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PREPARED BY: MR: ALEX CHRISTOPHER ASSISTANT PROFESSOR DEP.OF CIVIL ENGG VELAMMAL ENGG. CLG. CHENNAI-66 VELAMMAL ENGINEERING COLLEGE UNIT – III PETROLOGY • • • • Classification of rocks Distinction between Igneous, Sedimentatary and Metamorphic rocks. Description occurrence, engineering properties and distribution of following rocks-Igneous rocks - Granite, Syenite, Diorite, Gabbro, Pegmatite, Dolerite and Basalt Sedimentary rocks sandstone, Limestone, Shale Conglo, Conglomerate and breccia. Metamorphic rocks, Quartzite, Marble, Slate, Thyllite, Gniess and Schist. VELAMMAL ENGINEERING COLLEGE Petrology: The branch of geology dealing the various aspects of rocks such as their formation, classification and occurrence is called petrology. Based on the formation, origin and chemical composition the rock can be classified into three classes. • Igneous rock • Sedimentary rock • Metamoraphic Rock VELAMMAL ENGINEERING COLLEGE IGNEOUS PETROLOGY What are Igneous rocks? The rocks that have been formed from an original hot, molten materials through the processes of cooling and crystallization, may be defined as igneous rocks. Formation of igneous rock The hot molten material occurring beneath the crust of the earth it is called magma.(when it comes out from the earth interior to the surface of the earth is called lava). During their journy it comes out on the earth surface and solid to from rock, this is called extrusive igneous rock some part of the magma may be arrested within the crust during their upward journey and solidifying to from rock it is called intrusive igneous rocks. The intrusive igneous rocks, which formed at great depth is called plutonic rock. The intrusive igneous rocks which formed at shallow depths is called hyp-aby sal rocks. So based on the modes of formation the igneous rock can be classified into three 1) Plutonic 2) Hyp – abyssal and 3) Volcanic rock. VELAMMAL ENGINEERING COLLEGE VELAMMAL ENGINEERING COLLEGE VELAMMAL ENGINEERING COLLEGE VELAMMAL ENGINEERING COLLEGE VELAMMAL ENGINEERING COLLEGE Average Chemical Composition of igneous rocks Sl No Oxide - % Sl No Oxide - % Sl No Oxide - % 1 SiO2 = 59.14 4 Fe2O3 = 3.08 7 Na2 = 3.84 2 Al2 = 15.35 5 CaO = 5.08 8 K2O = 3.13 3 FeO = 3.80 6 MgO = 3.49 9 H2O = 1.15 10 Others = 1.34 VELAMMAL ENGINEERING COLLEGE Average Mineralogical Composition Of Igneous Rocks Feldspars Biotite Pyroxenes and Amphiboles Titanium Quartz Apatite Accessory Minerals VELAMMAL ENGINEERING COLLEGE 59.54 3.82 16.85 1.53 12.06 0.67 5.8 FORMS OF IGNEOUS ROCKS Based on the mode of forms igneous rocks can be classified into different forms as follows Discordant Igneous Body If an intrusive mass happens to cut across the structure of the pre – existing rocks of the country , it is said to be a discordant body. VELAMMAL ENGINEERING COLLEGE Concordant igneous body: It an intrusive mass run parallel to the structure of the country rocks is called concordant. Dyke: Vertical formation of discordant intrusive igneous rocks are called dyke. VELAMMAL ENGINEERING COLLEGE Sills: Horizontal formation of intrusive igneous rocks are called sills. Radiating dykes: Dykes commonly occur in groups and such groups may exhibits radiating or arcuate. VELAMMAL ENGINEERING COLLEGE Ring dyke: An arctuate dyke occurring more or less in the form of a complete or nearly complete circular called as ring dyke. Cone sheet: Some time sheets of igneous materials are found to occur in the form of coaxial cones with thin layer of country rocks is called cone – sheet VELAMMAL ENGINEERING COLLEGE LACCOLITHS: Are discordant igneous bodies with their lower surface flat and upper surface arched in the form of a dome LOPOLITH: Are discordant igneous bodies with their shape more or less similar to that of a sancer. VELAMMAL ENGINEERING COLLEGE Pacolet: Concordant igneous bodies more are less crescentic in shape occurring along the crests and troughs of the fold of country rocks. Batholiths: It is an discordant igneous body of extremely large dimensions so much so that their exposed upon the surface. VELAMMAL ENGINEERING COLLEGE Sheet structure: The development of joints within the igneous rocks has often been found to bring about the formation of certain types of characteristic structure. Development of one set of well defined joints always brings about a slicing effect on the