Selina Concise Solutions for ICSE Class 9 Geography Chapter 6 Rocks

Exercises

I. Short Answer Questions

Question 1: State two points of distinction between rocks and minerals.
Answer: Rocks :
1. Rocks contain minerals.
2. Rocks are the aggregates of minerals and other rock material.
Minerals :
1. Minerals do not contain rocks.
2. Mineral are the compounds of pure elements with a definite chemical Composition.
Rocks are like a big bowl of mixed cereal where different grains are combined. Minerals are the individual pure grains that have their own unique recipe and structure.
Teacher's Tip: Think of Rocks as the "Whole Cake" and Minerals as the "Ingredients" like flour and sugar.
Exam Tip: Always mention that minerals have a "definite chemical composition" to get full marks.

Question 2: Name any three elements of the earth’s crust.
Answer: These are silicon, aluminium, iron, magnesium, calcium, potassium, sodium and nickel.
The Earth’s crust is made up of these natural chemicals that join together to make rocks. Silicon and aluminium are the most common ones found in the land we walk on.
Teacher's Tip: Just remember the word "SIAL" for Silicon and Aluminium.
Exam Tip: If the question asks for three, list the first three mentioned in the book to stay accurate.

Question 3: Name three types of rocks.
Answer: Three types of rocks are sedimentary, igneous and metamorphic rocks.
These three families of rocks are sorted by how they were born, either from volcanoes, water layers, or heat and pressure. Every rock you find on Earth belongs to one of these three groups.
Teacher's Tip: Use the "I-S-M" trick: Igneous, Sedimentary, Metamorphic.
Exam Tip: Make sure you can spell "Metamorphic" correctly, as it is a very common spelling error.

Question 4: Why are the igneous rocks also called the primary rocks?
Answer: The igneous rocks were the first to be formed. They form the basis of formation of other types of rocks. Thus, they are called primary rocks.
Igneous rocks are the "parent" rocks because they formed directly from the cooling of the Earth’s original molten state. All other rocks on our planet are made from pieces of these original rocks.
Teacher's Tip: "Primary" means "First" - just like primary school is your first school!
Exam Tip: To score full marks, explain that they provide the raw material for other rock types.

Question 5: Give one difference between Extrusive igneous and Intrusive igneous rocks.
Answer: Extrusive igneous rocks are formed by the cooling of molten magma on the earth’s surface.
Intrusive igneous rocks are formed when the magma solidifies within the earth’s crust forming coarse texture.
Extrusive rocks are "outdoor" rocks that cool fast after a volcano erupts. Intrusive rocks are "indoor" rocks that cool slowly deep underground, which gives them big, bumpy crystals.
Teacher's Tip: "Ex" means Exit (outside) and "In" means Inside.
Exam Tip: Mention "cooling rate" or "texture" to show you understand the difference in how they look.

Question 6: Name any two chief characteristics of Igneous Rocks.
Answer: Igneous rocks are formed by cooling of magma and these are crystalline rocks and full of mineral compounds.
These rocks are very tough and don't have layers or fossils because they were born in fire. They are made of shiny crystals that fit together like a puzzle.
Teacher's Tip: Remember: No Fossils in Fire! (Igneous rocks don't have them).
Exam Tip: Use the word "crystalline" as it is a key technical term for igneous rocks.

Question 7: What is the main characteristics of Basic Igneous Rocks?
Answer: Basic igneous rocks have higher percentage of oxides of denser elements and dark in colour, e.g. Basalt, dolerite etc.
These are the heavy, dark rocks that make up the ocean floor. They don't have much silica (sand-like material) but have lots of heavy metals like iron.
Teacher's Tip: Basic = Black and Basalt (they all start with B!).
Exam Tip: Always give an example like "Basalt" when describing a type of rock.

Question 8: Name two important landforms made by Igneous Rocks.
Answer: Conical mountains and extensive lava plateaus.
Volcanoes usually form a cone shape because the lava piles up around the opening. Sometimes the lava is so thin it spreads out for miles to create a giant flat plateau.
Teacher's Tip: Think of a "V" for Volcano (Conical) and a "P" for Plateau (Flat).
Exam Tip: Use the word "extensive" to describe the large size of lava plateaus.

Question 9: What are Sills ?
Answer: The magma takes place in between the layers of rocks and hardens after cooling, which is called Sill.
A sill is like a "shelf" of rock. It happens when liquid magma squeezes horizontally between layers of older rock and freezes there.
Teacher's Tip: Sills are like a window sill - they are always flat and horizontal.
Exam Tip: Specify that sills are parallel to the existing rock layers.

Question 10: Which rocks are associated with ores of metals ?
Answer: Igneous rocks are associated with ores of metals due to their origin by cooling magma resulting in crystalline rocks rich in mineral content.
Most of our gold, copper, and iron comes from igneous rocks. The extreme heat of the magma melts these metals and concentrates them into veins that we can mine.
Teacher's Tip: Fire (Igneous) creates Fortune (Metals).
Exam Tip: Link the metal content to the "volcanic origin" of the rocks.

Question 11: Which rocks are associated with fossil fuels ?
Answer: Sedimentary rocks are associated with fossil fuels due to fossils trapped in between layers of these rocks.
Coal and oil are made from dead plants and animals that were buried under mud millions of years ago. Only sedimentary rocks have the layers needed to trap and squash these remains into fuel.
Teacher's Tip: S-S-S: Sedimentary, Strata (layers), and Skeletons (fossils).
Exam Tip: Explain that the "stratified" or layered nature is what allows fossils to be preserved.

