Living Science Chemistry Class 6 ICSE Solutions Chapter 8 Rocks and Minerals

ICSE Living Science Chemistry for Class 6 Solutions Chapter 8 Rocks and Minerals

Check Your Progress

Answer these questions.
Question 1.
What is lithosphere ?
Answer:
The solid crust of rocks that form the surface of the earth is called lithosphere.

Question 2.
Give three examples of igenous rocks.
Answer:
Granite, pumice, basalt

Question 3.
Give three examples of sedimentary rocks.
Answer:
Sandstone, limestone, coal

Question 4.
Which two rocks can get metamorphosed into schist ?
Answer:
Basalt (an igneous rock) and shale (a sedimentary rock)

Check Your Progress

Answer the questions.
Question 1.
Malachite and copper pyrites are the ores of an important metal. Name the metal.
Answer:
Copper

Question 2.
Name a non-metallic mineral used to make glass and cement.
Answer:
Lime (Quicklime)

Question 3.
Name two organic minerals.
Answer:
Petroleum and coal

Question 4.
Name the impurity which gives red colour to a ruby.
Answer:
Chromium

A. Tick the most appropriate answer.

Question 1.
Which of the following is a sedimentary rock ?
a. Obsidian
b. Conglomerate
c. Marble
d. Pumice
Answer:
b. Conglomerate

Question 2.
The metamorphic rock formed from limestone is
a. marble
b. gneiss
c. quartzite
d. slate
Answer:
a. marble

Question 3.
Haematite is an ore of
a. copper
b. iron
c. aluminium
d. mercury
Answer:
b. iron

Question 4.
Which of the following is an ore that contains aluminium?
a. Bauxite
b. Malachite
c. Galena
d. Cinnabar
Answer:
a. Bauxite

Question 5.
Which of the following does not contain calcium ?
a. Lime
b. Chalk
c. Gypsum
d. Talc
Answer:
d. Talc

B. Fill in the blanks.

Question 1.
The solid crust of rocks forming the surface of the earth is called
Answer:
The solid crust of rocks forming the surface of the earth is called lithosphere.

Question 2.
Granite is a/an rock.
Answer:
Granite is an igneous rock.

Question 3.
Sandstone is a/an rock
Answer:
Sandstone is a sedimentary rock.

Question 4.
A ……….. is a naturally occurring substance which contains elements or their compounds.
Answer:
A mineral is a naturally occurring substance which contains elements or their compounds.

Question 5.
Traces of ……………. give ruby its bright red colour.
Answer:
Traces of chromium give ruby its bright red colour.

Question 6.
…………….. and are known as fossil fuels.
Answer:
Coal, petroleum and natural gas are known as fossil fuels.

C. State if the following statements are true or false. Correct the statement if it is false.

Question 1.
Extrusive igneous rocks are formed by the cooling of magma below the earth’s surface.
Answer:
False. Intrusive igneous rocks are formed by the cooling of magma below the earth’s surface.

Question 2.
Limestone is an igenous rock.
Answer:
False. Limestone is a sedimentary rock.

Question 3.
Marble is formed by the metamorphosis of sandstone.
Answer:
False. Marble is formed by the metamorphosis of limestone.

Question 4.
Talc is the softest mineral.
Answer:
True

Question 5.
Quartz and mica are metallic minerals.
Answer:
False. Quartz and mica are non-metallic minerals.

Question 6.
To detect leakage of LPG, ethyl alcohol is added to it.
Answer:
False. To detect leakage of LPG, ethyl mercaptan is added to it. ‘

D. Match the following.

Column A	Column B
1. Malachite	a. hardest substance
2. Diamond	b. Copper
3. Talc	c. sedimentary rock
4. Granite	d. magnesium silicate
5. Rust	e. igneous rock
6. Quartzite	f. metamorphic rock
	g. iron

Answer:

Column A	Column B
1. Malachite	b. Copper
2. Diamond	a. hardest substance
3. Talc	d. magnesium silicate
4. Granite	e. igneous rock
5. Rust	c. sedimentary rock
6. Quartzite	f. metamorphic rock

E. Classify the following rocks according to their types.
1. Basalt
2. Schist
3. Gneiss
4. Pumice
Answer:
1. Basalt – Igneous rock
2. Schist – Metamorphic rock
3. Gneiss – Metamorphic rock
4. Pumice – Igneous rock

