clastic

Answer: A. Metamorphic

33. The rock cycle illustrates transformations among which rocks?

A. Igneous, sedimentary and metamorphic
B. Minerals, metals and ores
C. Elements, compounds and mixtures
D. Rocks, soils and sediments

Answer: A. Igneous, sedimentary and metamorphic

34. Which process recycles disintegrated rocks into magma?

A. Melting
B. Evaporation
C. Cementation
D. Compaction

Answer: A. Melting

35. Gypsum is used to make which material?

A. Plaster of Paris
B. Concrete
C. Steel
D. Glass

Answer: A. Plaster of Paris

36. Quartzite is formed by recrystallisation of which rock?

A. Quartz-rich sandstone
B. Shale
C. Limestone
D. Basalt

Answer: A. Quartz-rich sandstone

37. Granite is classified as which igneous rock based on silica content?

A. Acid
B. Basic
C. Clastic
D. Organic

Answer: A. Acid

38. Basalt is classified as which igneous rock based on chemical composition?

A. Basic
B. Acid
C. Organic
D. Chemical

Answer: A. Basic

39. Hypabyssal rocks form at which depths?

A. Intermediate
B. Surface
C. Deep
D. Oceanic

Answer: A. Intermediate

40. Which mineral group does feldspar belong to?

A. Silicates
B. Carbonates
C. Sulphides
D. Metallic

Answer: A. Silicates

41. Which is the most abundant mineral element in the earth’s crust?

A. Silicon
B. Iron
C. Calcium
D. Nickel

Answer: A. Silicon

42. The earth as a whole contains more of which element compared to the crust?

A. Iron
B. Aluminium
C. Potassium
D. Sodium

Answer: A. Iron

43. Which rock type often contains fossils?

A. Sedimentary
B. Igneous
C. Metamorphic
D. Hypabyssal

Answer: A. Sedimentary

44. Which term describes the bonding of compacted sediments?

A. Cementation
B. Lithification
C. Compaction
D. Foliation

Answer: A. Cementation

45. Which factor does not directly form metamorphic rocks?

A. Wind deposition
B. Heat
C. Pressure
D. Chemically active gases

Answer: A. Wind deposition

46. Sedimentary rocks are generally not which of the following?

A. Crystalline
B. Layered
C. Soft
D. Stratified

Answer: A. Crystalline

47. Which igneous rock is typically associated with volcanic regions?

A. Basalt
B. Slate
C. Quartzite
D. Marble

Answer: A. Basalt

48. Which process removes water from sediments?

A. Evaporation
B. Compaction
C. Cementation
D. Foliation

Answer: A. Evaporation

49. Rock salt forms by which process?

A. Evaporation
B. Compaction
C. Foliation
D. Metamorphism

Answer: A. Evaporation

50. Gabbro is an example of which igneous rock?

A. Intrusive
B. Extrusive
C. Sedimentary
D. Metamorphic

Answer: A. Intrusive

Additional Assertion and Reason

1. Assertion (A): Igneous rocks are hard and compact.
Reason (R): They are formed by solidification of molten magma.