Question 12: Mention any two chief characteristics of Sedimentary Rocks.
Answer: Sedimentary rocks are formed from material derived from other rocks including plant and animal remains. These rocks thus contain fossils.
Sedimentary rocks are generally not crystalline. They are soft and layered as they are formed by deposition of sediments.
These rocks are the only ones that tell the history of life on Earth through fossils. They are made of tiny bits of sand or mud that settled at the bottom of water and became hard.
Teacher's Tip: Think of Sedimentary rocks as the "Storybooks" of Earth because of their layers and fossils.
Exam Tip: Use the word "non-crystalline" to contrast them with igneous rocks.

Question 13: Give two examples of Sedimentary Rocks.
Answer: 1. Sandstone
2. Limestone
Sandstone is made of tiny grains of sand glued together, and Limestone is often made from the crushed shells of sea creatures. Both are common rocks used for building.
Teacher's Tip: Sandstone feels "sandy" to the touch!
Exam Tip: These are the two most common examples; memorize them first.

Question 14: Name the rocks which are most widespread on the earth.
Answer: Sedimentary rocks are most widespread on the earth.
While the deep inside of the Earth is mostly igneous, the "skin" or top surface that we see is mostly covered by sedimentary rocks. They cover about three-quarters of the land surface.
Teacher's Tip: Most of what you see on the surface is Sedimentary!
Exam Tip: Differentiate between the "crust's volume" (mostly igneous) and "crust's surface" (mostly sedimentary).

Question 15: Name the three stages of lithification of Sedimentary rocks.
Answer: Lithification is the process of turning loose rock material into hard rock through evaporation, compaction and cementation.
First, the water dries out of the mud. Then, the weight of more mud on top squashes the bottom layers together until they finally get "glued" into solid rock.
Teacher's Tip: Think of "ECC": Evaporation, Compaction, Cementation.
Exam Tip: Define "lithification" as the process of "turning loose material into solid rock."

Question 16: Name the types Sedimentary rocks based on agents of formation.
Answer: There are five main types of rocks on the basis of agents of formation:
1. Riverine Rocks These are formed by the sediments deposited by running water or river.
2. Lacustrine Rocks These are formed by the deposition of silt etc on the bed of lakes.
3. Glacial Rocks These are formed by the debris carried on and deposited by glaciers.
4. Aeolean Rocks These are formed by the deposition sand accumulation by the wind.
5. Marine Rocks These are formed by the deposition of sediments at the ocean floor. These types are Calcarious and Carbonaceous sedimentary Rocks.
These names tell us who "delivered" the dirt to that spot. Whether it was a river, the wind, or a slow-moving glacier, it created a different kind of sedimentary rock.
Teacher's Tip: "Aeolean" comes from the name of the Greek god of wind, Aeolus!
Exam Tip: Be able to match the "agent" (like wind) to the specific name (like Aeolean).

Question 17: Which agents are responsible for deposition of sediments?
Answer: There are three main agents of deposition i.e., water, wind and ice, which mainly act as agents of change on the surface of earth for deposition of sediments.
Water is the strongest agent, carrying mud to the sea. Wind carries sand in deserts, and heavy ice (glaciers) pushes giant boulders across the land.
Teacher's Tip: Just remember "W-W-I": Water, Wind, and Ice.
Exam Tip: Use the word "agents" to describe these natural forces.

Question 18: What are known as metamorphic rocks ? Give two examples.
Answer: Metamorphic rocks are formed by complete change of texture of rocks through volcanism and diastrophism, e.g., limestone is converted to marble and shale is transformed to slate.
These are "makeover" rocks. They don't melt, but the intense heat and pressure deep underground bake them into a much harder and different form.
Teacher's Tip: Think of "Metamorphosis" - just like a caterpillar turns into a butterfly!
Exam Tip: Always mention both "heat" and "pressure" as the causes of metamorphism.

Question 19: What is Mechanical Metamorphism ?
Answer: This is a mechanical Transformation in which texture of rocks is changed by crushing and rubbing processes associated with heat and compression created by mechanical action.
This happens during big events like earthquakes or mountains being pushed up. The rocks literally grind against each other so hard that they change their internal structure.
Teacher's Tip: Think of "Mechanical" as "Moving parts" or "Friction."
Exam Tip: Use the words "crushing" and "rubbing" to describe this process.

Question 20: What is meant by Rock Cycle ?
Answer: The earth is said to be 4700 million years old and the rocks came into existence 3400 years ago. Since then these rocks have undergone various changes by which multiple transformation took place within the rocks. This continuous process of transformation of old rocks into new rocks is known as rock cycle for figure See Page no. of this book.
The Earth never stops recycling its rocks. An old rock can be melted into magma, turn into an igneous rock, get washed away into a sedimentary layer, and then get baked into a metamorphic rock.
Teacher's Tip: It is a circle that never ends! Every rock type can become any other rock type.
Exam Tip: Mention that the rock cycle involves "continuous transformation."

Question 21: What processes are involved in the formation of Igneous Rocks ?
Answer: Igneous rocks are associated with volcanic activity, cooling of magma and mechanical weathering etc.
The biggest steps are the melting of rock deep underground and then the cooling of that liquid rock. Once it turns solid again, it is an igneous rock.
Teacher's Tip: Think of it like water turning into ice in a freezer - but with fire!
Exam Tip: Focus on "cooling and solidification" as the two primary processes.

II. Explain these terms associated with rocks.

Question 1: Extrusive Igneous Rocks.
Answer: These rocks are formed by consolidation of erupted magma on the surface of earth.
When liquid lava shoots out of a volcano, it cools down very quickly in the open air. This creates rocks like basalt that have very small crystals because they didn't have much time to grow.
Teacher's Tip: "Extrusive" = "Exited" the volcano.
Exam Tip: State that these rocks are also called "Volcanic rocks."