massive igneous rocks body if all such slices are horizontal, formed due to development of one set of closely spaced horizontal joints plants the structure is define as sheet structure Platy structure: Some times one of the different sets of joints developed in an igneous rock body may be so conspicuous that on striking the rock mass, only thin plates of rocks are broken off from the mass and this feature may be defined as platy VELAMMAL ENGINEERING COLLEGE structure. Columnar structure: Most of the extrusive igneous bodies the cooling of the mass brings about the development of a few sets of vertical joints. Such set of vertical joints of ten intersect and thus divide the rock mass into a number of vertical columns which may be square, rectangular, rhombic, trigonal etc., when an igneous rock mass is divide in this fashion into a number of vertical columns the structure is described as columnar structure. VELAMMAL ENGINEERING COLLEGE Block lava: Acidic lavas do not flow, due to their remarkable viscosity, to great distances and during solidification are found to often a very rough surface. Such lava flow is known as block lava. VELAMMAL ENGINEERING COLLEGE Roby lava: If the lava is fluid and during consolidation, the flow offers a smooth surface. it is described ropy lava. VELAMMAL ENGINEERING COLLEGE SEDIMENTARY ROCKS Natural agents like blowing wind, running water, peculating underground water, and glaciers in motion etc., are in ceaseless operation, causing continuous wear and tear of the rocks exposed to their fury. The products of such decay are subjected, under favorable condition to sedimentation and sequent compaction. The resulting rock masses thus formed under ordinary pressure temperature conditions are known as the sedimentary or secondary rock. VELAMMAL ENGINEERING COLLEGE • Compaction and cementation transform sediments into sedimentary rock. sedimentary rock • Most transported sediment settles out of a fluid and hence ends up being deposited in rivers, lakes and most of all in the oceans. • However, sediment is found almost everywhere.Geologists estimate that sedimentary rocks account for only about 5% (by volume) of Earth’s outer 16 kilometers.However, sedimentary rock is very important.The vast majority of rocks exposed at Earth’s surface are sedimentary. VELAMMAL ENGINEERING COLLEGE Classification of Sedimentary Rocks RESIDUAL SEDIMENTARY ROCKS: These rocks are formed due to accumulation and consolidation of those materials which were left as residue during the operation of the processes of weathering and transportion, common example are laterite, bauxite, etc., MECHANICAL SEDIMENTARY ROCK : These are formed due to deposition, under suitable conditions, of the pebbles, sand, silts etc., which were carried is suspension with the surface runoff. Common examples of rocks belonging to group are sandstone, conglomerate, grit, shale, mudstone, etc., CHEMICAL SEDIMENTARY: These are formed due to precipitation and consequent accumulation of the soluble constituents traveling along with the surface run-off. The precipitation may take place under a suitable chemical environmental or due to activity of organisms. ORGANIC SEDIMENTS: These are the products of accumulation of organic matter and are preserved under suitable conditions.(Example : coal, fossiliferous limestone, etc.,) VELAMMAL ENGINEERING COLLEGE Structures of Sedimentary Rocks Lamination : Layering, bedding or stratification is a very characteristic features of the sedimentary rocks. If the individual layers be extremely thin, the structure is known as lamination and the layers are described as laminae. Bedding plane : It is sedimentary sequence the surfaces separating the different beds are known as bedding plane. Fissility : Sometimes flaky minerals like mica lie parallel to the bedding planes of sedimentary layers and due to this reason, the rock may be easily fractured along the direction of bedding plane is known as fissility. Current bedding :The sedimentary beds are generally parallel to one another. Sometimes, however, within a sedimentary sequence, some of the beds may be Found to lie slightly oblique to the major bedding planes. This structure is known as current bedding. VELAMMAL ENGINEERING COLLEGE Torrential bedding : When deposition takes place in such a manner that thin horizontal beds, made up of fine materials, are found to