Minerals and Rocks Class 11 Important Extra Questions Geography Chapter 5
Minerals and Rocks Important Extra Questions Very Short Answer Type
Question 1.
What is meant by smelting?
Answer:
The process through which metals are separated from ores by using heat is called smelting.
Question 2.
Why are coal and petroleum called fossil fuels?
Answer:
Because they are associated with fossils (remnants of organisms).
Question 3.
Name two important sources of atomic energy found in India.
Answer:
Uranium and Thorium.
Question 4.
Define a rock.
Answer:
A rock is any natural mass of mineral matter that makes up the earth’s crust.
Question 5.
Name the types of rocks.
Answer:
The three types of rocks are the igneous rocks, the sedimentary rocks and the metamorphic rocks. ‘
Question 6.
Which are two main types of igneous rocks?
Answer:
On the basis of chemical differentiation of magma, there are two types of igneous rocks, viz., mafic and felsic.
Question 7.
What is meant by ‘texture? of the rocks?
Answer:
Texture relates to the sizes and patterns of the mineral crystals present in the rock.
Question 8.
Name the scale that grades between the size of mineral grains.
Answer:
The system of grading of mineral grains according to their size is called the Wentworth scale.
Question 9.
What is ‘phenocrysts’?
Answer:
Few large crystals embedded in a matrix of smaller crystals are known as phenocrysts.
Question 10.
What is ‘diagenesis’?
Answer:
It is the process of physical and chemical changes affecting sediments during their conversion into solid rocks.
Question 11.
What is the scientific study of rocks called?
Answer:
The scientific study of rocks is called petrology.
Question 12.
What does the term ‘lithosphere’ mean?
Answer:
The term lithosphere means a sphere of rocks.
Question 13.
Give two examples of soft rocks.
Answer:
Clay and chalk.
Question 14.
What kind of rock is granite?
Answer:
Granite is a coarse-grained igneous rock that is formed by the slow cooling of magma.
Question 15.
What happens to clay when it gets metamorphosed?
Answer:
It converts into slate.
Question 16.
What is metamorphism?
Answer:
Metamorphism is the change of form. It refers to the change in the form of rock when it is subjected to heat or pressure.
Question 17.
How many minerals have been identified and named till date?
Answer:
At least 2000 minerals have been named and identified till date.
Question 18.
Name the largest diamond ever found.
Answer:
Cullinan diamond is the largest diamond ever found.
Question 19.
What is the basic source of all minerals found in the earth?
Answer:
The basic source of all minerals is the hot magma in the interior of the earth.
Question 20.
What are ‘optical properties’ of minerals?
Answer:
Optical means ‘usual’. The optical properties of minerals are evaluated by means of a microscope using polarised light rays.
Question 21.
What are sedimentary rocks?
Answer:
The rocks which are formed by the accumulation of sediments are called sedimentary rocks.
Question 22.
Name three types of sedimentary rocks on the basis of their mode of formation.
Answer:
Mechanically formed,
Organically formed,
Chemically formed.
Question 23.
Name the different types of coal.
Answer:
Peat, Lignite, Bituminus and Anthracite.
Question 24.
What is the thickness of lithosphere?
Answer:
The thickness of the lithosphere is about 100 km.
Question 25.
What are schists?
Answer:
Strongly developed foliation is known as schists.
Minerals and Rocks Important Extra Questions Short Answer Type
Question 1.
What is lithification?
Answer:
The fragments of the rocks are transported by various exogenous agencies and deposited. These deposits through compaction and/or cementation turn into rocks. This process is called lithification. In many sedimentary rocks, the layers of deposits. retain their characteristics even after lithification.
Question 2.
How would you classify the igneous rocks based on the size and nature of crystals?
Answer:
There are five types of igneous rocks based on the size and nature of crystals viz.
rocks with phaneritic textured crystals
rocks with orphan textured crystals
equigranular textured rocks, and
porphyritic textured rocks.
The crystals large enough to be seen with naked eyes or with the help of hand lens are called phaneritic textured crystals, whereas those too small to be distinguished without the aid of a microscope are – called orphan textured crystals of the igneous rocks. Where crystals in the rocks are all within the same size range, the texture is described as equigranular, whereas few large crystals are embedded in a matrix of smaller crystals, the texture is porphyritic.
Question 3.
Discuss the classification of sedimentary rocks into clastic and non-clastic division.
Answer:
Clastic means ‘broken’, describes clastic sediments consisting of particles removed individually from a parent rock source. The naming of clastic rocks depends on the size of component mineral grains.
The non-clastic sedimentary rocks are made of sediments of two basic types: chemical precipitates and organically derived sediments.