Question 2: Laccoliths and Batholiths.
Answer: Laccoliths is formed by the intrusion of magma in the erupting channel just below the crust. Batholiths are deep seated dome shaped formation of magma intrusion, generally forming the base of mountain ranges, e.g., Ranchi Batholiths.
These are giant "underground bubbles" of frozen magma. A batholith is so big that it can form the core of a whole mountain range!
Teacher's Tip: A Batholith is "Big" and at the "Bottom."
Exam Tip: Describe batholiths as "dome-shaped" to be precise.

Question 3: Fossil fuels.
Answer: These are the fuels accumulated between two impermeable layers of the sedimentary rocks, e.g. peat, coal and petroleum etc.
These are ancient sun-energy trapped in rocks. They only form when organic matter is squashed between layers that won't let gas or liquid escape.
Teacher's Tip: Coal and Oil are "Fossils" you can burn!
Exam Tip: Mention "impermeable layers" to show why the fuels stayed trapped there.

Question 4: Lithification of Rocks.
Answer: It is the process of turning the loose material into hard rock, which helps in the formation of the sedimentary rocks found in different layers one upon another.
Loose sand and dirt aren't rocks yet. Lithification is the "hardening" magic that turns that soft material into a solid stone block.
Teacher's Tip: Think of it like wet sand drying into a hard sandcastle!
Exam Tip: Make sure you can link this specifically to the formation of "sedimentary" rocks.

Question 5: Metamorphism.
Answer: It is the process of transformation of sedimentary and igneous rocks into metamorphic rocks through extreme temperature and compression by volcanism and diatrophism by physical and Chemical changes.
This is like "extreme baking" for rocks. It changes the rock's minerals and how they look without melting them into liquid magma.
Teacher's Tip: No Melting! If it melts, it becomes Igneous. If it just changes, it's Metamorphism.
Exam Tip: Mention that both "physical" and "chemical" changes happen during this process.

III. Distinguish between each of the following

P Q: Lava and Magma.
Answer: Lava : Lava is the black molten material erupted in a volcano.
Magma : Magma is the compound of lava, stones, ash, debris etc. erupting out in a volcano.
Magma is the hot liquid soup while it is still hiding underground. Once it bursts out and hits the surface, we change its name to lava.
Teacher's Tip: Magma is "Medium" (in the middle of the earth), Lava has "Left" (the volcano).
Exam Tip: The main difference is the "location" (underground vs. surface).

Question 1: Plutonic and Volcanic rocks.
Answer: Plutonic rocks :
1. These are intrusive igneous rocks.
2. These cool down very slowly due to heat in the interior
Volcanic rocks :
1. These are extrusive igneous rocks.
2. These cool down abruptly due to less temperature on the surface region.
Plutonic rocks are the "slow cookers" of the Earth, taking thousands of years to cool. Volcanic rocks are "instant frozen" as soon as they touch the air or water outside.
Teacher's Tip: Plutonic is from "Pluto," the god of the underworld - so they are deep!
Exam Tip: Link "slow cooling" to "large crystals" for Plutonic rocks.

Question 2: Thermal and Dynamic Metamorphism.
Answer: Thermal Metamorphism :
1. It takes place due to extreme temperature which transforms the shape and texture of rocks.
2. The heat may be due to hot magma or friction of rocks.
Dynamic Metamorphism :
1. It takes place due to excessive compression created by tectonic forces within the earth.
2. It takes place through physical or chemical changes by deep pressure.
Thermal metamorphism is like cooking a rock in a hot oven. Dynamic metamorphism is like squashing a rock in a giant, powerful vise.
Teacher's Tip: Thermal = Temperature; Dynamic = Pressure.
Exam Tip: Be sure to mention "hot magma" as a source for thermal metamorphism.

Question 3: Sills and Dykes.
Answer: Sills : The collection of magma between layers of rocks is called sill.
Dykes : The fillings of magma in the cracks or fissures of rocks are called dykes.
Sills are horizontal layers, like a rug on the floor. Dykes are vertical walls, like a door in a room, that cut across other layers.
Teacher's Tip: Sills are "Sleepy" (horizontal); Dykes are "Descending" (vertical).
Exam Tip: Use the words "parallel" for sills and "vertical/transverse" for dykes.

Question 4: Calcarious and Carbonacious rocks.
Answer: Calcarious rocks : The sedimentary rocks formed by the deposition of shells, skeletons of sea organism as corals, clams and oysters etc. are called calcarious rocks due to excess of calcium.
Carbonacious rocks : The sedimentary rocks formed by the deposition of large scale vegetation and animals etc. are called carbonacious rocks due to the excess of carbon.
Calcarious rocks come from the hard white parts of sea life, like chalk. Carbonacious rocks come from rotting plants and trees that turned black, like coal.
Teacher's Tip: Calcarious = Calcium (White); Carbonacious = Carbon (Black).
Exam Tip: Give an example for each: Limestone for Calcarious and Coal for Carbonacious.

Question 5: Acid Igneous Rocks and Basic Igneous Rocks.
Answer: Acid Igneous rocks : These are lighter rocks with silica content 65 to 85 percent with density less than $2\text{ g/cm}^3$, e.g. Granite.
Basic igneous rocks : These are denser rocks with silica content 40 to 60 percent with average density between $2.8\text{ g/cm}^3$ and $3.0\text{ g/cm}^3$ e.g. Basalt.
Acid rocks have lots of "glassy" silica and are light in weight and color. Basic rocks have more heavy metals and are dark and dense.
Teacher's Tip: Acid = Light color (Granite); Basic = Dark color (Basalt).
Exam Tip: Memorize the silica percentages: 65-85% for Acid and 40-60% for Basic.

