Lecture Notes: Rocks and Minerals Part 1 PDF

Chapter 2 Rocks and Minerals Part 1  Learning Contents Classification of rocks. Description and occurrence of rocks. Properties and distribution of rocks. The recycling of rocks  Earth’s Molten Stage – During the early formation of the Earth it was molten – During this...

Chapter 2 Rocks and Minerals Part 1  Learning Contents Classification of rocks. Description and occurrence of rocks. Properties and distribution of rocks. The recycling of rocks  Earth’s Molten Stage – During the early formation of the Earth it was molten – During this stage the heavier elements such as iron and nickel, sank to the deeper interior of the Earth. – This left a thin layer of lighter materials on the surface that is mow called the crust. – The majority of the Earth’s mass lies below the crust  Chemical Analysis – 8 elements make up 98.6% of the crust – These 8 elements make up the solid materials of the Earth’s crust and are known as rocks and minerals. – A mineral is solid inorganic material of the Earth that has both a known chemical composition and a crystalline structure that is unique to that mineral – A rock is a solid aggregate of one or more minerals that have been cohesively brought together by a rock- forming process.  (A)The percentage by weight of the elements that make up Earth's crust. (B) The percentage by weight of the elements that make up the whole Earth.  Rock Formation Geological cycle includes many processes acting simultaneously. The most important of these begin with molten magma from within the earth forming into rock, then continues with rocks being broken down into soil, and that soil being converted back into rock. 6 EARTH’S CRUST – Rocks and Minerals  The earth’s crust is composed of rocks.  Rocks are primarily composed of minerals (but may also contain organic materials).  The granite and basalt rocks of the continental and oceanic crusts were the original, igneous rocks. What is a Rock?  A rock is an aggregate of mineral particles – but may also contain organic materials  So, minerals are essentially the building blocks of rocks  Bedrock → Outcrop → Regolith → Soils Rock Classification Igneous Rocks form due to the cooling and crystallization of magma Sedimentary Rocks form through lithification of sediments from other rocks Metamorphic Rocks form via recrystallization of other rocks due to heat, pressure, and chemical alteration IGNEOUS ROCKS Igneous Rocks Are Subdivided into Two Classes:  Volcanic (Extrusive) Igneous Rocks  Volcanic extrusive igneous rocks form on earth's surface as lava cools  Basalt  Basalt is the most widespread volcanic rock  It is a dark, fine-grained rock  Basalt is the rock of the sea floor  Plutonic (or Intrusive) Igneous Rocks  Plutonic igneous rocks form deep underground where magma cools slowly; these rocks have a coarse crystalline texture  Granite  Granite is the most widespread of plutonic igneous rocks. It underlies much of the continental crust. Classification of Igneous Rock: Hypabyssal Rock: Hypabyssal rocks are formed when consolidation of magma takes place very close to the earth’s surface in the form of smaller sheet like bodies (known as sills and dykes) that fill cracks inside other rocks. Some extrusive generally have finer grained, smoother surfaces. Some extrusive materials, such as volcanic ash, bypasses the rock stage and forms directly into sediment 11  Dike and Sill igneous rocks Sill: A sill is igneous rock which vary in thickness from a few centimeter to several hundred meters. The sill is parallel to the bedding of rock and may be horizontal, inclined or vertical depending upon the strata. Dike: A dike is vertical wall-like igneous body that cuts the bedding of the rock. The thickness of the dike may vary from a few centimeters to a hundred meter or more. Igneous Rocks Common Igneous Rock: Some common igneous rocks include: Granite: is coarse grained, an intrusive rock. It is the most common and familiar igneous rocks. Granite contains primarily orthoclase feldspar and quartz, with some biotite and amphibole. It is mostly light in color with a white or pink tint according to the color of the feldspar. Engineering properties: Granite have absorption as low as 0.24 per cent. It has an excellent frost resistance. Because of the minerals composition and interlocking of crystals, granite is hard and abrasion resistant. The compressive strength of granite is on average 24,500 psi. Granite can be used to support any load of ordinary structures. Granite is also used as tiles for flooring in buildings. Common Igneous Rock:  Diorite: is coarse grained, an intrusive rock. It is mainly composed of plagioclase feldspar (more than 50 %) and hornblends. However, in some varieties augite and biotite may be present. It is more abundant than syenites but less abundant than granite. Diorite has been used for crushed stone for monumental and decorative purposes than for structural purposes.  Syenite: is grained igneous rocks composed essentially of potassium felspare (80-85 %). Biotite and hornblende are commonly present. Quartz is present in small amount. The general properties of syenites is similar to granite. Because of the rarity of syenite, it is of little commercial use as structural material. Composition of some igneous rocks Texture of igneous rocks  Texture: Texture is size, shape and arrangement of mineral grains in a rock. Texture of rock can either of coarse-crystalline or it can be glassy or amorphous. The texture of the rock is governed by the cooling time of the magma. Crystallization is governed by slow cooling, however, glassy texture or amorphous form is the result of rapid cooling.  