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Properties of Rocks.pptx

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The document discusses the properties and classification of three main types of rocks: igneous, sedimentary, and metamorphic rocks. Igneous rocks form from cooling magma, sedimentary rocks form through accumulation and compaction of sediments, and metamorphic rocks form from changes to pre-existing rocks through heat, pressure, and chemically-active fluids. The document describes the formation processes, typical mineral compositions, and textural characteristics of each rock type. It also discusses classification schemes for igneous and metamorphic rocks based on silica content and foliation, respectively.

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Properties of Rocks Dr. K. Pavan Kumar Associate Professor Department of Civil Engineering Vasavi College Engineering
Nature Of Rocks  Rocks are aggregate of one or more minerals  The nature and properties of rock are determined by the minerals in it and by the manner in which the minerals are arranged relative to each other (i.e., texture of the rock)  An individual rock type or specimen is always described in terms of its mineral composition and its texture  According to their manner of formation rocks are of three main types: Igneous rocks Sedimentary rocks Metamorphic rocks
Igneous Rocks Are formed from magma, which has originated well below the surface, has ascended towards the surface, and has crystallised as solid rock either on the surface or deep within the Earth’s crust as its temperature fell Sedimentary Rocks Are formed by the accumulation and compaction of: - Fragments from pre-existing rocks which have been disintegrated by erosion - Organic debris such as shell fragments or dead plants - Material dissolved in surface water or groundwater which is precipitated in condition of oversaturation Metamorphic Rocks Are formed from pre-existing rocks of any type, which have been subjected to increases of temperature (T) or pressure (P) or both, such that the rocks undergo change This change results in the metamorphic rock being different from the original parental material in appearance, texture and mineral composition
Igneous Rocks Mineralogy of Igneous Rocks Igneous rocks are formed from the cooling and solidification of hot and fluid mass of rock called magma that exists in the interior part of the earth Only about eight minerals are normally present as essential constituents of igneous rocks Which of the eight are present is primarily controlled by the composition of magma Intrusion of magma from deep-seated source (plutonic) or from moderate depth after solidification (hypabyssal) result in the formation of igneous bodies such as batholiths, laccoliths, phacoliths, lopoliths, which extend over a large part of the earth’s crust
D – Dyke – Discordant bodies that cut across the bedding of country rock (i.e., rock native to that area) L Lava Flow S – Sill- concordant bodies occurring parallel to the bedding plane
 The different types of intrusive igneous rocks can be described as follows: oBatholith is a very large discordant igneous body ranging from tens to hundreds of square kilometres in size. It can be spread irregularly over great depths. oPhacolith is a concordant igneous body that appears crescent shaped at its surface. oLaccolith is an intrusive igneous body that has a concordant relation with the country rock (native rock) and appears like a dome at its upper part. oLopolith is an intrusive igneous body that maintains a concordant relationship with the country rock and exhibits saucer-shaped appearance at the ground.
• Most igneous rocks are composed of an interlocking collection of crystals that grew as the magma cooled • When the magma is deep seated inside the earth, cooling is slow and crystallization takes considerable time; hence, the rock is coarse grained • If the magma is closer to the surface and intrudes through cracks in the crust (as in dykes), the cooling and crystallization process is comparatively rapid and the rock thus formed is fi ne-to-medium grained • Extrusive rocks – solidification of lava at the surface – cooling is very rapid; no time for crystallization – very fine textured rocks • Volcanic rocks – igneous rocks that originate from rapid cooling of lava under surface conditions • The vast area of Deccan Trap in India is formed of volcanic rocks created by lava flows
 Irrespective of the nature of texture, igneous rocks are classified on the basis of the proportion of the total silica in their composition  The more silica a rock has, the more acidic it will be  Hence on the basis of silica content, igneous rocks are classified into: Acidic (Felcic) Igneous Rocks - Contain more than 66% of silica - Constituent minerals of these rocks are: Feldspar and quartz in abundant amount; muscovite, biotite and amphibole in subordinate amounts - Example: Granite Intermediate Igneous Rocks - Silica content in these rocks is between 52% and 66% - Feldspars are abundantly present; biotite and amphibole are present in smaller quantities - Example: Diorite
Basic Igneous Rocks - Silica content is less than 52% (quartz is absent) - Rocks contain mostly feldspar and pyroxene with olivine - Example: Gabbro and basalt Ultrabasic Igneous Rocks - Silica content is less than 45% and the minerals are mainly olivine and pyroxene Granite Diorite Gabbro
Sedimentary Rocks Derived from pre-existing igneous, sedimentary or metamorphic rocks All existing rocks are subjected to the actions of water, wind, and ice that result in decay and disintegration of the rocks and formation of sediments This process is called denudation of rocks Sedimentary rocks may be composed of clastic (fragments of pre-existing minerals and rocks) or non-clastic (precipitated chemically from water) materials Sedimentary rocks provide information on the history of deposition and palaeo- environment The knowledge of origin of plants, animals, and man is obtained from the study of fossils embedded in sediments The most prominent primary structure of sedimentary rocks is the bedding or stratification of varying thickness as well as composition