IV. State the types of rocks for the formation of which the following processes are involved.

Question 1: Solidification of magma on the surface of the earth.
Answer: Extrusive igneous rocks
These rocks harden outside the Earth's crust. They usually have very small or no crystals because they cool too fast.
Teacher's Tip: Surface = Extrusive.
Exam Tip: Basalt is the most common answer for an example of this.

Question 2: Formation of large crystals, coarse texture and slow cooling and compaction.
Answer: Intrusive igneous rocks.
Because these stay underground where it's warm, they cool down very slowly. This gives the minerals lots of time to grow into big, beautiful crystals.
Teacher's Tip: Large crystals mean it cooled "In" the earth.
Exam Tip: Mention "Granite" as a typical intrusive rock.

Question 3: Accumulation takes place over long periods of time in seas, lakes and streams.
Answer: Sedimentary rocks.
These are made of layers of "leftovers" like mud and sand. Over time, these piles get so heavy that they squeeze into solid rock.
Teacher's Tip: Water + Time = Sedimentary.
Exam Tip: These rocks are always found in "layers" or "strata."

Question 4: Decomposition of organic matter at different stages and over different periods of time.
Answer: Carbonaceous Sedimentary rocks.
This is how we get coal. It happens when whole forests are buried and compressed under the Earth's surface for millions of years.
Teacher's Tip: Organic matter means anything that was once alive.
Exam Tip: Coal, peat, and lignite are the main examples here.

V. Long Answer Questions

Question 1: Distinguish between rocks and minerals.
Answer: The rocks contain minerals in the form of ores, but minerals do not contain rocks. Sedimentary rocks contain fossil fuels like coal and petroleum etc, igneous rocks are rich in minerals like copper, gold, iron etc, metamorphic rocks contain valuable building stones like marble and garnet, feldspar etc. Rocks have no definite chemical composition, while minerals have particular chemical composition.
Minerals are the "pure" chemical compounds found in nature. Rocks are the "mixed" lumps that we find on the ground which are made of many different minerals stuck together.
Teacher's Tip: Minerals are the "Atoms" of the geological world, and Rocks are the "Molecules."
Exam Tip: Highlight that minerals have a "particular chemical composition" while rocks do not.

Question 2: Describe how are igneous rocks formed ? State their chief characteristics.
Answer: Igneous rocks are formed by melting and cooling of magma originated from volcanic eruptions. These may be formed by diastrophism and volcanism. These rocks are strong, crystalline and dark in colour. These may be extrusive and intrusive on the surface and beneath the crust respectively.
Igneous rocks are born when hot liquid rock (magma) turns into a solid. They are very tough, often have shiny crystals, and are the "ancestors" of all other rocks on Earth.
Teacher's Tip: Igneous comes from the word "Ignis," which means "Fire."
Exam Tip: Note that these rocks are "hard and compact" and do not contain fossils.

Question 3: How are igneous rocks classified on the basis of their chemical composition?
Answer: On the basis of chemical composition igneous rocks may be classified into two groups i.e. Acid igneous rocks and Basic igneous rocks. Acid rocks have silica content 65-85 percent e.g. granite which is made up of large crystals of quartz, feldspar and mica. Basic rocks contain high percentage oxides of denser material, silica content is between 40-60 percent with a density of $2.8\text{ g/cm}^3$ and $3.0\text{ g/cm}^3$. Acid rocks are lighter than Basic rocks. Basic rocks.
We sort them by how much silica they have. High-silica rocks are light and "acidic," while low-silica rocks are heavy, dark, and "basic."
Teacher's Tip: Acid = Light Weight; Basic = Heavy Weight.
Exam Tip: Use "Granite" as the example for Acid and "Basalt" for Basic rocks.

Question 4: Classify the igneous rocks on the basis of their place of origin.
Answer: On the basis of origin igneous rocks are divided into two groups i.e. Extrusive and Instrusive igneous rocks. Extrusive igneous rocks are found on the surface of the earth by cooling down of erupted magma. Intrusive igneous rocks are formed beneath the earth’s crust after solidification of magma.
It's all about where the "freezing" happened. If it happened in the cold air outside, it's extrusive; if it happened in the warm ground inside, it's intrusive.
Teacher's Tip: Ex-Surface, In-Side.
Exam Tip: Explain that "Intrusive" rocks are also known as "Plutonic" rocks.

Question 5: How are sedimentary rocks formed ?
Answer: Continuous deposition of sediments of silt, soil, debris etc. by water, wind and ice along lower landforms and solidification into different layers result in the formation of light sedimentary rocks.
Rivers and wind carry "trash" like sand and mud and drop it in big piles. Over millions of years, the weight of the top layers squashes the bottom layers into solid stone.
Teacher's Tip: Think of it as "Layer-making."
Exam Tip: Use the word "solidification" to describe how the loose layers become rock.

Question 6: Explain the formation of sedimentary rocks on the basis of agents of formation.
Answer: There are five main types of rocks on the basis of agents of formation:
1. Riverine Rocks These are formed by the sediments deposited by running water or river.
2. Lacustrine Rocks These are formed by the deposition of silt etc on the bed of lakes.
3. Glacial Rocks These are formed by the debris carried oh and deposited by glaciers.
4. Aeolean Rocks These are formed by the deposition sand accumulation by the wind.
5. Marine Rocks These are formed by the deposition of sediments at the ocean floor. These types are Calcarious and Carbonaceous sedimentary Rocks.
This classification looks at "who" moved the rock pieces. Whether it was a river, a lake, a glacier, or the wind, it created a specific type of sedimentary rock.
Teacher's Tip: "Marine" always means the ocean!
Exam Tip: Be ready to define each of the five types with their specific agent (e.g., Wind for Aeolean).