lie in alternation with coarse and current bedded deposits, the resulting structure is known as torrential bedding. Delta structure :The deltas or river are formed due to deposition of sediments and show a characteristic structure of this own there are generally three sets of beds of which the upper and lower ones show a very gentle slope towards the sea, in conformity with the slope of the floor which they settle down. These are known as top set and bottom set beds .in between two sets lies the third set which exhibits a considerable amount of slope towards the sea. These are known as the forest beds. VELAMMAL ENGINEERING COLLEGE Ripple marks :These are the undulation surface of loose sediments due either to action of wide of waves in a shallow water – body. Mud cracks : In huge masses of fine – grained sediments, drying under sub – aerial conditions due to this processes the creaks are developed. This is known as mud – cracks these are also known as sun cracks since they are formed due to the effect of solar heat. Rain-Prints :These are formed on the top – surface of loose sediments many cause the development of markings, impressions or foot – prints, etc, which are known as tracks and trails. VELAMMAL ENGINEERING COLLEGE Sedimentary Rocks are Classified Sedimentary rock have been classified on the basis of their • • • • mineralogical composition environmental of deposition mode of formation texture and structural feature Clastic rock Gravel Sand Silt Clay Rudites Arenites Lutites Non clastic rocks VELAMMAL ENGINEERING COLLEGE Clastic rock • These rocks are also called as mechanically formed sedimentary rocks . • These kind of rocks are formed due to weathering, transportation and deposition of rock fragment by the natural agents like wind, water and ice etc., • Further the clastic rocks are classified based on the average grain size. Gravel: All the sediments and fragments or rocks irrespective of their composition and shape which are bigger than 2mm it is further divided into Boulders (256 mm) Cobbles (256mm –16mm) Pebbles (16mm 2 mm) Sand: The sand grain size between 2mm and 1/16 mm . it is further subdivide into Coarse sand (2mm to ½ mm) Medium Sand (1/2 mm to ¼ mm) Fine sand (1/4mm to 1/16 mm) Silt: These are very fine size particles in the size between (1/16mm – 1/256mm) Clay: All sedimentary particle fines in size than 1/256mm.Based on the predominance of sediments of a particular grade the clastic rocks are sub divide into following three major classes. VELAMMAL ENGINEERING COLLEGE 1. Rudites: These are also called as rudaceous rocks, it include all coarse grain clastic rocks having the grain size above 2mm clay is the common cementing materials (breccias and conglomerates) 2. Arenites: These are also called arenaceous rocks. These are mode up sediments of sand grade(2mm-1/16 mm) i.e. sand stone, Grey wackes and Arkose. 3. Lutites: These rocks are also called as argillaceous rocks. These rocks are made-up of very fine particles like silt and clay.(i.e. Shale’s, Clays and Mudstone) Non clastic rocks: This groups includes all those sedimentary rocks that have been formed by Operation of simple chemical processes such as evaporation, precipitation and crystallization of ordinary temperature and pressure. Accumulation of hard parts of organisms following by the compaction and consolidation. VELAMMAL ENGINEERING COLLEGE METAMORPHIC ROCKS The physical and chemical alteration of solid rocks that transform their texture, structures and mineral composition in response to change in their environment conditions within the earth. These are pre – existing rocks of igneous and sedimentary rocks that have been changed in texture , structure and mineral composition by physical and chemical processes, the physical changes include • Crushing of grain • Recrystallization • Interlocking of grain VELAMMAL ENGINEERING COLLEGE CAUSES OF METAMORPHISM Pressure : The pressure is either vertical rocks load, causes by the weight of overlying rock. Hydrostatic pressure of inter granular fluids. Both types of pressure increase when increase the depths . The dynamic or unbalanced tangent pressure associated with tectonic movement . Heat : The heat may be earth heat, associated with the thermal gradient that is a heat increase of 20 C per KM of depth. Fluids :The active fluids includes not gases, especially stream and carbon dioxide