Q 1 – What is meant by smelting?
Ans. The process through which metals are separated from ores by using heat is called smelting.
Q 2 – Why are coal and petroleum called fossil fuels?
Ans. Because they are associated with fossils (remnants of organisms)
Q 3 – Name two important sources of atomic energy found in India.
Ans. Uranium and Thorium.
Q 4 – Define a rock.
Ans. A rock is any natural mass of mineral matter that makes up the earth’s crust.
Q 5 – Name the types of rocks
Ans. The three types of rocks are the igneous rocks, the sedimentary rocks and the metamorphic rocks. ‘’
Q 6 – Which are two main types of igneous rocks?
Ans. On the basis of chemical differentiation of magma, there are two types of igneous rocks, viz., mafic and felsic.
Q 7 – What is meant by ‘texture? of the rocks?
Ans. Texture relates to the sizes and patterns of the mineral crystals present in the rock.
Q 8 – Name the scale that grades between the size of mineral grains.
Ans. The system of grading of mineral grains according to their size is called the Wentworth scale.
Q 9 – What is ‘phenocrysts’?
Ans. Few large crystals embedded in a matrix of smaller crystals are known as phenocrysts.
Q 10 – What is ‘diagenesis’?
Ans. It is the process of physical and chemical changes affecting sediments during their conversion into solid rocks.
Q 11 – What is the scientific study of rocks called?
Ans. The scientific study of rocks is called petrology.
Q 12 – What does the term ‘lithosphere’ mean?
Ans. The term lithosphere means a sphere of rocks.
Q 13 – Give two examples of soft rocks.
Ans. Clay and chalk.
Q 14 – What kind of rock is granite?
Ans. Granite is a coarse-grained igneous rock that is formed by the slow cooling of magma.
Q 15 – What happens to clay when it gets metamorphosed?
Ans. It converts into slate.
Q 16 – What is metamorphism?
Ans. Metamorphism is the change of form. It refers to the change in the form of rock when it is subjected to heat or pressure.
Q 17 – How many minerals have been identified and named till date?
Ans. At least 2000 minerals have been named and identified till date.
Q 18 – Name the largest diamond ever found.
Ans. Cullinan diamond is the largest diamond ever found.
Q 19 – What is the basic source of all minerals found in the earth?
Ans. The basic source of all minerals is the hot magma in the interior of the earth.
Q 20 – What are ‘optical properties’ of minerals?
Ans. Optical means ‘usual’. The optical properties of minerals are evaluated by means of a microscope using polarised light rays.
Q 21 – What are sedimentary rocks?
Ans. The rocks which are formed by the accumulation of sediments are called sedimentary rocks.
Q 22 – Name three types of sedimentary rocks on the basis of their mode of formation.
- Ans. Mechanically formed,
- Organically formed,
- Chemically formed.
Q 23 – Name the different types of coal.
Ans. Peat, Lignite, Bituminus and Anthracite.
Q 24 – What is the thickness of lithosphere?
Ans. The thickness of the lithosphere is about 100 km.
Q 25 – What are schists?
Ans. Strongly developed foliation is known as schist
Q 26 – What is lithification?
Ans. 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.
Q 27 – How would you classify the igneous rocks based on the size and nature of crystals?
Ans. 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.
Q 28 – Discuss the classification of sedimentary rocks into clastic and non-clastic division
Ans. 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.
Q 29 – What are schists?
Ans. 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.
Q 30 – What is meant by mineral hardness?
Ans. 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.
Q 31 – What are minerals and how are they formed?
Ans. 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.
Q 32 – Describe the formation of sedimentary rocks.
Ans. 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.
Q 33 – What is mineral ‘lustre’?
Ans. 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.
Q 34 – What do you understand by the specific gravity of minerals?
Ans. 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.
Q 35 – What is the Deccan Trap?
Ans. 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.
Q 36 – How is coal formed?
Ans. 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.
Q 37 – What are the three types of rocks? Give two examples of each of them.
Ans. 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.
Q 38 – What is meant by the texture of rocks?
Ans. 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.
Q 39 – Why fossils are preserved in sedimentary and not in igneous rocks?
Ans. 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.
Q 40 – Write short notes on:
1. Sedimentary rocks
2. Types of metamorphism
Ans. 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.