F. Give the chemical name and the metal extracted from the following ores.

1. Haematite
2. Bauxite
3. Galena
4. Cinnabar
Answer:
1. Haematite –
Chemical name – Iron oxide
Metal extracted – Iron

2. Bauxite –
Chemical name – Hydrated aluminium oxide
Metal extracted – Aluminium

3. Galena –
Chemical name – Lead sulphide
Metal extracted – Lead

4. Cinnabar –
Chemical name – Mercury sulphide
Metal extracted – Mercury

G. Name the following

1. An ore of silver
2. A mineral containing copper carbonate
3. Chemical name of galena
4. Chemical name of rock salt
Answer:
1. An ore of silver – Argentite (silver sulphide)
2. A mineral containing copper carbonate – Malachite
3. Chemical name of galena – Lead sulphide
4. Chemical name of rock salt – Sodium chloride

H. Define the following terms.
1. Mineral
2. Ore
3. Gemstone
4. Fossil
5. Fossil fuels
Answer:
1. Mineral : A mineral is a naturally occuring substance which contains elements or their compounds.
2. Ore : The minerals from which metals can be extracted conveniently and economically are called as ores.
3. Gemstone: A gemstone (or gem) is a piece of mineral which is used to make jewellery.
4. Fossil : Fossils are the remains of prehistoric plants and animals buried under the earth millions of years ago.
5. Fossil fuels : Fossil fuels are the fuels which are formed by the decay and decomposition of the remains of dead plants and animals, buried under the earth millions of years ago. Coal, petroleum and natural gas are known as fossil fuels.

I. Give the chemical name and one use of the following minerals.

1. Rock salt
2. Lime
3. Plaster of Paris
1. Rock star
Answer:
Chemical name of rock salt is sodium chloride.
Use – It is used in cooking, to preserve pickles, meat, etc. Is also used to manufacture baking powder, washing soda, etc.

2. Lime –
Answer:
Chemical name of lime is calcium oxide.
Use – It is used in agriculture to neutralize acidic soil. Is also used for making glass, cement and for whitewashing.

3. Plaster of Paris –
Answer:
Chemical name of Plaster of Paris is calcium sulphate hemihydrate.
Use – It is used for plastering fractured bones, making casts for statues, decorative work on walls and ceilings.

J. Differentiate between the following.

1. Sandstone and conglomerate
2. Slate and marble
3. Rocks and minerals

Question 1.
Sandstone and conglomerate
Answer:
Sandstone is a sedimentary rock formed by deposits of sand. It consists of maimy quartz of various colours and hence, is tan, brown, yellow, red or grey in colour. Sandstone is used as a building and paving material. Hard sandstone is an excellent material to make grindstones for sharpening blades. Conglomerate is a sedimentary rock formed by cementing together of round pebbles such as those in the river beds. It is also called as pudding stone because of the mixture of rock materials in it. It is mostly orange in colour.

Question 2.
Slate and marble
Answer:

1. Slate is a metamorphic rock formed from shale (sedimentary rock) while marble is a metamorphic rock formed from limestone (sedimentary rock).
2. Slate is usually grey in colour while marble is usually white, black, grey or pink.
3. Slate is extensively used for making blackboards and also for the roofing of buildings while marble is used for making statues and for construction of buildings.

Question 3.
Rocks and minerals
Answer:

1. Minerals are naturally occurring solids formed through geological processes while a rock is a mixture of various minerals.
2. Minerals have a definite chemical composition by which they can be identified while a rock may not have a specific chemical composition.
3. Minerals are classified as metallic, non-metallic and organic minerals while rocks are classified as igneous, sedimentary and metamorphic rocks.

K. Answer the following in short.

Question 1.
Name the three types of rocks.
Answer:
Igneous rocks, sedimentary rocks and metamorphic rocks.

Question 2.
What are igneous rocks ? Give two examples.
Answer:
Igneous rocks are rocks formed by the cooling, solidification and crystallization of the magma and lava of volcanic eruptions. Since, they are the first rocks to be formed, they are also called as primary rocks. They are generally hard, have no layers, do not contain fossils and are crystalline and non- porous.
Examples : Granite, pumice, tuff, basalt.

Question 3.
Why are sedimentary rocks also called secondary rocks?
Answer:
Sedimentary rocks are also called as secondary or derived rocks as the material (clay or sand, etc.) they are formed from is derived from other rocks (igenous/primary).