Types of rock: Holocrystalline, Coarse grained, fine grained, cryptocrystalline and glassy (amorphous) Texture and color of igneous rocks  Igneous rock classification scheme based on mineral composition and texture. There are other blends of minerals with various textures, many of which have specific names.  Granite is a coarse-grained igneous rock composed mostly of light-colored, light-density, nonferromagnesian minerals. The earth's continental areas are dominated by granite and by rocks with the same mineral composition of granite.  This is a piece of obsidian, which has the same chemical composition as the granite. Obsidian has a different texture because it does not have crystals and is a volcanic glass. The curved fracture surface is common in noncrystalline substances such as glass.  The Importance of Igneous Rocks in Engineering Plutonic rocks often become resistant to breakage and pressure when they are fresh and although the rock is fractured. Therefore they show high resistance. They can be used in material engineering services when their resistance is between 1500-2000kg/cm2. The resistance of the rock depends on weathering and hence degradation degree will vary inversely with the degree of weathering. The Importance of Igneous Rocks in Engineering Since the volcanic masses have different physical properties, it is necessary to thoroughly inspect them before construction starts. Some lavas, agglomerates and volcanic rocks protect their freshness, so their resistance maybe as high as deep rocks such as basalt. But volcanic tuffs and breccias are hollow and decayed, so they show a drossy structure. At the same time they lose credibility because they show clay mineralization. SEDIMENTARY ROCKS Most sedimentary rocks are formed of layers of materials that have washed into lakes, rivers and oceans – Sedimentary rocks form strata Often layers are tilted by earth movements Sedimentary rocks contain fossils How do sediments turn into hard rock?  Through Lithification Processes:  Compaction  Cementation  Crystallization  Sedimentary rock is formed by deposition and consolidation of minerals and organic materials and from precipitation of minerals from solution.  The processes that form sedimentary rock occur at the surface of the earth and within bodies of water.  Rock formed from sediments covers 70-80 % of the earth’s land area, and includes common types such as limestone, chalk, sandstone, conglomerate and shale. Fromation of Sedimentary Rocks: Consolidation is a process by which soft and loose sediments are converted into hard and firm rocks. Consolidation is of three types: 1. Compaction and Dehydration: The squeezing out of water from the pores of the sediments and its changing to solid mass by cohesion between the particles and pressure from overlying rock is called compaction and dehydration. 2. Cementation: Many coarse grained sediments are consolidated by cementation, which is the process of precipitation of some cementing materials, for example, silica, calcium carbonate, iron oxides and clay minerals. 3. Crystallization: Chemically formed sedimentary rocks such as limestone, dolomites, gypsum etc are consolidated chiefly by the crystallization of their constituents. – Compaction As sediments are laid down grain by grain, the mass becomes greater. The increasing mass of the sediment layer above creates pressure on the layers below. Eventually this pressure becomes great enough to compact the existing layers into a cohesive rock layer. – Cementation After, or during, the compaction process, the spaces between the sediment particles become filled with a chemical deposit. This deposit holds the compacted layers into a cohesive mass of sedimentary rock.  Sedimentary Rocks – Form from material from previously existing rock Material is provided by weathering of previously existing rock – Sediments Weathered rock materials Dissolved rock materials – Clastic sediments Another name for weathered rock materials – Chemical sediments Another name for dissolved rock material. The dissolved materials are ions from mineral and rocks that have been completely broken down. Removed from solution by: –Chemical precipitation from the solution –Crystallization from evaporating water. –Biological sediments. Classification of Sedimentary Rocks: 1. Clastic: form from bits and pieces of other rocks 2. Chemical: consist of minerals deposited from a solution 3. Organic: consist of organic matter such as plants and animal remains Organically-formed sedimentary rocks form from the remains of plants and animals (fossil limestone, coal) Classification of Sedimentary Rocks: Mechanically (Clastic) formed: consisting of materials (gravels, sand, silt and clay) suspended in flowing water. The suspended materials are then deposited and consolidated. The mechanically formed sedimentary rocks are of three types: 1. Rudaceous rocks which is the cementing together of boulders, for example, conglomerate. 