Q 41 – What is the economic importance of minerals?
Ans. 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.
Q 42 – Describe the categorization of metamorphic rocks.
Ans, 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.
Q 43 – Discuss various types of rocks in detail.
Ans. 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.
Q 44 – Describe the formation of igneous rocks, giving suitable examples of various types.
Ans. 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.
Q 45 – What do you mean by rocks? Name the three major classes of rocks.
Ans. The earth’s crust is composed of rocks. A rock is made up by aggregate of one or more minerals. Rock may be hard or soft and in varied colors. For example, granite is hard, soapstone is soft. Gabbro is black and quartzite can be milky white. Rocks do not have a definite composition of mineral constituents. Feldspar and quartz are the most common minerals found in rocks.
There are many different kinds of rocks which are grouped under three families on the basis of their mode
of formation.
They are:
- Igneous Rocks
- Sedimentary Rocks and
- Metamorphic Rocks.
Q 46 – What is an igneous rock? Describe the method of formation and characteristics of igneous rock.
Ans. The igneous rocks are formed when magma cools and solidifies. Igneous rocks form out of magma and lava from the interior of the earth, therefore, they are known as primary rocks.
Method of formation: When magma in its upward movement cools and turns into solid form it is called igneous rock. The process of cooling and solidification can happen in the earth’s crust or on the surface of the earth. Igneous rocks are classified based on texture. The texture depends upon the size and arrangement of grains or other physical conditions of the materials. If molten material is cooled slowly at great depths, mineral grains may be very large. Sudden cooling (at the surface) results in small and smooth grains. Intermediate conditions of cooling would result in intermediate sizes of grains making up igneous rocks. Granite, gabbro, pegmatite, basalt, volcanic breccia and tuff are some of the examples of igneous rocks.
Features:
- They are made up of solidified lava.
- Liquid lava gets solidified by gradual cooling
- They are compact
- They do not have fossils.
Q 47 – What is meant by sedimentary rock? Describe the mode of formation of sedimentary rock.
Ans. The word ‘sedimentary’ is derived from the Latin word sedimentum, which means settling. All types of rocks of the earth’s surface are exposed to denudational agents, and are broken up into various sizes of fragments. Such fragments are transported by different exogenous agencies and deposited.
These deposits through compaction turn into rocks. This process is called lithification. In many sedimentary rocks, the layers of deposits retain their characteristics even after lithification. Hence, we see a number of layers of varying thickness in sedimentary rocks like sandstone, shale etc.
Q 48 – What relationship explained by rock cycle between the major type of rocks?
Ans. Rocks do not remain in their original form for long but may undergo transformation. Rock cycle is a continuous process through which old rocks are transformed into new ones. Igneous rocks are primary rocks and other rocks (sedimentary and metamorphic) form from these primary rocks. Igneous rocks can be changed into metamorphic rocks. The fragments derived out of igneous and metamorphic rocks form into sedimentary rocks.
Sedimentary rocks themselves can turn into fragments and the fragments can be a source for formation of sedimentary rocks. The crustal rocks (igneous, metamorphic and sedimentary) once formed may be carried down into the mantle (interior of the earth) through subduction process (parts or whole of crustal plates going down under another plate in zones of plate convergence) and the same melt down due to increase in temperature in the interior and turn into molten magma, the original source for igneous rocks.
Q 49 – Define the term ‘mineral’ and name the major classes of minerals with their physical characteristics.
Ans. A mineral is a naturally occurring organic and inorganic substance, having an orderly atomic structure and a definite chemical composition and physical properties. A mineral is composed of two or more elements. But, sometimes single element minerals like sulphur, copper, silver, gold, graphite etc. are found. There are at least 2,000 minerals that have been named and identified in the earth crust; but almost all the commonly occurring ones are related to six major mineral groups that are known as major rock forming minerals.
Some major minerals and their characteristics:
- Feldspar: Silicon and oxygen are common elements in all types of feldspar and sodium, potassium, calcium, aluminium etc. are found in specific feldspar variety.
- Quartz: It is one of the most important components of sand and granite. It consists of silica. It is a hard mineral virtually insoluble in water.
- Pyroxene: Pyroxene consists of calcium, aluminum, magnesium, iron and silica. Pyroxene forms 10 per cent of the earth’s crust.