Question 7: How are sedimentary rocks classified on the basis of their formation ?
Answer: There are three types of this type of rocks :
1. Mechanically formed rocks : Denudation of rocks by agents of change results in layers of sedimentary rocks by mechanism.
2. Chemically formed rocks : These are formed by evaporation of calcarious water and accumulated along lake and lagoon beds, e.g. gypsum and rock salt.
3. Organically formed rocks : These are formed by deposition of dead plants and animals e.g. limestone rock (or Calcareous rock) lignite, bituminous and anthracite coal are carbonaceous rocks formed by compression of vegetation under the layers of sedimentary rocks. In the same way petroleum in between the sedimentary rocks is the result of zurasic age dinosaurs e.g. shale rock, containing oil.
Rocks can be made by "squashing" (mechanical), "drying up" (chemical), or "burying life" (organic). Each method creates a unique kind of rock like salt or coal.
Teacher's Tip: Mechanical = Motion; Chemical = Chemistry; Organic = Once-alive.
Exam Tip: Mention "Gypsum" for chemical and "Coal" for organic to show specific knowledge.

Question 8: What is metamorphism ? What are its causes ?
Answer: Metamorphism is a process of transformation of sedimentary and igneous rocks into the metamorphic rocks through physical and chemical reactions. Main causes are great temperature and pressure beneath the earth’s crust, which changes the original texture and form of the rocks into dense, crystalline and fine grained rocks.
Metamorphism is like a "Total Transformation" for rocks. When they get squashed and baked deep in the Earth, they change their look and feel without actually melting.
Teacher's Tip: It is a complete "Texture" change!
Exam Tip: Temperature and Pressure are the two required "ingredients" for this to happen.

Question 9: What are the chief characteristics of metamorphic rocks?
Answer: Metamorphic rocks are composed of fine particles and dense, smooth material. These are very precious rocks, particularly for building stones like marble, garnet, slate quartzite etc.
Because they were squashed so hard, these rocks are very strong and smooth. They often have shiny bands and are used for beautiful things like statues and fancy floors.
Teacher's Tip: Smooth and Shiny! (Think of Marble).
Exam Tip: List "Marble" or "Quartzite" as examples of their value.

Question 10: What is Rock Cycle. How does it keep the earth young?
Answer: The earth is said to be 4700 million years old and the rocks came into existence 3400 years ago. Since then these rocks have undergone various changes by which multiple transformation took place within the rocks. This continuous process of transformation of old rocks into new rocks is known as rock cycle.
To keep the earth young, rock melts again resulting in formation of igneous rock. This disintegrated material again form sedimentary rock, it takes hundreds are thousands years.
The Rock Cycle is Earth's giant recycling system. By constantly melting old rocks and making new ones, the Earth keeps its surface fresh and moving instead of just being a dead ball of old dust.
Teacher's Tip: It's like a never-ending circle!
Exam Tip: Explain that "melting" and "disintegration" are key parts of how the cycle keeps the Earth "young."

Question 11: Give a detailed account of lithiflcation of sedimentary rocks.
Answer: Lithification means solidification. The loose material carried on by water, wind and ice is deposited slowly in different layers one upon another. Gradually the deposited sediments become solid and hard due to pressure and temperature. Evaporation results in the loss of water within the sediments and these are compacted and cemented. Compaction takes place by increasing weight and pressure of over lying sediments e.g. sand is converted to sandstone. Cementation takes place by bonding of compacted sediments by natural elements like calcium compounds, silica and iron with a property to bind the loose materials to solid state.
Lithification is the three-step "Rock-Maker" process. First, the water dries out, then the heavy weight on top squashes the dirt, and finally natural minerals act like glue to lock everything together into stone.
Teacher's Tip: "Lith" means "Rock" - so Lithification is "Making a rock."
Exam Tip: Use the words "Compaction" and "Cementation" as they are the most important terms in this process.

Practice Questions (Solved)

Question 1: (a) What is meant by a rock ? Or What is meant by a ‘rock’ ? Name the main types of rocks.
(b) Differentiate between Rock and Mineral
(c) How are sedimentary and igneous rocks formed ?
(d) In what type of rocks do you find fossils and why ?
(e) How are rocks important to us ?
Answer: (a) Rock : A rock can be defined as “an aggregate of minerals that forms a more or less definite unit of the earth’s crust”. A rock does not possess a definite composition like that of a chemical compounds, but is usually a mixture of various minerals. The bulk of rocks is made up of silica or quartz and feldspar. Feldspar are composed of silica, aluminium, potassium and sodium or calcium. Some rocks are composed of grains cemented together, while several other are crystalline, compact or even glass- like. All material (whether hard like stone or sand) of which the crust of the earth is composed are called rocks e.g, stone, clay, lava, sand, chalk, salt, coal marble etc.. On the basis of their mode of formation, rocks are divided into three types :
• Igneous rocks
• Sedimentary rocks
• Metamorphic rocks.
(b) Rock :
1. A rock is a natural solid organic or inorganic material forming the crust of the earth.
2. A rock is an aggregate of minerals.
3. The physical properties of rocks vary.
Mineral :
1. The mineral is an organic element or compound which occurs naturally.
2. A mineral has an atomic structure.
3. It has fixed definite physical properties.
(c) Formation of Sedimentary rocks : Sedimentary rocks are formed by the process of consolidation of sediments deposited commonly in water bodies like seas or lakes. The sediments are derived by the rivers, glaciers, winds and waves. The sediments consist of loose particles of gravel, sand, silt and clay in various proportions. These loose particles get consolidated or compacted into hard rocks by the presence of cementing substances like lime or the pressure of overlying deposits.
Formation of igneous rocks : The rocks which are formed by the process of solidification of molten rock material (magma), are called igneous rocks. The processes involved in the formation of igneous rocks are cooling and solidification. Two types of igneous rocks are
• Intrusive igneous rocks
• Extrusive igneous rocks.
(d) Fossils are found in sedimentary rocks. Organic remains of plants and animals or their skeletal impressions are called fossils. Fossils help us in fixing the relative ages of rocks.
(e) Rocks are of great economic significance Some of the main benefits of rocks are as follows :
• After disintergration, they turn into valuable soils.
• They are the store-houses of a large number of minerals.
• They are the source of precious metals like gold, silver, platinum etc.
• They are source of fuel-minerals.
• They provide different types of stones.
This giant answer summarizes everything! Rocks are mixtures of minerals that make up our Earth, and they are formed by fire, layers, or change. They are extremely important because they give us our soil to grow food and all the metals and fuels we use in our daily lives.
Teacher's Tip: This question is a "Mega-Summary" of the whole chapter!
Exam Tip: Be able to define "Fossils" as "organic remains" to get full marks in part (d).

