- Minerals and rocks
NCERT Questions:
Multiple choice questions:
(i) 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
Ans. c) Silica and aluminium
(ii) Which one of the following is the salient feature of metamorphic rocks?
a) Changeable
b) Quiet
c) Crystalline
d) Foliation
Ans. a) Changeable
(iii) Which one of the following is not a single element mineral?
a) Gold
b) Silver
c) Mica
d) Graphite
Ans. c) Mica
(iv) Which one of the following is the hardest mineral?
a) Topaz
b) Diamond
c) Quartz
d) Feldspar
Ans. b) Diamond
(v) Which one of the following is not a sedimentary rock?
a) Tillite
b) Borax
c) Breccia
d) Marble
Ans. d) Marble
- Answer the following questions in about 30 words:
(i) What do you mean by rocks? Name the three major classes of rocks.
Ans.
a) The Earth’s crust is composed of rocks.
b) The rock is an aggregate of one or more minerals. It may be hard or soft and of varied colours.
c) For example, granite is hard soap-stone is soft, gabbro is black, and quartzite can be milky white.
d) Rocks do not have definite composition of mineral constituents.
e) Feldspar and quartz are the most common minerals found in rocks.
i) The three major classes of rocks on the basis of their mode of formation are:
i) Igneous rocks – Solidified from magma and lava.
ii) Sedimentary rocks – The result of deposition of fragments of rocks by exogenous processes.
iii) Metamorphic rocks – Formed out of existing rocks undergoing recrystallization.
(ii) What is an igneous rock? Describe the method of formation and characteristics of igneous rock.
Ans.
a) As igneous rocks are formed out of magma and lava from the interior of the Earth, they are known as primary rocks.
b) The igneous rocks (Ignis in Latin means ‘fire’) are formed when magma cools and solidifies.
c) The process of cooling and solidification can go in the Earth’s crust or on the surface of the Earth (Intrusive or extrusive).
d) Igneous rocks are classified based on texture. Texture depends upon size and arrangement of grains or other physical conditions of the materials.
e) 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 condition of cooling would result in intermediate size of grains making up igneous rocks.
f) Granite, gabbro, pegmatite, basalt, volcanic breccia and tuff are some of the examples of igneous rocks.
(iii) What is meant by sedimentary rock? Describe the mode of formation of sedimentary rock.
Ans.
a) The word sedimentary is derived from the Latin word sedimentum, which means settling.
b) Rocks (igneous, sedimentary and metamorphic) of the Earth’s crust surface are exposed to denudation agents and are broken up into various sizes of fragments.
c) Such fragments are transported by different exogenous agencies and deposited.
d) These deposits, through compaction turn into rocks. This process is called Lithification.
e) In many sedimentary rocks, the layers of deposits retain their characteristics. Even after Lithification.
f) Hence we see a number of layers of varying thickness in sedimentary rocks like sandstone, shale etc.
g) Depending upon the mode of formation, sedimentary rocks are classified into three major groups.
i) Mechanically formed – sandstone, conglomerate, limestone, shale, loess etc.
ii) Originally formed – geyserite, chalk, limestone, coal etc.
iii) Chemically formed – chert, limestone, halite, potash etc.
(iv) What relationship is explained by rock cycle between the major types of rock?
Ans.
a) Rocks do not remain in their original form for long, but may undergo transformation.
b) 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.
c) Igneous rocks can be changed into metamorphic rocks.
d) The fragments derived out of igneous and metamorphic rocks form into sedimentary rocks.
e) Sedimentary rocks themselves can turn into fragments, and the fragments can be a source of formation of sedimentary rocks.
f) 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 zone 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.
Answer the following questions in about 150 words:
(i) Define the term mineral and name the major classes of minerals with their physical characteristics.
Ans.
a) A mineral is a naturally occurring organic and inorganic substance having an orderly atomic structure, and definite chemical composition and physical properties.
b) A mineral is composed of two or more elements, but sometimes single element minerals like sulphur, copper, silver, gold, graphite etc. are found.
c) Though the number of elements making up the lithosphere is limited, they are combined in many different ways to make up many varieties of minerals.
d) There are at least 2000 minerals that have been named and identified in the Earth crust. But almost all the commonly occurring once is related to six major mineral groups that are known as major rock forming minerals.
e) About 98% of the total crust of the earth is composed of 8 elements like oxygen, silicon, aluminium, iron, calcium, sodium, potassium and magnesium and the rest is constituted by titanium, hydrogen, phosphorus, manganese, sulphur, carbon, nickel and other elements.
f) The elements In the Earth’s crust are rarely found exclusively, but are usually combined with other elements to make various substances. These substances are recognised as minerals.