- Amphibole: Aluminium, calcium, silica, iron, magnesium are the major elements of amphiboles. They form 7 percent of the earth’s crust.
- Mica: It comprises of potassium, aluminium, magnesium, iron, silica, etc. It forms 4 per cent of the earth’s crust.
- Olivine: Magnesium, iron and silica are major elements of olivine. It is used in jewellery. It is usually a greenish crystal, often found in basaltic rocks.
- Metallic Minerals: These minerals contain metal content and can be sub-divided into three types:
- Precious metals,
- Ferrous metals
- Non- ferrous metals.
Q 50 – Describe the nature and mode of origin of the chief types of rock at the earth’s crust. How will you distinguish them?
Ans The earth’s crust is composed of rocks. A rock is made up by aggregate of one or more minerals. Rock may be hard or soft and in varied colours. For example, granite is hard, soapstone is soft. Gabbro is black and quartzite can be milky white. Rocks do not have definite composition of mineral constituents. Feldspar and quartz are the most common minerals found in rocks.
There are many different kinds of rocks which are grouped under three families on the basis of their mode of formation. They are:
- Igneous Rocks
- Sedimentary Rocks and
- Metamorphic Rocks.
- Igneous Rocks: The igneous rocks are formed when magma cools and solidifies. Igneous rocks form out of magma and lava from the interior of the earth, therefore, they are known as primary rocks. When magma in its upward movement cools and turns into solid form it is called igneous rock. Intermediate conditions of cooling would result in intermediate sizes of grains making up igneous rocks. Granite, gabbro, pegmatite, basalt, volcanic breccia and tuff are some of the examples of igneous rocks.
- 2. Sedimentary Rocks: The word ‘sedimentary’ is derived from the Latin word sedimentum, which means ‘settling’. All types of rocks of the earth’s surface are exposed to denudational agents, and are broken up into various sizes of fragments. Such fragments are transported by different exogenous agencies and deposited. These deposits through compaction turn into rocks. This process is called lithification. In many sedimentary rocks, the layers of deposits retain their characteristics even after lithification. Hence, we see a number of layers of varying thickness . in sedimentary rocks like sandstone, shale, etc.
- Metamorphic Rocks: The word ‘metamorphic’ means ‘change of form’. These rocks form under the action of pressure, volume and temperature (PVT) changes. Metamorphism occurs when rocks are forced down to lower levels by tectonic processes or when molten magma rising through the crust comes in contact with the crustal rocks or the underlying rocks are subjected to great amounts of pressure by overlying rocks.
Q 51 – What are metamorphic rocks? Describe the types of metamorphic rock and how are they formed?
Ans. The word metamorphic means ‘change of form’. These rocks form under the action of pressure, volume and temperature (PVT) changes. Metamorphism takes place when rocks are forced down to lower levels by tectonic processes or when molten magma rising through the crust comes in contact with the crustal rocks or the underlying rocks are subjected to great amounts of pressure by overlying rocks. Metamorphism is a process by which already consolidated rocks undergo recrystallisation and reorganisation of materials within original rocks.
Mechanical disruption and reorganisation of the original minerals within rocks because of breaking and crushing without any appreciable chemical changes is called dynamic metamorphism. The materials of rocks chemically alter and recrystallise due to thermal metamorphism.
There are two types of thermal metamorphism:
1. Contact metamorphism: In contact metamorphism the rocks come in contact with hot intruding magma and lava and the rock materials recrystallise under high temperatures. Quite often new materials form out of magma or lava are added to the rocks.
2. Regional metamorphism: In regional metamorphism, rocks undergo recrystallisation due to deformation caused by tectonic shearing together with high temperature or pressure or both.
During metamorphism in some rocks grains or minerals get arranged in layers or lines. Such an arrangement of minerals or grains in metamorphic rocks is called foliation or lineation. Sometimes minerals or materials of different groups are arranged into alternating thin to thick layers appearing in light and dark shades. Such a structure in metamorphic rocks is called banding and rocks displaying banding are called banded rocks. Types of metamorphic rocks depend upon original rocks that were subjected to metamorphism. Metamorphic rocks are classified into two major groups foliated rocks and non-foliated rocks. Gneissoid, granite, syenite, slate, schist, marble, quartzite etc. are some examples of metamorphic rocks.