2. Arenaceous rocks for example sandstone, 3. Argillaceous rocks which is clay rocks for example shale Organically formed: Consisting of accumulated animals and plants remains. They are: 1. Calcarious rocks, lime stone 2. Carbonaceous rocks, coal Chemically formed: this type of rocks is formed by precipitation and accumulation of soluble constituents. These are 1. Carbonate rocks, Limestone, dolomite 2. Sulphate rocks, Gypsum 3. Chloride rocks, salt Formation of different types of Sedimentary Rocks Texture and Formation of Sedimentary Rocks Sedimentary Rocks Common Sedimentary Rock:  Conglomerate: The pebbles and gravels on consolidation and cementation produce a rock known as conglomerate. Gravels are deposited for the most part by water. Water circulating through gravel deposits may precipitate out silica, calcium carbonate, or iron oxides, which act as cements binding the gravels together into conglomerates.  Sandstones: Most sand is a water deposit. In arid regions, widespread sands have been laid down by wind action. Volcanic eruptions, glacial action, mechanical and chemical weathering, and organisms produce sands. The sand particles are deposited and then cemented together by materials like silica, calcite, iron oxide or clay. Sandstones may be siliceous sandstone that is the cementing materials is silica; it may be calcarious sandstone in which the cementing materials is calcium carbonate; ferruginous sandstone and argillaceous sandstone having iron oxide and clay as cementing materials.  This is a sample of breccia, a coarse-grained sedimentary rock with coarse, angular fragments. Compare the grain sizes to the centimeter scale.  This is a sample of sandstone, a sedimentary rock that formed from sand grains in a matrix of very fine-grained silt, clay, or other materials. The grains in this sample are mostly the feldspar and quartz minerals, which probably accumulated near the granite from which they were eroded.  Common Sedimentary Rock:  The thoroughly cemented sandstone with quartz are termed as orthoquartzite. Argillaceous rocks: variously called mudstone, claystone, and shale (compacted or cemented) are among the most abundant of sedimentary rocks. It is a laminated fine grained sedimentary rock which is mainly composed of clay minerals and some silt-size grains of quartz.  The claystones, because they are characteristically soft and weak are not suited to most construction purposes. The compacted shale lose strength when wet and are subject to plastic deformation. Under load they are subject to failure by flow. The cemented shales have a strength comparable to concrete but have a relatively high elasticity. Clay stones underlying the sites of heavy structures should be test in both wet and dry conditions. Clay stone has a limited use. It serves as a raw materials for the ceramic industry in some places and also used as raw materials for cement production. Common Sedimentary Rock:  Carbonate rocks: The carbonate rocks are chiefly the products of marine or fresh water sedimentation. They are predominantly chemical sediments either formed by metabolic process of organism or precipitated inorgainically. Mineralogically, the carbonate rocks are comparatively simple. There are two main varieties; the limestone composed chiefly of the calcite, and the dolomite composed chiefly of dolomite.  The carbonate rocks, particularly the limestones, have a very wide use in modern industry. The largest single use is as crushed stone. Limestone is one of the leading dimension stones being utilized both for internal and external work. Commercial lime is derived from the burning of limestone.  This is a sample of limestone, a sedimentary rock made of calcium carbonate that formed under water directly or indirectly from the actions of plants and animals. This fine- grained limestone formed indirectly from the remains of tiny marine organisms.  Structural Features of Sedimentary Rocks: Structural features of sedimentary rocks are of great value in determining their origin. The main structures are as follows: Stratification: The deposition of sediments into layer or beds is called stratification. The thickness of a single bed may vary from a few centimeters to many meters. The stratification is formed due to the following. I. Difference in the kinds of materials deposited for example shale and lime stone II. Difference in the size of particles deposited for example coarse grained and fine grained sandstone beds III. Difference in the color of the materials deposited for example light grey and dark grey layers of limestone Lamination: Thin bedding, less than one centimeter in thickness, are called lamination. It is usually fined grained sedimentary rocks like shales. Cross-bedding: It is also called current bedding or false bedding. Cross-bedding are the minor bedding or lamination which lie at an angle to the planes of general stratification. This structure is found in shallow water and wind formed deposits.  (A)In compaction, the sediment grains are packed more tightly together, often by overlying sediments, as represented by the bricks. (B) In cementation, fluids contain dissolved minerals that are precipitated in the space between the grains, cementing them together into a rigid, solid mass.  Textures of Sedimentary Rocks Grain sorting: Sorting refers to the uniformity of grain size in a sediment or sedimentary rock. Rounding: During the transportation process, grains maybe reduced in size due to abrasion. Random abrasion results in the eventual rounding off of the sharp corners and edges of grains. Thus, the degree of rounding of grains gives us clues to the amount of time a sediment has been in the transportation cycle. Sphericity: It is controlled by the original shape of the grain. The longer the sediment is transported, the more time is available for grains to lose their rough edges and corners by abrasion. Layering(bedding): One of the most obvious features of sedimentary rocks and sediment is the layered structure which they exhibit. The layers are evident because of differences in mineralogy, clast size, degree of sorting, or color of the different layers. In rocks, these differences maybe made more prominent by the differences in resistance to weathering or color changes brought out by weathering.  