Physical Characteristics
a) External crystal form – determined by internal arrangement of the molecules cubes, octahedrons, hexagonal prisms, etc.
b) Cleavage – tendency to break in different directions, producing relatively plane surfaces, result of internal arrangement of the molecules may leave in one or more directions and at any angle to each other.
c) Fracture – internal molecular arrangements so complex that there are no planes of molecules. The crystal will break in an irregular manner, not along planes or cleavage.
d) Lustre – appearance of a material without regard to colour. Each mineral has a distinctive lustre like metallic, silky, glossy etc.
e) Colour – some minerals have characteristic colour determined by their molecular structure. Malachite, azurite, chalcopyrite etc., and some minerals are coloured by impurities. For example because of impurities, quarts may be white, green, red, yellow, etc.
f) Streak – colour of the ground powder of any mineral. It may be of the same colour as a mineral or may differ malachite is green and gives green streak, fluoride is purple or green but gives a white streak.
g) Transparency – transparent light rays pass through so that objects can be seen clearly. Translucent light rays pass through but will get diffused so that objects cannot be seen. Opaque light will not pass at all.
h) Structure – particular arrangement of the individual crystals; fine, medium or coarse grained, fibrous, separable, divergent, radiating.
i) Hardness – relative resistance being scratched. Ten minerals are selected to measure the degree of hardness from 1 to 10:
| Moho’s hardness scale: | |
| 10 | Diamond (hardest) |
| 9 | Corundum |
| 8 | Topaz |
| 7 | Quartz |
| 6 | Feldspar |
| 5 | Appetite |
| 4 | Fluoride |
| 3 | Calcite |
| 2 | Gypsum |
| 1 | Talc (softest) |
j) Specific gravity – the ratio between the weight of a given object and the weight of an equal volume of water; object weight in air and then weight in water and divide weight in air by the difference of the two weights.
(ii) Describe the nature and mode of origin of the chief types of rock at the Earth’s crust. How will you distinguish them?
Ans. A rock is an aggregate of one or more minerals. There are three different types of rocks:
i) Igneous rocks (primary rocks)
ii) Sedimentary rocks (secondary rocks)
iii) Metamorphic rocks (secondary rocks)
a) Rocks do not remain in their original form for long, but may undergo transformation.
b) 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.
c) Igneous rocks can change into metamorphic rocks.
d) The fragments derived out of igneous and metamorphic rocks form into sedimentary rocks.
e) Sedimentary rocks themselves can turn into fragments, and the fragments can be a source of formation of sedimentary rocks.
f) 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 zone 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.
(iii) What are the metamorphic rocks? Describe the types of metamorphic rock and how are they formed?
Ans.
a) The word metamorphic means change of form. These rocks fall under the action of pressure, volume and temperature (PVT) changes.
b) 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 crystal rocks or the underlying rocks are subjected to great amounts of pressure by overlying rocks.
c) Metamorphism is a process by which already consolidated rocks undergo recrystallization and reorganization of materials within original rocks.
d) Mechanical disruption and reorganization of the original minerals within rocks due to breaking and crushing without any appreciable chemical changes is called dynamic metamorphism.
e) The materials of rocks chemically altered and recrystallize due to thermal metamorphism.
f) There are two types of thermal metamorphism, contact metamorphism and regional metamorphism. In contact metamorphism the rocks come in contact with hot, intruding magma, and the raw material recrystallized under high temperatures.
g) Quite often new materials form out of magma and lava are added to the rocks.
h) In regional metamorphism rocks undergo recrystallization due to deformation caused by tectonic shearing together with high temperature or pressure or both.
i) In the process of 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.
j) Sometimes minerals or materials of different groups are arranged into alternative thin to thick layers appearing in light and dark shades. Such a structure in metamorphic rocks is called banding, and rocks displaying bending are called bending rocks.
k) Types of metamorphic rocks depend upon original rocks that were subjected to metamorphism.
l) Metamorphic rocks are classified into two major groups, foliated rocks and nonfoliated rocks.
m) Gneissoid, granite, syenite, slate, schist, marble, quartzite etc. are some examples of metamorphic rocks.