Q 52 – What does Pyroxene consists of? What percent of the earth does it occupy? What kind of colour it has?
Ans. Pyroxene consists of calcium, aluminum, magnesium, iron and silica. Pyroxene forms 10 per cent of the earth’s crust. It is in green or black colour.
Q 53 – What does Amphibole consists of? What percent of the earth does it occupy? What kind of colour it has? Where is it used?
Ans. Aluminium, calcium, silica, iron, magnesium are the major elements of amphiboles. They form 7 per cent of the earth’s crust. It is in green or black colour and is used in asbestos industry.
Q 54 – What are the important elements of the crust of the earth?
Ans. About 98 percent of the total crust of the earth is composed of eight elements like oxygen, silicon, aluminium, iron, calcium, sodium, potassium and magnesium, and the rest is constituted by titanium, hydrogen, phosphorous, manganese, sulphur, carbon, nickel and other elements.
Q 55 – What do you mean by cleavage?
Ans. The tendency to break in given directions producing relatively plane surfaces is called cleavage.
Q 55 –What do you mean by fracture?
Ans. Internal molecular arrangement is sc complex that there are no planes o molecules; the crystal will break in an irregular manner, not along planes of cleavage
Q 56 – What does Feldspar consists of? What percent of the earth does it occupy? What kind of colour it has? Where is it used?
Ans. Silicon and oxygen are common elements in all types of feldspar and sodium, potassium, calcium, aluminium etc. are found in specific feldspar variety. Half of the earth’s crust is composed of feldspar. It has light cream to salmon pink colour. It is used in ceramics and glass making.
Q 57 – What is petrology?
Ans. It is science of rocks. A petrologist studies rocks in all their aspects viz., mineral composition, texture, structure, origin, occurrence, alteration and relationship with other rocks.
Q 58 – Give some examples of igneous rocks.
Ans. Granite, gabbro, pegmatite, basalt, volcanic breccia and tuff are some of the examples of igneous rocks.
Q 59 – What is rock cycle?
Ans. Rock cycle is a continuous process through which old rocks are transformed into new ones.
Q 60 – What is Quartz? Give some of its features.
Ans. It is one of the most important components of sand and granite. It consists of silica. It is a hard mineral virtually insoluble in water. It is white or colourless and used in radio and radar. It is one of the most important components of granite.
Q 61 – What is the form of inner and outer form of the earth?
Ans. The interior most part of the earth is in liquid form but its uppermost layer is in the form of solid.
Q 62 – What is the root source of all types of rocks?
Ans. Magma which is found in the interior of the earth is the root source of all minerals.
Q 63 – Give one example of solid, liquid and gaseous form of minerals.
Ans. Solid form of minerals is coal, liquid form is petroleum and diesel and gaseous form is natural gas
Q 64 – What does mica consists of? What per cent, of the earth crust consists of mica? In which type of rocks is it found? Where is it used?
Ans. It comprises of potassium, aluminium, magnesium, iron, silica etc. It forms 4 per cent of the earth’s crust. It is commonly found in igneous and metamorphic rocks. It is used in electrical instruments.
Q 65 – What are non-metallic minerals? Give examples.
Ans. These minerals do not contain metal content. Sulphur, phosphates and nitrates are examples of non-metallic minerals. Cement is a mixture of non- metallic minerals.
Q 66 – What does Olivine consists of? In which type of rocks is it found?
Ans. Magnesium, iron and silica are major elements of olivine. It is used in jewellery. It is usually a greenish crystal, often found in basaltic rocks
Q 67 – What are the root sources of igneous rocks?
Ans. Magma is the root source of igneous rocks. The igneous rocks are formed when magma cools and solidifies. When magma in its upward movement cools and turns into solid form it is called igneous rock. The process of cooling and solidification can happen in the earth’s crust or on the surface of the earth.
Q 68 – How does systematic formation of minerals take place?
Ans. The basic source of all minerals is the hot magma in the interior of the earth. When magma cools, crystals of minerals appear and a systematic series of minerals are formed in sequence to solidify so as to form rocks.
Q 69 – What kind of qualities do minerals have?