The chemical precipitates are solid mineral matters precipitated from an aqueous solution. The rock salt and gypsum are its examples. The organically derived sediments consist of remains of plants and animals as well as mineral matters produced by activities of plants and animals. Coal and limestone are examples.
Question 4.
What are schists?
Answer:
As metamorphism continues a large percentage of the minerals assume the plate-like shape and are assembled in parallel orientation in the rock, a structure is known as foliation. Strongly developed foliation is known as schist.
Question 5.
What is meant by mineral hardness?
Answer:
The degree to which a mineral surface resists being scratched is known as its mineral hardness. Hardness is important because it determines how a mineral is worn away by the abrasive action of stream, waves, wind and glaciers in the processes of erosion and transportation.
Question 6.
What are minerals and how are they formed?
Answer:
The mineral is a naturally occurring homogeneous solid that is an inorganic substance having an orderly atomic structure and definite chemical composition.
The basic source of all minerals is hot magma in the interior of the earth. When magma cools, crystals of mineral appear. These first crystals may sink in the magma so that the composition of the magma changes with depth. Thus, a sequence of minerals is formed in the rocks as the magma cools. Besides this, certain minerals such as coal, petroleum and natural gas are organic substances found in solid, liquid and gaseous forms respectively.
Question 7.
Describe the formation of sedimentary rocks.
Answer:
Sedimentary rocks are made from sediments deposited by the erosion and weathering of other rocks. Wind, water and snow erode rocks and carry the sediments to low lying areas. When deposited in the sea, they are compressed and hardened to form layers of rocks. Sediment is a fragmented mineral and organic matter derived directly or indirectly from pre-existing rocks and from life processes transported and deposited by air, water, etc. Chalk, sandstone, limestone, gypsum and coal are the examples.
Question 8.
What is mineral ‘lustre’?
Answer:
The appearance of a mineral surface under reflected light is referred to as its mineral lustre. It is described by several descriptive adjectives, such as metallic (metal like), adamantine (diamond), vitreous glass), resinous (oil), pearly or silky.
Question 9.
What do you understand by the specific gravity of minerals?
Answer:
Each mineral has a certain specific gravity. The specific gravity is the ratio of its density to the density of water at 4° Celsius. Mineral’s specific gravity is a property of great importance because it determines the density of a given rock and rock density, in turn, determines the gross layered structure of the earth.
Question 10.
What is the Deccan Trap?
Answer:
The Deccan trap is an extensive area in the north-west part of India. It covers about 5 lakh sq. km, area. It has been formed by lava flows. Lava has solidified to form basalt. It is useful for cotton cultivation.
Question 11.
How is coal formed?
Answer:
Vegetation is hurried in swamps and forests. Due to pressure of the overlying sediments, the remains of plants are changed into carbon. Coal is formed in this way. Coal is of different types such as peat, lignite, bituminous and anthracite.
Question 12.
What are the three types of rocks? Give two examples of each of them.
Answer:
The three types of rocks are:
Igneous rocks
Sedimentary rocks
Metamorphic rocks
1. Igneous rocks: These rocks are formed by the cooling and solidification of molten lava and magma in the interior of the earth. Granite and basalt are examples.
2. Sedimentary rocks: These rocks have been formed by the deposition cementation of the fragments by exogenous means, i.e., wind, ice and sea. Examples are – sandstone and clay.
3. Metamorphic rocks: These rocks are formed by the change in colour, hardness, texture and mineral composition of the pre-existing rocks. Examples are – marble, slate.
Question 13.
What is meant by the texture of rocks?
Answer:
The texture means the size and pattern of the mineral crystals present in the rock. The size of the mineral crystals in an igneous rock depends largely upon the rate of cooling of magma.
Question 14.
Why fossils are preserved in sedimentary and not in igneous rocks?
Answer:
Sedimentary rocks are formed by the deposition of fragments ‘ carried away by exogenous means. They are deposited in distinct strata or layers. Fossils in the form of prints of leaves, insects or soft bovine animals and pieces of bones, shells or some hard parts of old living beings are embedded into layers of the sedimentary rocks. Thus, fossils are preserved in sedimentary rocks. The igneous rocks are formed by the solidification of magma. They are massive. They have no layers. Therefore, fossils cannot be preserved in igneous hard rocks and they are fossils-free.
Minerals and Rocks Important Extra Questions Long Answer Type
Question 1.
Write short notes on:
1. Sedimentary rocks
2. Types of metamorphism
Answer:
1. Sedimentary rocks: Exogenous agencies such as rain, wind, ice, running water, plants and animals are constantly hurried in rock disintegration producing loose and broken rock fragments in all sizes. These minerals are carried by wind, ice and running water in depressions such as lakes and seas on the earth’s surface. Such dropped materials are called sediments. Accumulation of these sediments in course of time gives rise to sedimentary rocks. The word ‘sedimentary’ is derived from the Latin word ‘sedimented’ means setting down. The sediments are usually deposited in distinct layers or strata. Therefore, these rocks are also known as stratified rocks.