Question Bank:
Multiple choice questions:
- A non-metallic mineral in the following is:
a) Silver
b) Copper
c) Zinc
d) Coal
Ans. d) Coal
Coal is used as a fossil fuel and is a non-metallic mineral with dull non-reflective properties and it cannot be moulded in any form.
- Formation of metamorphic rocks includes the process of:
a) Recrystallization
b) Solidification
c) Lithification
d) Carbonation
Ans. a) Recrystallization
When consolidation of rocks undergoes recrystallization and reorganization of materials within it, metamorphic rocks are formed.
- The principle ore of aluminium is:
a) Magnetite
b) Hematite
c) Chlorite
d) Bauxite
Ans. d) Bauxite
The principle ore of aluminium is bauxite, radish clay like ore rich in alumina. The ore is first converted into pure alumina. Aluminium is then extracted by electrolysis at a reduction plant or smelter.
- World’s most commonly used metal in steel is:
a) Aluminium
b) Iron
c) Calcium
d) Sodium
Ans. b) Iron
Iron is the world’s most commonly used metal in steel, of which iron ore is the key ingredient and represents almost 95% of all metal used per year.
- The number of mineral identified on earth’s crust is:
a) 1997
b) 1998
c) 1999
d) 2000
Ans. d) 2000
2000 minerals are identified on the earth’s crust that are related to six major mineral groups known as major rock forming minerals.
- A mineral that is colourless and used in radio and radar is:
a) Granite
b) Quartz
c) Sandstone
d) Marble
Ans. a) Granite
Granite is 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 the most important components of granite.
- 11% of the earth’s crust is formed by:
a) Amphibole
b) Pyroxene
c) Mica
d) Olivine
Ans. b) Pyroxene
Pyroxene forms 11% of the Earth’s crust. Pyroxene consists of calcium, aluminum, magnesium, iron and silica. It is commonly found in meteorites. It is in green or black in colour. The most abundant minerals in Earth’s continental crust are feldspars, which make up about 41% of the crust by weight, followed by quartz at 12% and pyroxenes at 11%.
- The rocks formed by the deposits of animal shell and skeletons are:
a) Sandstone
b) Limestone
c) Quartz
d) Basalt
Ans. b) Limestone
Limestone rocks are sedimentary rocks that are made from the mineral calcite which came from the beds of evaporated seas lakes and from sea animal shells. This rock is used in concrete and is an excellent building stone for humid regions.
- Igneous rocks are classified on the basis of:
a) Density
b) Colour
c) Strength
d) Texture
Ans. d) Texture
Igneous rocks are classified on the basis of texture. Texture depends upon size and arrangement of grains or other physical conditions of the materials.
- The two main constituents of granite are:
a) Iron and nickel
b) Iron and silver
c) Silica and aluminium
d) Iron oxide and potassium
Ans. d) Iron oxide and potassium
Granite is a common and widely occurring type of intrusive, felsic, igneous rock with a constituent of Iron oxide and potassium. It has a medium to coarse texture, occasionally with some individual crystal larger than the ground mass forming a rock known as porphyry. Granite can be pink to dark grey or even black depending on their chemistry and mineralogy.
- The most abundant rocks found on the earth crust are:
a) Igneous rocks
b) Sedimentary rocks
c) Metamorphic rocks
d) Granite rock
Ans. a) Igneous rock
Igneous rocks are formed from the solidification of lava or magma which is hot (600˚C to 1300˚C) molten or partially molten rock material. The earth is composed predominantly of a large mass of igneous rock with a very thin covering of sedimentary rock.
- When the sediments turn into rocks through compaction, it is called:
a) Solidification
b) Lithification
c) Metamorphism
d) Recrystallization
Ans. b) Lithification
Rocks of the earth’s surface are exposed to denudational agents, and are broken up into various sizes or fragments. Such fragments are transported by different exogenous agencies and deposited. These deposits through compaction turn into rocks. This process is called Lithification.
- The metamorphic rock is:
a) Sandstone
b) Shale
c) Chalk
d) Marble
Ans. d) Marble
Metamorphic rocks are classified into two major groups- foliated and non-foliated rocks. Gneissoid, syenite, slate, schist, marble, quartzite etc. are some examples of metamorphic rocks, which is a metamorphosed form of limestone.