Ans. A mineral is a naturally occurring organic and inorganic substance having an orderly atomic structure and a definite chemical composition and physical properties for example sulphur, copper, silver, and gold, etc.
Q 70 – Name the minerals which are single elements?
Ans. Sulphur, copper, silver, gold, graphite are single elements.
Q 71 – Name the hardest and softest mineral?
Ans. Diamond is the hardest and Talc is the softest mineral
Q 72 – Name the mineral which is used in Asbestos industry?
Ans. Amphiboles is used in Asbestos industry.
Q 73 – What are metallic minerals? Explain their classification with examples.
Ans. These minerals contain metal content and can be sub-divided into three types:
- Precious metals: Gold, silver, platinum, etc.
- Ferrous metals: Iron, nickel, chromite, maganese.
- Non-ferrous metals: Copper, lead, zinc, tin, etc.
Q 74 – Explain the features of sedimentary rocks.
Ans. The word ‘sedimentary’ is derived from the Latin word sedimentum, which means settling. All types of rocks of the earth’s surface are exposed to denudational agents, and are broken up into various sizes of fragments. Such fragments are transported by different exogenous agencies and deposited. These deposits through compaction turn into rocks. This process is called lithification. In many sedimentary rocks, the layers of deposits retain their characteristics even after lithification. Hence, we see a number of layers of varying thickness in sedimentary rocks like sandstone, shale, etc.
Differentiate between:.
- Minerals and rocks
- Sedimentary and igneous rocks
- Igneous and metamorphic rocks
- Extrusive Igneous and intrusive igneous.
(i) Minerals and rocks
| S.no | Minerals | Rocks |
| 1. | Naturally occurring substances with the definite chemical and physical composition. | Solid or the soften portion of the earth crust. |
| 2. | May be composed of two or more elements. | Are of three types and comprises of various metals. |
| 3. | More than 2, 000 minerals exist. | Classified as Igneous, sedimentary and Metamorphic rocks. |
(ii) Sedimentary and igneous rocks
| S.no | Sedimentary rocks | Igneous rocks |
| 1. | Made up of sediments. | Made up of solidified lava. |
| 2. | Loose sediments get sedimented into rocks. | Liquid lava gets solidified by gradual cooling. |
| 3. | Form in layers. | They are compact. |
| 4. | Contains fossils. | Do not have fossils. |
| 5. | Are organic and inorganic in nature. | They are extrusive or intrusive. |
| 6. | Permeable and allow water to seep. | In permeable and do not allow water to seep. |
| 7. | They are known as secondary rocks, these are of two types: Intrusive- granite, Diorite; Extrusive-basalt. | They are known as primary rocks e.g. organic rock-coal, limestone Inorganic- sandstone, shale. |
(iii) Igneous and metamorphic rocks
| S.no | Igneous rocks | Metamorphie rocks |
| 1. | Magma cools and solidifies. | Igneous and sedimentary rocks and are changed into metamorphie rock due to heat and temperature. |
| 2. | Igneous rocks are normally crystalline and are of two types- Intrusive and Extrusive. | Metamorphism can be of two types contact metamorphism and regional metamorphism. |
| 3. | Hard, Impermeable in nature. | They are also hard but have formed due to change in igneous and sedimentary rocks for e.g. Limestone changes into marble, sandstone into quartzite and coal into graphite. |
| 4. | In igneous rocks no bands are seen. | In metamorphie rocks banding is a normal. |
| 5. | In the intensive igneous rocks the cooling and solidification decides the size of the particles. | The arrangement of the minerals of granules is called lineation. |
(iv) Extrusive Igneous and intrusive igneous.
| S.no | Extrusive Igneous | Intrusive Igneous |
| 1. | Lava cools rapidly on the surface of earth. | Cooling and solidification occurs inside the earth surface and is a slow process. |
| 2. | Minerals crystals of extrusive igneous rocks change their structure and can became very small in size e.g. Basalt. | They are the coarse granule structure e.g. Granite Doloride. |
Q 75 – Explain any six physical characteristics?
Ans. Brief information about some important minerals in terms of their nature and physical characteristics is given below :
- External crystal form: Determined by internal arrangement of the molecules- cubes octahedrons, hexagonal prism, etc.