The sedimentary rocks of Vindhyan formation in India are famous for architectural works from the prehistoric time and are even now used as construction material in various engineering projects
Metamorphic Rocks Metamorphic rocks are formed by the metamorphism of pre-existing rocks under high temperature and pressure conditions or by chemically-active fluids bringing about both physical and chemical changes in the original rocks Xenolith – a metamorphic rock which shows remnants of earlier rock from which it has formed The pattern of change depends upon the grade of metamorphism controlled by the pressure–temperature conditions In general, metamorphism takes place within a temperature range of 100°C to 900°C generated from the intrusion of plutonic rocks The pressure comes from the huge thickness of overlying rocks or forceful intrusion of plutons (a deep seated intrusion of igneous rocks) and plate collisions Hot water and other fluids associated with magma react with surrounding rocks to bring about chemical changes
Two most important forms of metamorphism: Contact or thermal metamorphism - Native rocks react with intrusive intrusive igneous bodies causing changes in the surrounding rocks as a result of the heat generated from intrusion or injection of magmatic fluids - The rocks produced by contact metamorphism are restricted to areas close to plutonic (deep-seated) bodies Regional Metamorphism - Regional metamorphism affects large regions such as the Precambrian shield and also cores of folded mountains - Example: Gneiss, schist, slate
During metamorphism, the effect of pressure causes growth of new crystals or reorientation of previously existing crystals to layers commonly known as foliation Foliation causes splits in rocks and hence has an important bearing in engineering geology related to metamorphic rocks On the basis of foliation, metamorphic rocks are classified into the following types: Slate: Fine grained; foliation is very closely packed. Phyllite: Fine grained; wavy or crenulated surfaces having sheen caused by small flakes of mica or chlorite. Schist: Coarse to medium coarse; undulating planes with abundant mica. Depending on the constituent minerals, this rock is designated as hornblende schist or garnet mica schist. Gneiss: Coarse; widely spaced foliation than schist, mainly occurring with bands of dark and light minerals in thin layers. Migmatite: Coarse; poor foliation showing signs of having begun to melt.
Properties of Rocks.pptx
Properties of Rocks.pptx

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Properties of Rocks.pptx

  • 1. Properties of Rocks Dr. K. Pavan Kumar Associate Professor Department of Civil Engineering Vasavi College Engineering
  • 2. Nature Of Rocks  Rocks are aggregate of one or more minerals  The nature and properties of rock are determined by the minerals in it and by the manner in which the minerals are arranged relative to each other (i.e., texture of the rock)  An individual rock type or specimen is always described in terms of its mineral composition and its texture  According to their manner of formation rocks are of three main types: Igneous rocks Sedimentary rocks Metamorphic rocks
  • 3. Igneous Rocks Are formed from magma, which has originated well below the surface, has ascended towards the surface, and has crystallised as solid rock either on the surface or deep within the Earth’s crust as its temperature fell Sedimentary Rocks Are formed by the accumulation and compaction of: - Fragments from pre-existing rocks which have been disintegrated by erosion - Organic debris such as shell fragments or dead plants - Material dissolved in surface water or groundwater which is precipitated in condition of oversaturation Metamorphic Rocks Are formed from pre-existing rocks of any type, which have been subjected to increases of temperature (T) or pressure (P) or both, such that the rocks undergo change This change results in the metamorphic rock being different from the original parental material in appearance, texture and mineral composition
  • 4. Igneous Rocks Mineralogy of Igneous Rocks Igneous rocks are formed from the cooling and solidification of hot and fluid mass of rock called magma that exists in the interior part of the earth Only about eight minerals are normally present as essential constituents of igneous rocks Which of the eight are present is primarily controlled by the composition of magma Intrusion of magma from deep-seated source (plutonic) or from moderate depth after solidification (hypabyssal) result in the formation of igneous bodies such as batholiths, laccoliths, phacoliths, lopoliths, which extend over a large part of the earth’s crust
  • 5. D – Dyke – Discordant bodies that cut across the bedding of country rock (i.e., rock native to that area) L Lava Flow S – Sill- concordant bodies occurring parallel to the bedding plane
  • 6.  The different types of intrusive igneous rocks can be described as follows: oBatholith is a very large discordant igneous body ranging from tens to hundreds of square kilometres in size. It can be spread irregularly over great depths. oPhacolith is a concordant igneous body that appears crescent shaped at its surface. oLaccolith is an intrusive igneous body that has a concordant relation with the country rock (native rock) and appears like a dome at its upper part. oLopolith is an intrusive igneous body that maintains a concordant relationship with the country rock and exhibits saucer-shaped appearance at the ground.
