Multiple choice question.
Which one of the following are the two main constituents of granite?
A. Iron and nickel
B. Iron and silver
C. Silica and aluminium
D. Iron Oxide and potassium
The composition of granite is typically 70-77% silica, 11-13% aluminium.
Multiple choice question.
Which one of the following is the salient feature of metamorphic rocks?
A. Changeable
B. Quite
C. Crystalline
D. Foliation
The word metamorphic means ‘change of form’. These rocks undergo recrystallisation and reorganisation of materials within the original rocks.
Multiple choice question.
Which one of the following is not a single element mineral?
A. Gold
B. Silver
C. Mica
D. Graphite
The general formula of mica is XY2-3Z4O10(OH,F)2 where X= K, Na, Ba, Ca, Cs; Y= Al, Mg, Fe2+; Z= Si, Al, Fe3+
Multiple choice question.
Which one of the following is the hardest mineral?
A. Topaz
B. Diamond
C. Quartz
D. Feldspar
Diamond is the hardest material because of its cage like structure.
Multiple choice question.
Which one of the following is not a sedimentary rock?
A. Tillite
B. Borax
C. Breccia
D. Marble
Marble is a metamorphic rock. It undergoes metamorphism.
Answer the following questions in about 30 words.
(i) What do you mean by rocks? Name the three major classes of rocks.
(ii) What is an igneous rock? Describe the method of formation and characteristics of igneous rock.
(iii) What is meant by sedimentary rock? Describe the mode of formation of sedimentary rock.
(iv) What relationship explained by rock cycle between the major type of rock?
(i) A rock can be defined as an aggregate of minerals that forms a more or less definite unit of the lithosphere. It is a consolidated and compact mass of more than two minerals.
On the basis of their mode of formation, rocks can be classified into the following categories:-
• Igneous Rocks (Primary Rocks)
• Sedimentary Rocks (Secondary rocks)
• Metamorphic Rocks.
(ii) The word ‘igneous’ means ‘ire’ derived from the Latin word ‘ignis’ or Sanskrit word ‘agni’.
Igneous rocks are of thermal origin and are formed by the process of solidification of molten rock material called magma. Such molten magma originates from the interior of the Earth. Such magma erupts during volcanic eruptions and on reaching the Earth’s surface, gets solidified by cooling. So they are referred to as primary rocks.
Characteristics of Igneous rocks:-
• Formed by cooling and solidification of Lava
• Hard in nature
• Crystalline and have texture
• Non-porous rock.
(iii) Sedimentary is derived from a Latin word which means ‘settling down’- ‘sedimentum’. Sedimentary rocks are called secondary rocks or derived rocks because they are derived by the denudation of other pre-existing primary or parent rocks.
Sedimentary rocks are formed by denudation, weathering, erosion, transportation and deposition. These consolidated layered strata are known as stratified rocks. Lithification is the cementation, compaction, and hardening of sediments into sedimentary rocks. As the sediments are deposited in water bodies, they get sorted out according to their size. These sediments accumulate in different layers or strata arranged one above the other and thus form sedimentary rocks.
Characteristics of Sedimentary rocks:
• They accumulate in different strata one above the other and thus called stratified rocks.
• Presence of plants and animals between layers of sediments i.e. fossils.
• Formed by agents of denudation.
• Derived from pre-existing primary or parenting rock.
(iv) The changing of the forms of rocks from one to another is known as rock cycle. The changes of these rocks are interrelated. Igneous rocks are primary rocks and it can be changed to form sedimentary or metamorphic rocks. Normally sedimentary rocks form from igneous rocks. These sedimentary rocks themselves can turn into fragments and form another type of sedimentary rocks. The crustal rocks can once again carry down to mantle of the earth by subjugation process and again melt in lava. This lava while erupting will again form igneous rocks and so on.
Answer the following questions in about 150 words.
(i) Define the term ‘mineral’ and name the major classes of minerals with their physical characteristics.
(ii) Describe the nature and mode of origin of the chief types of rock at the earth’s crust. How will you distinguish them?
(iii) What are metamorphic rocks? Describe the types of metamorphic rock and how are they formed?
(i) Minerals are naturally occurring solid inorganic substances having definite chemical composition and physical properties. They are generally crystalline in appearance. Minerals are homogeneous in form while rocks are heterogeneous in their composition. There are atleast 2000 types of minerals that are named and identified in the Earth’s crust.
The classes of minerals are as follows:-
• Feldspar- It is one of the widely spread minerals. Silicon and oxygen are the two common elements. It is used for ceramics and gloss making
• Quartz- It consists of silica and forms one of the most important components of sand and granite. It is white and colourless and used in radio and radar.
• Pyroxene- It consists of calcium, magnesium, aluminium, iron and silica. It is of black and green colour
• Amphibole- It forms about 7% of the earth’s crust and consists of mainly aluminium, silica, iron, magnesium. It is used in asbestos industry.
• Mica- It consists of potassium, aluminium, magnesium, iron, silicon etc and forms 4% of the earth’s crust. It is found in igneous and metamorphic rocks and is used in electrical instruments.
• Olivine- Magnesium, iron, silica are the main elements. It is found in rocks.
(ii) There are three chief types of rocks at the earth’s crust:
• Igneous Rock- The word ‘igneous’ means ‘ire’ derived from the Latin word ‘ignis’ or Sanskrit word ‘agni’. Igneous rocks are of thermal origin and are formed by the process of solidification of molten rock material called magma. Such molten magma originates from the interior of the Earth. Such magma erupts during volcanic eruptions and on reaching the Earth’s surface, gets solidified by cooling. So they are referred to as primary rocks. They are hard and crystalline in nature and have various textures according to the shape and size.
• Sedimentary Rocks- Sedimentary rocks are called secondary rocks or derived rocks because they are derived by the denudation of other pre-existing primary or parent rocks. Sedimentary rocks are formed by denudation, weathering, erosion, transportation and deposition. These consolidated layered strata are known as stratified rocks. Lithification is the cementation, compaction, and hardening of sediments into sedimentary rocks. As the sediments are deposited in water bodies, they get sorted out according to their size. These sediments accumulate in different layers or strata arranged one above the other and thus form sedimentary rocks. They accumulate in different strata one above the other and thus called stratified rocks. Presence of plants and animals between layers of sediments i.e. fossils.
• Metamorphic Rocks- Metamorphic rocks are those which are formed by the process of metamorphism or alteration of pre-existing rocks. Metamorphism means change of form which may be physical or chemical or both. Such metamorphism occurs when rocks are subjected to high temperature, pressure or both. During the process of metamorphism, the original minerals get altered and new minerals are formed. They combine together to form rocks which are harder and more resistant than the original rocks. They are the source to many important mineral deposits.
(iii) The word ‘metamorphic’ means change of form. Metamorphic rocks are those which are formed by the process of metamorphism or alteration of pre-existing rocks. Such metamorphism occurs when rocks are subjected to high temperature, pressure or both. During the process of metamorphism, the original minerals get altered and new minerals are formed. They combine together to form rocks which are harder and more resistant than the original rocks. They are the source to many important mineral deposits like marble slates, mica, phyllites. Metamorphic rocks have their minerals arranged in a series of bands called foliation.
There are two types of metamorphic rocks:-
• Foliated metamorphic rocks- These rocks have a layer of banded appearance that is produced by exposure to heats and direct pressure. Example- slate, phyllites.
• Non-Foliated metamorphic rocks- These types of rocks have no foliation or any appearance and thus they are subjected to heat and pressure. Example- Marble, Quartzite.