Question 2: (a) Name different types of sedimentary rocks.
(b) What physical agents are involved in the sedimentary rocks ?
(c) How are chemically-formed sedimentary rocks produced?
(d) How are chemically-formed sedimentary rocks formed? Give examples.
(e) Sedimentary rocks are also called stratified rocks. Why? OR Why sedimentary rocks are called stratified rocks ?
Answer: (a) There are three types of sedimentary rocks on the basis of the nature of sediments, their origin, composition and mode of formation. These are mechanically-formed sedimentary rocks, organically formed sedimentary rocks and chemically- formed sedimentary rocks.
(b) Rain water, wind, ice or the running water are the agents involved in the formation of sedimentary rocks. These agents break and carry on loose material and deposit it in various low lying areas to convert into the solid sedimentary rocks.
(c) Chemically-formed sedimentary rocks are produced through evaporation of water from solutions containing minerals. In this ways a rock like ‘gypsum’ is produced. Other examples are nitrates and potash etc.
(d) Chemically formed sedimentary rocks are formed through chemical action of water. Some mineral like limestones and salts are dissolved into the water and after the evaporation of water form a particular type of rock which is formed by the chemical sedimentation of limestones into gypsum and salt into various types of nitrates.
(e) During the formation of sedimentary rocks, the sediments are deposited in waterbodies and get sorted out according to their size. The sediments accumulate in different layers or strata arranged one above the other. Each layer or stratum has particles of given size. In sedimentary rocks each layer or stratum has particles of a given size. Therefore, sedimentary rocks are also called stratified rocks.
Sedimentary rocks are the "layer rocks" created by nature's delivery trucks like wind and rain. They are called stratified because they always form in neat, horizontal layers like a stack of pancakes.
Teacher's Tip: Stratified = Stacked layers.
Exam Tip: If asked why they are "stratified," always mention that they are deposited in "layers or strata."

Question 3: (a) What is meant by the term ‘metamorphism’ ?
(b) Distinguish between Thermal metamorphism and Dynamic metamorphism.
(c) Distinguish between Regional and Contact metamorphism. (d) What are metamorphic rocks ?
(e) Give some examples of metamorphic rocks formed from sedimentary and igneous rocks.
Answer: (a) The term metamorphism means change of form. It may be physical or chemical or both.
(b) Thermal metamorphism : When the transformation of the original rock takes place principally because of the influence of high temperature, the rock is said to be caused through Thermal metamorphism. For example, graphite (from coal) and slate (from clay). The heat may result from the intrusion of hot magma or from the friction of moving rock layers. It may also occur due to chemical changes. Dynamic metamorphism : When the transformation of the original rock takes place mainly because of the influence of pressure at a great depth within the earth’s crust, it is known as Dynamic Metamorphism.
(c) Regional metamorphism When metamorphism of bed rocks takes place over a very large area, it is called Regional metamorphism. It is usually caused by the movement of the earth’s crust. Contact metamorphism when it takes place over a small area, it is called Local Metamorphism or Contact Metamorphism. It commonly occurs when hot magma comes in contact with other rocks.
(d) Metamorphic rocks are those rocks which were formerly igneous or sedimentary rocks, but owing to extreme heat and pressure in the interior of the earth it has been changed or altered to such an extent that they are quite different from what they once were slate, which is in reality clay, and marble’ which is in reality lime stone. Other examples of metamorphic rocks are quartzite from sand stone, graphite from coal, gneiss from granite and Mica from Schist.
(e) (a) Sedimentary Rocks : 1. Limestone 2. Clay and Shale 3. Sandstone 4. Coal Metamorphic Rocks : 1. Marble 2. Slate 3. Quartzite 4. Graphite (b) Igneous Rocks : 1. Granite 2. Basalt Mctamorphic Rocks : 1. Gneiss 2. Schist
This describes how rocks "transform" into stronger versions of themselves. Limestone turns into beautiful Marble, and common Granite turns into Gneiss through massive heat and squeezing.
Teacher's Tip: Regional is for large areas, and Contact is for small spots near hot magma!
Exam Tip: Be ready to name the "before" rock and the "after" rock (e.g., Coal becomes Graphite).