Textures of Sedimentary Rocks Cross Bedding: Consists of sets of beds that are inclined relative to one another. The beds are inclined in the direction that the wind or water was moving at the time of deposition. Boundaries between sets of cross beds usually represent an erosional surface. Cross bedding is very common in beach deposits, sand dunes, and river deposited sediment. Individual beds within cross-bedded strata are useful indicators of current direction and tops and bottoms. Note how the beds become asymptotic to the lower boundary on which they were deposited. Graded Bedding: As current velocity decreases, the larger or more dense particles are deposited first, followed by smaller particles. This results in bedding showing a decrease in grain size from the bottom of the bed to the top of the bed. This gives us a method for determining tops and bottoms of beds, since reverse grading will not be expected unless deposition occurs under unusual circumstances. Note that reverse graded bedding cannot occur as current velocity increases, because each layer will simply be removed as the current achieves a velocity high enough to carry sediment of a particular size.  Engineering Properties of Sedimentary Rocks Physical and especially mechanical properties of the existing rocks should be determined by laboratory tests and tests. The results should be numbered and used in basic and static calculations. The rocks have a certain carrying power. Rocks that are overloaded by forces change structure and shape, so the upper structures can be damaged. The ground that is overloaded on the surface shows different physical and chemical properties. The factors affecting the cost and safety of the construction which are known as the engineering properties of the rocks are the specific gravity, porosity, water absorption, unit volume weight, resistance corresponding to the press, resistance to atmosphere effect, wear, fragmentation.  Engineering Properties of Sedimentary Rocks With laboratory experiments; It should be determined whether they are essential or not according to various rock and soil conditions. Stability and resistance to depression should be determined. The properties of storage (S) or permeability (K) and transmissibility (T) of groundwater of various rocks and soils should be determined. Whether or not the rocks are suitable for building materials should be determined.  The resistance of the sedimentary rocks to breakage and pressures varies depending on the hardness grades and the susceptibility of the minerals to water. For example; Clay, marl, gypsum and limestone cemented sand stones and conglomerates show little resistance to water pressures. Silica cemented ones are more resistant, like granite and basalt. Good cemented rocks have high porosity and permeability ratings, so their water storage capacities are high, while their resistance is low.  Sedimentary rocks containing clay minerals such as clay and shale contain water in a small or large amount depending on the type of minerals they contain. Their indentations loosen or degrade according to the water content.As a result, resistance and handling power are reduced.  Engineering Properties of Sedimentary Rocks Limestones are used as building material for producing lime, aggregate, gravel and building stone. The resistance of the lime stones to be used in this area must be at least 200kg/cm2 with respect to water absorption, less abrasion, and pore and porosity The resistance of the limestones is low and high, so the stratification of the limestones is effective. Cracking systems and melting gaps should be avoided or minimized in limestones if they are used in foundation and dam construction. Limestones must be cracked and melting space at ground water investigations. Limestones which have high porosity and cracked provides to generate high disharges karstic springs. METAMORPHIC ROCKS Metamorphic rocks are rocks that have been changed in form due to heat, pressure, and chemical alteration. FOLIATED NONFOLIATED Slate Marble Schist Quartzite Gneiss Slate: forms when shale is compressed by heat and pressure; splits easily Schist: dominated by platy or needle-like minerals that form shiny layers Gneiss: under pressure the minerals in granite recrystallize to form bands of light and dark minerals Marble: Limestone recrystallizes into marble – a denser and more crystalline form of calcite Quartzite: Sandstone changes into quartzite; Sand grains recrystallize to form a hard mass of quartz Metamorphic Rocks  Metamorphic Rocks – Rocks changed by heat, pressure, or hot solutions due to: Movement of the Earth’s crust Heat generated by intrusion of hot magma Pressure can change rock by flattening, deforming, or realigning mineral grains. – Foliation When the pressure on flat crystal flakes tends to align the flakes into parallel sheets. Gives the rock the property of breaking along the planes between the aligned mineral grains in what is known as rock cleavage. Types of Metamorphism  Types of Metamorphism Contact or thermal metamorphism Driven by a rise in temperature within the host rock Regional metamorphism Occurs during mountain building Produces the greatest volume of metamorphic rock Burial metamorphism Occurs at bottom of thick sedimentary rock piles Hydrothermal metamorphism chemical alterations from hot, ion-rich water Effect of temperature in metamorphism  Increasing metamorphic change occurs with increasing temperatures and pressures. If the melting point is reached, the change is no longer metamorphic, and igneous rocks are formed.  