Question 4.
What are metamorphic rocks ? Give two examples.
Answer:
Metamorphic rocks are rocks formed when igneous and sedimentary rocks are subjected to high temperature and pressure. They are harder and more compact than its original type. Examples : Gneiss, slate, marble, quartzite, schist.

Question 5.
Why are fossil fuels called non-renewable resources ?
Answer:
Fossil fuels take millions of years to form inside the earth’s crust. Their reserve is limited and cannot be regenerated as fast as they are being used up. They will eventually run out ‘ kissed in great amount. Hence, fossil fuels are considered as non-renewable resources.

L. Answer the following in detail.

Question 1.
Explain the formation of sedimentary rocks.
Answer:
Sedimentary rocks are formed by the sediments, particles, grains or fragments derived from previously existing primary rocks. The action of wind and water (weathering) breaks up the primary rocks into smaller particles such as clay or sand.

These particles are carried by running water and eventually settle at the bottom of lakes, rivers, seas and oceans layer by layer as a sediment. Over a period of time, the sediments thicken as more material is added to them and under pressure transform into a hard rock called sedimentary rock. They are also called a secondary or derived rocks as the material is derived from other rocks. These are also known as stratified rocks because the layers of sediments known as strata are formed during the formation of these rocks.

Question 2.
Explain the rock cycle.
Answer:
Rocks forming the crust of the earth change from one type of another due to various processes. This change of rocks from one type to another is called the rock cycle.

Rock cycle :
Metamorphic rock : Both igneous and sedimentary rocks were subjected to pressure and heat and they were converted into metamorphic rocks.

Igenous rock :
The first rocks forming the crust of the earth were the igneous rocks. metamorphic rock.

Sedimentary rock : Various agents of degradation eroded the igenous rocks and these eroded materials were deposited at the bottom of rivers and seas and were transformed to sedimentary rocks.

Question 3.
How many types of minerals are there ? Explain with examples.
Answer:
Minerals are obtained from different rocks and classified into three categories.

1. Metallic minerals – These are minerals which contain metallic substances. Most of the metallic minerals of iron, copper, aluminium, lead, zinc and gold are obtained from igneous or metamorphic rocks.
2. Non-metallic minerals – These are minerals which contain non-metallic substances. Examples : Talc, sand, quartz, mica and gypsum.
3. Organic minerals – Minerals like coal and petroleum are organic minerals. They are generally found in sedimentary rocks.

Question 4.
How is coal formed ? Name the different varieties of coal.
Answer:
Coal is formed by the decay and decomposition of large plants that were buried under the earth millions of years ago. Due to high temperature and high pressure inside the earth and in the absence of air, the plants got converted into coal. Coal is classified into four main types. Coal with high carbon content gives out large amount of heat energy on burning.
Type – Carbon content
Li-nite – 25 – 35%
Sub-bituminous coal – 35 – 45%
Bituminous coal – 45 – 86%
Anthracite – 86 – 98%

Question 5.
How is petroleum formed ? Name the main products obtained from crude oil by fractional distillation.
Answer:
Petroleum means rock oil (petra = rock, oleum = oil). It is formed by the decay and decomposi tion of the remains of marine plants and animals that were buried under the seabed millions of years ago. Under high temperature and pressure, in the absence of air, these remains of plants and animals changed into petroleum and natural gas. The petroleum thus formed got trapped between the layers of impervious rocks (non-porous rocks) forming an oil trap.

Petrolium or cmde oil is a complex mixture of several solid, liquid and gaseous substances mixed with water, salt and silt (fine clay). The main products obtained by the fractional distillation of petroleum are : petroleum gas, petrol, diesel, kerosene, fuel oil, lubricating oil, paraffin wax, asphalt, etc.

M. Give reasons for the following.

Question 1.
Many pumice rocks float in water.
Answer:
Pumice is a porous rock which is formed when lava cools quickly above the ground. It has many tiny pores which are formed by gases trapped inside them at the time of formation. These rocks are so light that many pumice rocks actually float on water.

Question 2.
Sedimentary rocks are formed in layers.
Answer:
The sediments or particles settle at the bottom of lakes, seas, oceans and rivers layer by layer and over a period of time, under pressure, transform into sedimentary rock. Hence, the layers of sediments are formed during the formation of these rocks, and these rocks contain layers.

Living Science Chemistry Class 6 ICSE Solutions