Question 4: Classify the following rocks into sedimentary, igneous and metamorphic.
Answer: (a) Shale - Sedimentary rock
(b) Gneiss - Metamorphic rock
(c) Quartzite - Metamorphic rock
(d) Slate - Metamorphic rock
(e) Marble - Metamorphic rock
(f) Coal - Sedimentary rock
(g) Clay - Sedimentary rock
(h) Schist - Metamorphic rock
(i) Granite - Igneous rock
(j) Graphite - Metamorphic rock
(k) Dolomite - Sedimentary rock
(l) Peat - Sedimentary rock
(m) Basalt - Igneous rock
(n) Rock salt - Sedimentary rock
(o) Lime-stone - Sedimentary rock
(p) Gypsum - Sedimentary rock
(q) Loess - Sedimentary rock
This is a helpful list to memorize for matching questions. It shows that many of the stones we use every day, like salt and coal, are actually types of sedimentary rocks.
Teacher's Tip: Most metamorphic rocks end in "ite" or "ate" (but not all!).
Exam Tip: Granite and Basalt are the most important Igneous rocks to remember for exams.

Question 5: Give one word for the following
(a) The outer layer of the earth.
(b) The lower part of ocean floor, comprising mainly of silica.
(c) Rocks formed by the cooling and solidification of molten rock from beneath the earth crust.
(d) Stratified rock formed organically but from vegetative matter-swamps and forests.
(e) The upper part of lithosphere, which is rich in silica and aluminium.
(f) The core of the earth occupied by rock in iron and nickel.
(g) Igneous rocks, which contain a high percentage of silica.
(h) Igneous rocks, which contain a low percentage of silica.
(i) A sedimentary rock, which is composed of microscopically fine, soft and smooth particles.
(j) The best example of chemically-formed sedimentary rock, which has been formed by the evaporation of water from solution containing minerals.
Answer: (a) Crust
(b) SIMA
(c) Igneous rocks
(d) Carbonaceous rocks
(e) SIAL
(f) Nife
(g) Acidic igneous rocks
(h) Basic igneous rocks
(i) Clay
(j) Gypsum
These are the scientific "IDs" for Earth's layers and rock families. Knowing these words is like knowing the vocabulary of a geologist!
Teacher's Tip: SIAL (Silicon + Aluminium) and SIMA (Silicon + Magnesium) are easy to remember if you split the names!
Exam Tip: For (f), Nife stands for Nickel ($Ni$) and Iron ($Fe$).

Q. 6: Fill in the blanks
Answer: 1. The interior layer is the core, which is made up mainly of iron and nickel, and is called Nife.
2. Organically formed sedimentary rocks are formed by the deposition of shells and skeletons of organism.
3. Breccia rock is formed, when the angular and coarse grains of some durable minerals are cemented together.
4. Aeolian is the best example of the wind deposited stratified rock.
5. Basic igneous rock contain a low percentage of silica and a high percentage of basic oxides.
6. Extrusive rocks are also known as volcanic rocks.
7. Basaltic lava rocks cover wide area in Peninsular India and Columbia, the Snake Plateau of the U.S.A.
These sentences summarize the most important facts about how rocks are made and where they are found. India has a famous area called the Deccan Trap made entirely of volcanic basaltic lava!
Teacher's Tip: Breccia has "Broken" (angular) pieces - they both start with B.
Exam Tip: Be sure to include the "Nife" name when talking about the Earth's core.

Question 7: Give one example of an area of :
1. Igneous rocks
2. Metamorphic rocks,
3. Sedimentary rocks in India
Answer: 1. Deccan Plateau
2. Narmada Basin
3. Himalayan Region
India's geography is like a giant rock collection. The South is volcanic, the center is metamorphic, and the massive mountains in the North are made of ocean sediments!
Teacher's Tip: The Himalayas used to be under the sea - that's why they are sedimentary!
Exam Tip: Memorize these three specific regions as they are common on map-pointing questions.

Question 8: What is the basis for the classification of rocks ?
Answer: The basis for the classification of rocks are their mineral composition, colour and texture.
Scientists don't just guess; they look at what's inside the rock, what color it is, and whether it feels smooth or rough to decide its type.
Teacher's Tip: Think of "M-C-T": Minerals, Color, and Texture.
Exam Tip: Always list "mineral composition" as the most important basis.

Question 9: Why are Sedimentary rocks called the Secondary rocks?
Answer: Sedimentary rocks are called Secondary rocks or derived - rocks because they are derived by the denudation of other rocks.
Because Igneous rocks came first (Primary), and Sedimentary rocks are made from the "leftovers" of broken-down Igneous rocks, they get the name "Secondary."
Teacher's Tip: Think of it like a second-hand toy that was made from old parts!
Exam Tip: Use the word "denudation" to show you understand that weathering and erosion are involved.

Question 10: How are sedimentary rocks classified ?
Answer: Sedimentary rocks are classified into the following types according to the nature of sediments, their origin, composition and the mode of formation.
1. Inorganic rocks or Mechanically-formed Sedimentary Rocks :- These type of rocks are formed by the deposition of land derived material. When the river began to flow, they eroded the rocks and washed away to the sea. Clay, shale, sandstone were formed in this way. These rocks are called inorganic rocks.
2. Organically formed Sedimentary Rocks :- These rocks are formed by the deposition of plants and sea organisms. Millions of years ago, there grew huge forest in marshy places. In course of ages they were buried underground and the internal heat changed them into coal. Moreover, there are millions and millions of sea-organisms whose skeleton are made of Calcium carbonate derived from sea water. After their death skeleton sink to the bottom of the seas and are formed into lime true and chalk and coal.
3. Chemically-formed Sedimentary Rocks :- There rocks are formed by the evaporation of water from solution containing mineral. Various kinds of salts precipitate from waters of shallow desert lakes, where evaporation of the water is rapid. Gypsum is the best example of this kind of rocks. Several nitrates and potash are also chemically formed sedimentary rocks.
This is a long explanation of the "Three Big Families" of sedimentary rocks. They are sorted by whether they were made from physical bits of rock, dead living things, or minerals left behind by drying water.
Teacher's Tip: Mechanical = Pieces; Organic = Life; Chemical = Salt.
Exam Tip: Be sure to mention that "Coal" is an organically formed rock.