Metamorphic Rock Textures 1.Foliated Rock - Bands of minerals in parallel layers Foliation –any planar arrangement of mineral grains or structural features within a rock Parallel alignment of platy and/or elongated minerals Foliation can form through: Rotation of platy and/or elongated minerals Recrystallization of minerals in the direction of preferred orientation Changing the shape of equidimensional grains into elongated shapes that are aligned 2. Non-foliated Rock - Without bands Metamorphic rocks that lack foliation are referred to as non- foliated Develop in environments where stress (deformation) is minimal Typically composed of minerals that exhibit equidimensional crystals.  This is a sample of marble, a coarse-grained metamorphic rock with interlocking calcite crystals. The calcite crystals were recrystallized from limestone during metamorphism.  This banded metamorphic rock is very old, it is probably among the oldest rocks on the surface of the earth.  Engineering Properties of Metamorphic Rocks Rocks showing foliation should not be preferred as construction materials in terms of strength. The strengths of the foliated metamorphic rocks, along with the leavening and foliations that develop as a result of the metamorphism, are decreasing along the foliage planes due to clay minerals that swell in water like chlorite and epidote. Marbles from metamorphic rocks are preferred as a good building material. It is the building material that is required in the building coverings. The metamorphic masses provide a solid structure for the foundation of the building, if it is not separated. Some slip planes can be used without any support if the slip gaps are not full with clays.  Engineering Properties of Metamorphic Rocks Metamorphics can be exposed to change immediately under favorable climatic conditions. Due to the changing construction, volume increases and pressure increases. Such features should be observed in tunnels and dam constructions and other constructions. Schist rocks along the schistosity plane cause shifts in the excavations. This is especially the case for the dissociated regions where the schistose and cleavage are opened and weakened and the rock resistance is greatly reduced. Schists and similar rocks create landslide hazards in road constructions, dam abrasions and reservoirs lopes.  Engineering Properties of Metamorphic Rocks Massive gneisses provide very good conditions for large underground openings. Facilities for swimming pools, theaters, skating rinks, industrial warehouses, production plants and many other activities have been created economically and safely in large openings to such rocks. Schistosized and competing gneisses can create stability problems in underground openings. Even in the ravaged schist and the small tunnels opened in the phyllite, the ceiling may collapse. As the metamorphic rocks are cracked and contested on the surface, excavations cause the rock blocks to move. HOW ROCKS RECYCLE ?  The rock cycle is a general model that describes how various geological processes create, modify, and influence rocks  The origin of all rocks can be ultimately traced back to the solidification of molten magma  Magma consists of a partially melted mixture of elements and compounds commonly found in rocks  Magma exists just beneath the solid crust of the Earth in an interior zone, the mantle  The Rock Cycle shows how rocks of any rock class can be recycled into rocks of any other rock class. The Rock Cycle Stages in the Rock Cycle  All rock types physically and chemically decomposed by a variety of surface processes collectively known as weathering  The debris thus created often transported by erosional processes via streams, glaciers, wind, and gravity  When this debris is deposited as permanent sediment, the processes of burial, compression, and chemical alteration over long periods of time produce sedimentary rocks  Geologic processes like tectonic folding and faulting exert heat and pressure on both igneous and sedimentary rocks, altering them physically or chemically – rocks modified in this way are termed metamorphic rocks  Any of the rock types can eventually be returned to Earth's interior by tectonic forces at areas known as subduction zones  Once in Earth's interior, extreme pressures and temperatures melt the rock back into magma to begin the rock cycle again  Driving mechanisms of the rock cycle Earth is a dynamic planet with the surface and interior in a constant state of flux. – Internal changes alter the surface by moving the Earth’s plates, building mountains. – Seas advance and retreat over the continents brining in new materials and taking other materials away. – Rocks are continually being changed by Earth’s forces.  A schematic diagram of the rock cycle concept, which states that geologic processes act continuously to produce new rocks from old ones. END