2. Types of metamorphism: Metamorphism is the process of transformation of pre-existing rock into a new rock. Thus, metamorphic rocks are found when a rock is subjected to heat and/or pressure. Their characteristics are altered by forming new mineral forms. There are three types of metamorphism, viz. foliation, lineation and banding. When, under continued metamorphism, its minerals assume the plate-like shape and are assembled in parallel orientation in the rock, it is called foliation, e.g., Schist is formed in this manner.
When the mineral grains are drawn out into long, thin, pencil-like objects, all in parallel alignment, it is referred to as lineation. In another type of metamorphism, i.e., banding, the minerals of different varieties or groups are segregated into alternate layers. These layers are usually of light or dark shades, making the banding conspicuous.
Question 2.
What is the economic importance of minerals?
Answer:
Mineral resources can be divided into four main groups – essential resources, energy resources, metal resources and industrial resources. The most basic group, essential resources, comprises soil and water. Energy resources can be divided into fossil fuels (crude oil, natural gas, coal, oil shale and tar sand) and nuclear fuels (uranium, thorium and geothermal power). Metal resources range from structural metals such as iron, aluminium and titanium to ornamental and industrial metals such as gold, platinum and gallium.
Mineral deposits have two geological characteristics that make them a real challenge to modem civilization. First, all of them are non-renewable resources. The geological processes that form them are much slower than the rate at which we exploit them. There is no likelihood of our ability to grow mineral deposits at a rate equal to our consumption. Second, mineral deposits have a place value. We cannot decide from where to extract them; nature made that decision for us when the deposits were formed.
Question 3.
Describe the categorization of metamorphic rocks.
Answer:
The metamorphic rocks can be broadly grouped into two major classes – cataclastic rocks and recrystallised rocks. Cataclastic rocks are formed by mechanical disruption (breaking and crushing) of the original materials. The process is described as dynamic metamorphism.
The recrystallised rocks are further divided into two sub-classes – contact and regional metamorphic rocks. The contact metamorphic rocks are formed by recrystallisation under high temperature caused by intruding magma. The rocks are not subjected to bending or breaking and new minerals emanating from magma are added to metamorphosed rocks. The regional metamorphic rocks undergo recrystallisation during the process of being deformed by sharing often under the condition of high pressure or high temperature or bolts.
Question 4.
Discuss various types of rocks in detail.
Answer:
There are three main groups of rocks: igneous, sedimentary and metamorphic rocks.
Igneous rocks: These are formed from lava hurled out of a volcano or from the cooling of hot magma below the crust. Granite is a coarse-grained rock that was formed by the slow cooling of magma. Basalt is a fine-grained igneous rock, almost black, that was formed by quick cooling of lava. Chemical differentiation of magma gives rise to mafic and felsic types of igneous rocks.
The size of mineral crystals in an igneous rock largely depends upon the rate of cooling of magma. As a general rule, rapid cooling results in small crystals and slow cooling in large crystals. Extremely sudden cooling results in the formation of a natural glass which is non-crystalline. Large bodies of magma trapped beneath the surface cool very slowly because the surrounding rocks conduct the heat slowly. Rapid cooling occurs in lava that loses heat rapidly to the atmosphere or to the overlying ocean water.
Question 5.
Describe the formation of igneous rocks, giving suitable examples of various types.
Answer:
The igneous rocks are divided into extrusive rocks and intrusive rocks. When the magma solidifies on the surface of the earth, we call it an extrusive rock. A typical example of this kind of rock is basalt. It is a very fine-grained rock, usually Sf black in colour.
On the other hand, when the magma solidifies in the crust, below the surface, it is called an intrusive rock. The few most common examples of intrusive rocks are granite and dolerite. More frequent, however, is the solidification of magma below the earth’s surface leading to the formation of intrusive rocks. Igneous rocks are classified on the basis of chemical composition and texture. Chemical differentiation of magma gives rise to mafic and felsic types of igneous rocks.
Texture relates to the sizes and pattern of the mineral crystals present in the rock. The size of mineral crystals in an igneous rock depends largely upon the rate of cooling of magma. As a general rule, rapid cooling results in small crystals and slow cooling results in large crystals. Extremely sudden cooling results in the formation of natural glass which is non-crystalline. Large bodies of magma trapped beneath the surface cool very slowly because the surrounding rocks conduct the heat slowly. Rapid cooling occurs in lava that loses heat rapidly to the atmosphere or to the overlying ocean water.