  • 7. • Most igneous rocks are composed of an interlocking collection of crystals that grew as the magma cooled • When the magma is deep seated inside the earth, cooling is slow and crystallization takes considerable time; hence, the rock is coarse grained • If the magma is closer to the surface and intrudes through cracks in the crust (as in dykes), the cooling and crystallization process is comparatively rapid and the rock thus formed is fi ne-to-medium grained • Extrusive rocks – solidification of lava at the surface – cooling is very rapid; no time for crystallization – very fine textured rocks • Volcanic rocks – igneous rocks that originate from rapid cooling of lava under surface conditions • The vast area of Deccan Trap in India is formed of volcanic rocks created by lava flows
  • 8.  Irrespective of the nature of texture, igneous rocks are classified on the basis of the proportion of the total silica in their composition  The more silica a rock has, the more acidic it will be  Hence on the basis of silica content, igneous rocks are classified into: Acidic (Felcic) Igneous Rocks - Contain more than 66% of silica - Constituent minerals of these rocks are: Feldspar and quartz in abundant amount; muscovite, biotite and amphibole in subordinate amounts - Example: Granite Intermediate Igneous Rocks - Silica content in these rocks is between 52% and 66% - Feldspars are abundantly present; biotite and amphibole are present in smaller quantities - Example: Diorite
  • 9. Basic Igneous Rocks - Silica content is less than 52% (quartz is absent) - Rocks contain mostly feldspar and pyroxene with olivine - Example: Gabbro and basalt Ultrabasic Igneous Rocks - Silica content is less than 45% and the minerals are mainly olivine and pyroxene Granite Diorite Gabbro
  • 10. Sedimentary Rocks Derived from pre-existing igneous, sedimentary or metamorphic rocks All existing rocks are subjected to the actions of water, wind, and ice that result in decay and disintegration of the rocks and formation of sediments This process is called denudation of rocks Sedimentary rocks may be composed of clastic (fragments of pre-existing minerals and rocks) or non-clastic (precipitated chemically from water) materials Sedimentary rocks provide information on the history of deposition and palaeo- environment The knowledge of origin of plants, animals, and man is obtained from the study of fossils embedded in sediments The most prominent primary structure of sedimentary rocks is the bedding or stratification of varying thickness as well as composition
  • 11. The sedimentary rocks of Vindhyan formation in India are famous for architectural works from the prehistoric time and are even now used as construction material in various engineering projects
  • 12. Metamorphic Rocks Metamorphic rocks are formed by the metamorphism of pre-existing rocks under high temperature and pressure conditions or by chemically-active fluids bringing about both physical and chemical changes in the original rocks Xenolith – a metamorphic rock which shows remnants of earlier rock from which it has formed The pattern of change depends upon the grade of metamorphism controlled by the pressure–temperature conditions In general, metamorphism takes place within a temperature range of 100°C to 900°C generated from the intrusion of plutonic rocks The pressure comes from the huge thickness of overlying rocks or forceful intrusion of plutons (a deep seated intrusion of igneous rocks) and plate collisions Hot water and other fluids associated with magma react with surrounding rocks to bring about chemical changes
  • 13. Two most important forms of metamorphism: Contact or thermal metamorphism - Native rocks react with intrusive intrusive igneous bodies causing changes in the surrounding rocks as a result of the heat generated from intrusion or injection of magmatic fluids - The rocks produced by contact metamorphism are restricted to areas close to plutonic (deep-seated) bodies Regional Metamorphism - Regional metamorphism affects large regions such as the Precambrian shield and also cores of folded mountains - Example: Gneiss, schist, slate
  • 14. During metamorphism, the effect of pressure causes growth of new crystals or reorientation of previously existing crystals to layers commonly known as foliation Foliation causes splits in rocks and hence has an important bearing in engineering geology related to metamorphic rocks On the basis of foliation, metamorphic rocks are classified into the following types: Slate: Fine grained; foliation is very closely packed. Phyllite: Fine grained; wavy or crenulated surfaces having sheen caused by small flakes of mica or chlorite. Schist: Coarse to medium coarse; undulating planes with abundant mica. Depending on the constituent minerals, this rock is designated as hornblende schist or garnet mica schist. Gneiss: Coarse; widely spaced foliation than schist, mainly occurring with bands of dark and light minerals in thin layers. Migmatite: Coarse; poor foliation showing signs of having begun to melt.