and hot solutions conditions the ions of common elements such as sodium and calcium. VELAMMAL ENGINEERING COLLEGE CLASSIFICATION OF METAMORPHISM Thermal metamorphism: Heating of rocks buried to great depths or adjacent to igneous intrusions and extrusions includes recrystallization. Conversion of limestone into marble take place due to thermal met amorism this is called thermal metamorphism. Contact metamorphism : Metamorphism suffered by the country rock, in the neighborhood and due to the heat of an igneous intrusive body, is called as contact metamorphism and the region around the igneous body within which such metamorphism is in operation, is known as the contact aureole. Pyrometamophism: Due to access of chemically reactive substance from the igneous body and their reaction with the country rocks , the processes of contact metamorphism passes on to which is known as pyrometamorphism. Optalic metamorphism: Burning of the country rocks along the fringing of minor igneous intrusive is defined as Optalic metamorphism . VELAMMAL ENGINEERING COLLEGE • Hydrothermal metamorphism :This type of metamorphism is produced by hot magmatic water that have been heated mobilized and chemically changed by igneous intrusions. • Plutonic metamorphism: The uniform pressure and temperature can change in mineral composition and texture of rocks and the nearly formed minerals are such that the resulting mass commonly suffers a reduction in volume . • Cataclastic metamorphism : Direct pressure or stress can dominate at or near the surface where lateral forces, leading to mountain – building are in plug due to this process the texture of the rock changed , this kind of metamorphism is known as cataclastic metamorphism. • Dynamo thermal metamorphism: It is also called as regional metamorphism. This involves development of large scale changes in the structural and chemical constitution of the pre – existing rocks under the combined action of pressure , temperature and fluids. Such conditions are available during the mountain building activity in the history of the earth. VELAMMAL ENGINEERING COLLEGE Igneous Rocks Sedimentary Rocks These are the products of consolidation of magmas Formed due to eruption and solidification or cooling of magma. Based on the formation, it can be classified into two type intrusive igneous rock and extrusive igneous rocks. Internal forces operate the formation of igneous rocks. (ie. Volcanos, arthquake and tectonic movement) Occurrence of mineral grains igneous rocks can be classified into polycrystalline and hemi crystalline . Granite, diorite, syenite, gabbro and dolerite are the common igneous rocks. This kind of rocks are also called Primary Rocks Sedimentary rocks are the products of weathered igneous Rocks. Formed due to deposition and cementing of weathered rock material on the surface of the earth due to pressure. Based on the formation it can be classified into 1. residual sedimentary rocks, 2.mechanical sedimentary rock 3.chemically formed sedimentary rock and organic sedimentary rocks External agents such as running water, glacier, wind, sea water, etc.,are the force which operate the formed of sedimentary rocks. Based on the grained size it can be classified into rudaceous, arenaceous and argillaceous rocks. Breccias, Conglomerates, Sandstone, Shale’s, Limestone, Bolomite and Coal are the common sedimentary rocks. This kind or rocks are also called as secondary rocks VELAMMAL ENGINEERING COLLEGE Metamorphic rock Metamorphic rocks are the products of the igneous and sedimentary rocks Formed due to change of texture, structure and mineral composition by physical and chemical processes. Based on the formation these rock can be classified into thermal metamorphism, dynamic metamorphism and dynamo thermal metamorphism. Physical and chemical agents such as 1.temperature 2.pressure 3.stree and 4.chemical reactive substances operate the formation of metamorphic rocks. Based on the texture, structure and mineral composition, metamorphic rocks can be classified into foliated and non – foliated rocks Slate, gneiss, schist, quartzite’s, morble, phyllite and hornfels are the common metamorphic rocks. VELAMMAL ENGINEERING COLLEGE IMPORTANT SEDIMENTARY ROCKS • Breccias • Conglomerate • Stand stone • Shale • Lime Stone VELAMMAL ENGINEERING COLLEGE Breccias • It is a mechanically formed sedimentary rocks. • It