- The word metamorphic means:
a) Settling
b) Applying pressure
c) Breaking up into fragments
d) Change of form
Ans. d) Change of form
The word metamorphic means ‘change of form’. These rocks form under the action of pressure, volume, and temperature (PVT) changes.
- The minerals that do not contain metal content are known as:
a) Precious minerals
b) Ferrous minerals
c) Non-metallic minerals
d) Non-ferrous minerals
Ans. c) Non-metallic minerals
The minerals that do not contain metal content are known as non-metallic minerals. Sulphur, phosphate and nitrates are examples of non-metallic minerals.
- The basic source of mineral is:
a) Rocks
b) Hot magma
c) Alluvial deposits
d) Sedimentary rocks
Ans. b) Hot magma
When magma cools, crystals of minerals appear and they solidify to form rocks.
- The hardest mineral is:
a) Topaz
b) Quartz
c) Diamond
d) Feldspar
Ans. c) Diamond
Diamond is the hardest known material on the Moho’s scale of mineral hardness, where hardness is defined as resistance to scratching and is graded between 1 (softest) and 10 (hardest). Diamond has a hardness of 10 (hardest) on this scale and is four times harder than corundum – 9 Moho’s scale. Diamond has the highest hardness and thermal conductivity of any bulk material. Those properties determine the major industrial application of diamond in cutting and polishing.
- The parent material of soils is derived from:
a) Fossil fuels
b) Molten magma
c) Sedimentary rocks
d) Marine deposits
Ans. c) Sedimentary rocks
The parent rock refers to the original rock from which something else was formed. It is mainly used in the context of soil formation where the parent rock will have a large influence on the nature of the resulting soil. The term is also used in the context of metamorphic rocks where again the parent rock refers to the original rock where metamorphism takes place. Parent rock can be sedimentary, igneous or metamorphic.
- Sedimentary rocks are finally and ultimately derived from the:
a) Weathering of igneous
b) Metamorphic rocks
c) Marine deposits
d) Action of earth movements
Ans. a) Weathering of igneous rocks
The sediments are result of weathering which breaks up pre-existing igneous rocks. It is formed by deposition and consolidation of mineral and organic material and from precipitation of minerals from solution. A sedimentary rock is an accumulation of fragments of pre-existing rocks. The processes that form sedimentary rock occur at the surface of the earth and within water. There are three types of sedimentary rocks; clastic, chemical and biochemical rocks.
- Iron is a:
a) Ferrous metal
b) Non-ferrous metal
c) Precious rock
d) Rock
Ans. Ferrous metal
Iron is a metallic mineral. Alloying iron with appropriate small amounts of other metals and carbon produces steel, which can be 1,000 times harder than pure iron.
- Half of the earth’s crust is composed of:
a) Granite
b) Feldspar
c) Iron
d) Silica
Ans. b) Feldspar
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.
- The mineral which is used in radio and radar is:
a) Feldspar
b) Quartz
c) Mica
d) Pyroxene
Ans. b) Quartz
The mineral which is used in radio and radar is quartz. It is white or colour less.
- The term igneous is derived from Latin word:
a) Soil
b) Water
c) Fire
d) Mountain
Ans. c) Fire
The term igneous is derived from Latin word fire. The igneous rocks are formed when magma cools and solidifies.
- One of the major elements of olivine is:
a) Copper
b) Silver
c) Magnesium
d) Carbon
Ans. c) Magnesium
Magnesium, iron and silica are major elements of olivine. It is used in jewellery; it is usually a greenish crystal, often found in basalt.
- One of the elements of amphibole is:
a) Bauxite
b) Potassium
c) Aluminium
d) Calcium
Ans. a) Bauxite
Bauxite, calcium, silica, iron magnesium is the major elements of amphiboles. They form 7% of earth’s crust.
- An arrangement of minerals in metamorphic rock is called:
a) Foliation
b) Re-crystallization
c) Lithification
d) Metamorphism
Ans. a) Foliation
In the process of metamorphism, some rocks, grains or minerals get arranged in layers or lines. Such an arrangement of minerals or grains in metamorphic rocks is called foliation.