Question 11: State the properties of metamorphic rocks.
Answer: Properties of metamorphic rocks :
1. These rocks are harder and more resistant than the original rocks.
2. These rocks have their minerals arranged in a series of bands.
Because they have been "baked and squashed," these rocks are extra tough and don't break easily. You can often see beautiful stripes or "bands" of different minerals inside them.
Teacher's Tip: Bands mean Metamorphic!
Exam Tip: "Resistance" means they don't erode or wear away as fast as other rocks.

Question 12: Give one term for the following statements :
1. Formed when mud layers compacted under great pressure composing 80% of this rock.
2. It has a definite chemical composition with its own chemical and physical properties.
3. Igneous rocks of deep seated origin.
4. Sheet like body of igneous rock.
5. Rounded or sub-rounded fragments, usually water-born cobbles, pebble and gravel, cemented together by a matrix of calcium carbonate, silica, etc.
6. Formed by evaporation in saline lakes.
7. Fine grained metamorphic rock, generally produced by the low grade metamorphism of shale.
8. Type of metamorphism in which changes are caused due to high pressure.
Answer: 1. Shale
2. Mineral
3. Plutonic rocks
4. Sill
5. Conglomerate
6. Rock salt
7. Slate
8. Dynamic metamorphism.
These are the specific dictionary definitions for different geological terms. Conglomerate is a cool rock that looks like a concrete mix with pebbles inside!
Teacher's Tip: Shale is the most common sedimentary rock on Earth!
Exam Tip: Memorize these as "Definitions" for one-mark questions.

Question 13: Why are the Igneous Rocks called Primary Rocks ?
Answer: It is believed that the earth was in a molten state in the beginning Igneous rocks were the first rocks to be formed due to cooling and solidification of molten matter. Hence these are called Primary Rocks.
Think of Igneous rocks as the "Founding Fathers" of all other rocks. Without them, there would be no ingredients to make sedimentary or metamorphic rocks.
Teacher's Tip: Primary = First.
Exam Tip: Mention the "molten state" of early Earth to explain why they formed first.

Question 14: Why fossils are preserved in Sedimentary and not in Igneous rocks ?
Answer: Fossils are remains of vegetation and animals buried under the sediments. The sedimentary rocks are stratified rocks and are found in layers. These fossils are preserved in between these layers. But in Igneous rocks, the fossils are destroyed due to high temperature of lava.
Imagine a leaf falling in cool mud (sedimentary) vs. falling in liquid fire (igneous). The mud will wrap around it and save it, but the fire will turn it into smoke instantly!
Teacher's Tip: Fire destroys Fossils!
Exam Tip: Use the word "stratified" to describe the layers where fossils are kept safe.

Question 15: How is Plutonic rock formed ? Give an example of an Plutonic rock.
Answer: Plutonic rocks are the igneous rocks which are formed as some depth in the earth’s crust, when a molten material gets solidified under pressure. Granite is very good example of a Plutonic rock.
These rocks are the "underground dwellers" that cool down very slowly while trapped inside the Earth. Granite, which we use for kitchen counters, is a perfect example.
Teacher's Tip: Slow cooling = Big Crystals.
Exam Tip: Always use "Granite" as your example for Plutonic rocks.

Question 16: Give reasons for the following :
1. Extrusive rocks generally have small crystals.
2. Silicates are the most common rock forming minerals.
3. Rocks are of great economic significance.
4. Man’s habitat is the biosphere and not the lithosphere in the true sense.
Answer: 1. Extrusive rocks generally have small crystals because in the formation of these rocks, the solidification of magma takes place at a slower rate. (Note: Textbook error, it should be "faster rate").
2. Silicates are the most common rock forming minerals because they are most common minerals in the Earth’s crust.
3. Rocks are of great economic significance Some of the main benefits of rocks are as follows :
• After disintergration, they turn into valuable soils.
• They are the store-houses of a large number of minerals.
• They are the source of precious metals like gold, silver, platinum etc.
• They are source of fuel-minerals.
• They provide different types of stones.
4. The composite zone inhabited by most living creatures is called biosphere. It includes a part of the atmosphere, the hydrosphere and a part of the lithosphere. All three layers are essential for life to exist. As lithosphere is only a small part of the biosphere, therefore, man’s habitat is the biosphere and not the lithosphere in the true sense.
Rocks are not just boring stones; they are the source of our gold, our coal, and even our fertile soil! We live in the "biosphere" because we need air and water just as much as we need the rocky ground.
Teacher's Tip: Correction: Extrusive rocks cool FAST, making SMALL crystals.
Exam Tip: For part 4, mention that "all three layers" (air, water, land) are needed for life.

Question 17: Distinguish between Intrusive and Extrusive Rocks :
Answer: Intrusive Rocks :
1. Intrustive rocks are formed beneath the surface of the Earth.
2. These rocks have large size crystals due to slow cooling.
3. These are also known as plutonic rocks.
4. Granite is an example of these rocks.
Extrusive Rocks :
1. Extrusive rocks are formed on the surface of the Earth.
2. Crystals are not formed due to rapid cooling of lava.
3. These are also known as volcanic rocks.
4. Basalt is an example of these rocks.
Think of this as "Deep Rocks" vs "Surface Rocks." Intrusive rocks are like buried treasure with big shiny crystals, while Extrusive rocks are dark, dense volcanic stones.
Teacher's Tip: In-side vs Ex-it!
Exam Tip: Creating a table for this comparison is the best way to score full marks.