consists of angular rock fragments embedded in a fine matrix of clayey material. • The fragments are generally greater than 2mm in average diameter. • Breccias are further classified in to basal breccias , fault breccias and agglomerate breccias. Basal Breccias This is formed by the sea water advancing over a coastal region covered with fragments of rocks. The advancing waters supply the fine mud, which spread over the rock fragment and act as a binding material. Once the sea water retreats the rock fragment get cemented together to form breccias. VELAMMAL ENGINEERING COLLEGE VELAMMAL ENGINEERING COLLEGE Fault Breccias or Crush Breccias The angular and clay like rock materials are produced during the processes of faulting. Subsequently get embedded in clay and form a cemented rocks. VELAMMAL ENGINEERING COLLEGE Agglomerate Breccias or Volcanic Breccias •This kind of sedimentary rocks formed by the volcanic eruptions. •The angular and fused rock materials cemented to form rocks. VELAMMAL ENGINEERING COLLEGE Conglomerate • These are sedimentary rocks of elastic nature and belonging to rudaceous group. • They consist of rounded fragments of various sizes but generally above 2mm cemented together in a clayey matrix. Based on Grain Size the Conglomerate can be classified in to: • • • Boulder (gravel > 256mm) Cobble (gravel 64-256 mm) Pebble (gravel 2 – 64 mm) Based on Source of Gravel • • • Basal conglomerates Glacial conglomerates Volcanic conglomerates VELAMMAL ENGINEERING COLLEGE VELAMMAL ENGINEERING COLLEGE VELAMMAL ENGINEERING COLLEGE Stand stone • It mechanically formed sedimentary rocks of arenaceous group. • These are mostly composed of sand grade partials. • The grain size between 1/162 – 2mm . • Si O2 is the dominate mineral in sandstone. Texture : Sand stone are medium to fine – grained in texture. Color : Stand stone show a variety of colors ,red , brawn, gray and white being the common. Types : Siliceous, calcareous, argillaceous and ferruginous sandstones are the common types of sandstone. Uses : Sandstone of hard, massive and compact character are most commonly VELAMMAL ENGINEERING COLLEGE used as building stones. VELAMMAL ENGINEERING COLLEGE IMPORTANT METAMORPHIC ROCKS • Quartzite • Marble • Slate • Phyllite • Gneiss • Schist VELAMMAL ENGINEERING COLLEGE QUARTZITE : It is a granular metamorphic rocks composed chiefly of quartz grains. It is a granular rock characterized by a tendency of fracturing through the grains rather than along the grains under heavy load Composition : it is a mixture of mica feldspars, granet and some amphiboles. Origin : Metamorphic quartzite’s result from the recrystallisation of pure sandstones under the influence of contact and dynamic metamorphism. Uses : The rock is generally very hard strong, dense and uniformly grained. it using in building and roads construction VELAMMAL ENGINEERING COLLEGE QUARTZITE VELAMMAL ENGINEERING COLLEGE SLATE : Slate is an extremely fine – grained metamorphic rock characterized by a slaty cleavage by virtue of which it can be split into thin sheets with parallel smooth surfaces. Composition: Mineralogically, slate is composed of very fine grains of micas, chlorite, quartz, felspers, oxides of iron and many other minerals all of which cannot be easily identified even under microscope because of their fine grain size. Origin : Slate is the product of low – grade regional metamorphism on argillaceous rocks like shales. When slate is subjected to further action of dynamo thermal metamorphism, recrystallisation may lead to the development in number and size of stone minerals, especially micas. Uses : Slate is locally used as a roofing material. It cannot be as a building stone or road stone because of its low crushing strength and slaty cleavage. VELAMMAL ENGINEERING COLLEGE SCHIST VELAMMAL ENGINEERING COLLEGE SCHIST : These are megascopically crystalline metamorphic rocks characterized by a typical schistose structure. Texture and structure : Most varieties are typically schistone in structure and megascopically crystalline in texture. Composition : Micas, chloride, talk, hornblende, tremolite and kyanite are quite common constituents of many schists. Varieties : muscovite schist ,biotite schist and tourmaline schist etc. Origin : Schists are generally the produced of dynamo thermal metamorphism. VELAMMAL ENGINEERING COLLEGE SCHIST VELAMMAL ENGINEERING