- Petrology is the science of:
a) Water
b) Soil
c) Forest
d) Rocks
Ans. d) Rocks
Petrology is the science of rocks. A petrologist studies rocks in all their aspects viz., mineral composition, texture, structure, origin, occurrence, alteration and relationship with other rocks.
- Limestone’ shale’ sandstone, loess etc. are the examples of:
a) Metamorphic rocks
b) Sedimentary rocks
c) Igneous rocks
d) Non-metallic rocks
Ans. b) Sedimentary rocks
Lime stone’ shale’ sandstone, loess etc. are the examples of sedimentary rocks. The word sedimentary is derived from the Latin word ‘sedimentum’, which means settling.
- Mica is commonly found in:
a) Igneous and metamorphic rocks
b) Sedimentary and igneous rocks
c) Metamorphic and sedimentary rocks
d) Sedimentary rocks
Ans. a) Igneous and metamorphic rocks
Mica is only found in igneous and metamorphic rocks. It is used in electrical instruments.
- Which of the following are the major constituents of granite?
a) Iron and nickel
b) Iron and silver
c) Silica and aluminium
d) Iron oxide and potassium
Ans. c) Silica and alumina
The chemical composition of granite is typically 70-77% silica; 11-13% alumina, 3-5% potassium oxide, 3-5% soda, 1% lime, 2-3% total iron and less than 1% magnesia and titania.
- Igneous rocks are:
a) Primary rocks
b) Secondary rocks
c) Tertiary rocks
d) Soft rocks
Ans. a) Primary rocks
As igneous form out of magma and lava from the interior of the earth, they are known as primary rocks.
- Gypsum, saltpetre, pyrite and haematite all can be found in:
a) Sedimentary rocks
b) Igneous rocks
c) Metamorphic rocks
d) Metallic minerals
Ans. a) Sedimentary rocks
Gypsum, saltpetre, pyrite and haematite all can be found in sedimentary rocks.
- The number of economic minerals associated with sedimentary rocks is:
a) More than associated with igneous rocks
b) Less than that associated with igneous rocks
c) Same as that of igneous rocks
d) Unknown
Ans. b) Less than that associated with igneous rocks
The number of economic minerals associated with sedimentary rocks is less than that associated with igneous rocks. The basic source of all mineral 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. Mineral such as coal, petroleum and natural gas are organic substances found in solid, liquid and gaseous forms respectively.
- In which state does the formation of metamorphic rocks takes place?
a) Always in liquid state
b) Always in solid state
c) Sometimes in liquid and sometimes in solid
d) Always by chemical recombination process
Ans. Always in solid state
Due to excessive pressure of high temperature, the properties of rocks get transformed. During this process, the rock remains mostly in solid state, but gradually recrystallizes to a new texture or mineral composition. The protolith (metamorphism) may be an igneous, sedimentary or existing metamorphic rock.
- Magma that reaches the surface of the earth and then solidifies is known as:
a) Granite
b) Lava
c) Quartz
d) Silicates
Ans. b) Lava
Lava is the molten rock expelled by a volcano during an eruption and the resulting rock after solidification and cooling is igneous rock.
- _____ is the types of igneous rocks:
a) Granite and basalt
b) Quartz and marble
c) Sandstone and limestone
d) Shale and loess
Ans. a) Granite and basalt
Granite, basalt, gabbro, pegmatite, volcanic breccia and tuff are some types of igneous rocks.
- What forms 11% of the earth’s crust?
a) Amphibole
b) Pyroxene
c) Mica
d) Olivine
Ans. b) Pyroxene
Pyroxene consists of calcium, aluminium, magnesium, iron and silica. Pyroxene forms 10% of the earth’s crust.
- The salient feature of metamorphic rock is that it is:
a) Changeable
b) Crystalline
c) Quite
d) Foliation
Ans. b) Crystalline
The salient feature of metamorphic rock is that it is crystalline.
Short answer type questions:
- What do you mean by rocks? Name the different types of rocks?
Ans. A rock is an aggregate of one or more minerals. There are three different types of rocks:
a) Igneous rocks (primary rocks)
b) Sedimentary rocks (secondary rocks)
c) Metamorphic rocks (secondary rocks)
- What is Lithification?
Ans. The process of compaction of sediments through which they turn into rocks is called Lithification.
- What is a mineral?
Ans. Mineral is an organic element or compound with definite chemical composition, atomic and chemical structure and definite set of physical properties.