- Fracture: Internal molecular arrangement so complex there are two planes of molecules; the crystal will break in an irregular manner, not along planes of cleavage.
- Lustre: Appearance of a material without regard to color; each mineral has a distinctive lustre like metallic, silky, glossy, etc.
- Streak: Colour of the ground powder of any mineral. It may be of the same colour as the mineral or may differ malachite is green and gives green streak.
- Structure: Particular arrangement of the individual crystal; fine, medium or coarse grained; fibrous separable, divergent and radiating.
- Specific gravity: The ratio between the weight of a given object and the weight of an equal volume of water; object weighted in air and then weighed in water and divide weight in air by the difference of the two weights.
Q 76 – Explain some important minerals and their characteristics.
Ans. Some major minerals and their characteristics
- Feldspar: Silicon and oxygen are common elements in all types of feldspar and sodium, potassium, calcium, aluminium etc. are found in specific feldspar variety.
- Question uartz: It is one of the most important components of sand and granite. It consists of silica. It is a hard mineral virtually insoluble in water.
- Pyroxene: Pyroxene consists of cak ium, aluminum, magnesium, iron and silica. Pyroxene forms 10 percent of the earth’s crust.
- Amphibole: Aluminium, calcium, silica, iron, magnesium are the major elements of amphiboles. They form 7 per cent of the earth’s crust.
- Mica: It comprises of potassium, aluminium, magnesium, iron, silica etc. It forms 4 per cent of the earth’s crust.
- Olivine: Magnesium, iron and silica are major elements of olivine. It is used in jewellery. It is usually a greenish crystal, often found in basaltic rocks.
Q 77 – Rocks do not remain in their original form for long but may undergo transformation. Explain.
Ans. Rocks do not remain in their original form for long but may undergo transformation. Rock cycle is a continuous process through which old rocks are transformed into new ones. Igneous rocks are primary rocks and other rocks form from these primary rocks. Igneous rocks can be changed into metamorphic rocks. The fragments derived out of igneous and metamorphic rocks form into sedimentary rocks. Sedimentary rocks themselves can turn into fragments and the fragments can be a source for formation of sedimentary rocks. The crustal rocks (igneous, metamorphic and sedimentary) once formed may be carried down into the mantle through subduction process and the same melt down due to increase in temperature in the interior and turn into molten magma, the original source for igneous rocks.
Q 78 –Igneous rocks act as a source of all other types of rocks. Justify.
Ans. Yes, it is right to say that igneous rocks act as a source of all other rocks. Therefore these are also called primary rocks.
Igneous rocks are primary rocks and other rocks i.e. sedimentary and metamorphic formed from these primary rocks. Igneous rocks can be changed into metamorphic rocks. The fragments derived out of igneous and metamorphic rocks form into sedimentary rocks. Sedimentary rocks themselves can turn into fragments and the fragments can be a source for formation of sedimentary rocks. The crustal rocks (igneous, metamorphic and sedimentary) once formed may be carried down into the mantle (interior of the earth) through subduction process (parts or whole of crustal plates going down under another plate in zones of plate convergence) and the same melt down due to increase in temperature in the interior and turn into molten magma, the original source for igneous rocks.
Q 79 – Metallic minerals are more useful as compared to non metallic minerals. Do you agree? Justify your answer
Ans. No, I do not agree. Minerals both metallic and non metallic have their own importance.
1. Metallic minerals: These minerals contain metal content and can be sub-divided into three types:
- Precious metals: Gold, Sivler, Platinum, etc
- Ferrous metals: Iron, Nickel, Chromite, Maganese
- Non-ferrous metals: Copper, Lead, Zinc, Tin etc.
2. Non metallic minerals: These minerals do not have a metal content. Sulphur, phosphates and nitrates are some of the examples. Cement is a mixture of non metallic mineral. These minerals have their own utility. We can’t manage without these minerals.
Q 80 –Classify the sedimentary rocks on the basis of mode of formation.
Ans. Depending upon the mode of formation, sedimentary rocks are classified into three major groups:
- Mechanically formed: Some of its examples are sandstone, conglomerate, limestone, shale, loess, etc.
- Organically formed: Some of its examples are geyserite, chalk, limestone, coal, etc.
- Chemically formed: Some of its examples are chert, limestone, halite, potash, etc.