COLLEGE GNEISS: A gneiss is a megascopically crystalline metamorphic rock. A typical gneiss will show bands of mica and other play minerals alternating with bands of equidmensional minerals like felspars, quartz, garnet etc., Composition : Felspars and quartz are more common in gneisses then in schists. Dark minerals of amphibole and pyroxene groups are also common as are the typically metamorphic minerals like staurolite, sillimanite, garnet,kyanite and epidiote etc., Structures : Gneissose structure and Cataclastic structure. Origin : Gnesses are generally the product of advanced stages of metamorphism of a variety of parent rocks such as sandstone, conglomerates and granites. Uses : Compact, dense, massive varieties of gneisses are used as building and road stones. VELAMMAL ENGINEERING COLLEGE VELAMMAL ENGINEERING COLLEGE GNEISS MARBLE : Marble is essentially a granular metamorphic rock composed chiefly of recrystallized calcite Compostion : CaCO3 Small amount of many other granular minerals like olivine, serpentine, garnet and some amphiboles are also present in many varieties. Varieties : Various types of marbles are distinguished on the basis of their color, composition and structure. Origin : marbles are formed as a result of carbonate rocks chiefly limestone and sometimes dolomites – under conditions of contact metamorphism. Uses : Marbles are commonly used in building construction in the form of blocks, slabs, arches and as chips for flooring. In most cases the stone is used for decorative and ornamental purpose. VELAMMAL ENGINEERING COLLEGE MARBLE VELAMMAL ENGINEERING COLLEGE PHYLLITE : It is a medium to fine grained metamorphic rock of complex silicate composition. Composition : Phyllites consist chiefly of chloride, muscovite and quartz grains all of which are in fine state, but can be seen with a hand lense. In fact this is the main point of difference between slates and phyllites. Origin : Phyllites are formed in nature as a result of dynamo- thermal metamorphism of clay bearing rocks like shale. VELAMMAL ENGINEERING COLLEGE PHYLLITE VELAMMAL ENGINEERING COLLEGE IMPORTANT IGNEOUS ROCKS Granite : Granite is plutonic light colored igneous rocks and equigranular texture. Composition: Ouarts, orthoclase feldspar, albite feldspar, oligoclase and microcline. Associated minerals like mica, bioteie, hornblend, augite and hypersthene. Texture: It is coarse grained, holocrystalline and equigranular rocks Granular, graphic, porphyritc and intergrowth texture are common. Types: Muscovite-granite, biotite-granite, Muscovite biotite-granite, hornblend – granite, augite-granite and tourmaline – granite. Occurrence : It is most commonely distributed igneous rocks in the crust. It occur chiefly as deep-sheeted intrusive body likesills, dyke, bosses, stocks and batholiths. Use: Architexturaland massive construction VELAMMAL ENGINEERING COLLEGE VELAMMAL ENGINEERING COLLEGE Diorite: It is intermediate type of plutonic igneous rocks with high silick percentage. Composition: It is typically rich in feldspar plagioclase of sodic group, hornblend, biotite and pyraxene are associated minerals. Texture: Course to medium grain and holocrystalline texture. Occurrence: Commonely occur as intrusive bodies of dyke, sill, stocks and other intrusives. Use: Architexturaland massive construction VELAMMAL ENGINEERING COLLEGE Syenites: It is plutonic, even grained igneous rocks. Alkaline feldspar are the chief constituent minerals. Composition: Feldspar is the common mineral Texture: medium to course grained , holocrystalline nature. Gabbro: It is a coarse-grained, dark colored, plutonic intrusive igneous rock Composition: It contains feldspar, augite and sometimes olivine Texture: Coarse to medium grain and reaction rim. Diorite: is a grey to dark grey intermediate intrusive igneous rock Composition: composed principally of plagioclase feldspar, biotite, hornblende, and pyroxene. It may contain small amounts of quartz, microcline and olivine. Zircon and apatite. Texture: Course to medium grain and holocrystalline Occurrence: Occur as small VELAMMAL intrusive ENGINEERING bodies like dyke, sills, stocks etc COLLEGE Diorite Gabbro Dolerite: These are hypabyssal igneous rocks formed as shallow sills and dykes. Composition: calcic plagioclase, augite, olivine, iron etc. Texture: Medium to fine grained rocks VELAMMAL ENGINEERING COLLEGE