- Name some igneous rocks?
Ans. Granite, basalt, dolerite, dolomite are some of the example of igneous rocks.
- What is sedimentary rock?
Ans. The rock which is formed by the accumulation of sediments is called a sedimentary rock. Limestone, sandstone, chalk, gypsum are some of the examples of sedimentary rocks.
- Highlight four important characteristics of feldspar mineral.
Ans. Characteristics of feldspar:
a) It is light pink to salmon in colour.
b) About half of the earth’s crust comprises feldspar.
c) Silicon and oxygen are common elements found in all types of feldspar while sodium, potassium, calcium and aluminium are found in a specific variety of feldspar.
- What do you mean by petrology? What is the role of petrologist?
Ans. Petrology is the science of studying rocks. A petrologist studies different aspects of rocks like mineral composition, texture, structure, origin, alteration of rocks and their relationship with the other types of rocks.
- What are metallic minerals? Classify.
Ans. Minerals having a good amount of metallic content are known as metallic minerals. They can be classified as:
a) Precious metals: gold, silver, platinum
b) Ferrous metals: iron and other metals mixed to form steel
c) Non-ferrous metals: copper, lead, zinc, tin.
- Identify the following types of rocks:
a) Basalt
b) Limestone
c) Pegmatite
d) Granite
Ans. The following rocks are:
a) Basalt: igneous rock
b) Limestone: sedimentary rock
c) Pegmatite: igneous rock
d) Granite : igneous rock
- How the sedimentary rocks are formed?
Ans.
a) Loose materials are deposited in the form of layers.
b) Stratification takes place as fine sediments like clay and silt deposited in layers settle down in due course.
c) These loose materials get converted into hard and compact rocks known as sedimentary rocks.
- Why is the igneous rocks called a primary rock?
Ans. Igneous rocks are the first rocks found on this earth. They are being formed in regions of volcanic activity. Out of all the rocks, they are the first to be formed and from them, others are formed. Hence, they are called primary rocks. Granite, gabbro, pegmatite, basalt, volcanic breccia and tuff are some of the examples of igneous rocks.
- Why are fossils preserved in sedimentary rocks and not in igneous rocks?
Ans. Sedimentary rocks are formed by the deposition of sediments carried away by Exogenic agents such as water, wind, air etc. they are deposited in distinct strata or layers. Fossils in the form of layers of plants, insects or animals and pieces of bones are deposited in layers of the sedimentary rocks. On the other hand, igneous rocks are formed by the solidification of magma. They have no layers.
- What is metamorphism?
Ans. Metamorphism is a term covering all the processes by which rocks are altered in their mineralogy, texture and internal structure owing to Exogenic factors such as heat, pressure and chemical changes. Due to metamorphism, igneous and sedimentary rocks are totally changed in their physical and chemical composition. Example: slate, marble etc.
- What are the main characteristics if igneous rocks:
Ans. The main characteristics of igneous rocks are:
a) These rocks are found in huge quantity
b) They are thermal in origin
c) These rocks are extremely hard and resistant.
d) They are crystalline.
e) They are of volcanic origin.
f) They are not in layers.
- How is lime stone formed?
Ans. Limestone is mainly composed of shells or skeletons of animals or plants and is formed of carbonates of lime. Deposits of carbonate of lime sometimes produced, when water containing a large proportion of that mineral evaporates and leaves carbonate of lime behind. The lime shells of such an organism; living in moderately deep and clear water of sea or lake are cemented into limestone.
- Describe in detail the two main processes of metamorphism and their impact on rocks.
Ans. The two main processes of metamorphism are:
a) Content metamorphism: It is a process of change inside the rocks affected by heat in the proximity of magma intrusion in the rocks. The heat is produced by magma and water vapour, which produce chemical replacement, re-crystallization and mechanical changes inside the rocks and makes it a great source of valuable minerals.
b) Regional metamorphism: It is a process in which rocks are changed mainly by high pressure. The rocks undergo re-crystallisation by the deformation of crystals. This leads to an increase in the pressure and temperature of the region.
- Name the minerals found in metamorphic rocks.
Ans. The common minerals in metamorphic rocks are the same as the rock forming silicates found in igneous rocks with the addition of a few high temperature, high pressure forms some different minerals that are common in metamorphic rocks are kainite, granite, sillimanite, andalusite and corundum.