Rocks And Minerals PDF

SECTION-II ROCKS AND MINERALS Dr Navdeep Singh Assistant Professor DEPARTMENT OF CIVIL ENGINEERING Dr B R AMBEDKAR NATIONAL INSTITUTE OF TECHNOLOGY JALANDHAR, INDIA...

SECTION-II ROCKS AND MINERALS Dr Navdeep Singh Assistant Professor DEPARTMENT OF CIVIL ENGINEERING Dr B R AMBEDKAR NATIONAL INSTITUTE OF TECHNOLOGY JALANDHAR, INDIA 1  CONTENT Rocks and Minerals Minerals, their identification and physical properties of minerals, igneous, sedimentary and metamorphic rocks, their formation and structures. Classification of rocks for engineering purposes. Rock quality designation (RQD). 2  WHAT ARE MINERALS? Minerals are formed through geological processes, such as magmatic activity, metamorphism, and sedimentation. They can be found in rocks, soil, water, and even in our daily lives. Minerals have a unique combination of chemical composition and crystal structure that distinguishes them from other natural substances. IDENTIFICATION OF MINERALS To identify a mineral, you need to examine its physical and chemical properties. Here are some common methods: Appearance: Observe the mineral's color, shape, size, and texture. Hardness: the Mohs hardness scale (1-10) to determine the mineral's scratch resistance. Streak: Scratch the mineral on a porcelain plate to see the color of the powder produced (streak). Cleavage: Examine the mineral's breakage pattern (e.g., conchoidal, splintery, or uneven). Density: Measure the mineral's density using a densitometer. Optical properties: Use a polarizing microscope to examine the mineral's optical properties, such as refractive index and birefringence. 3 MINERALS 4  IDENTIFICATION OF MINERALS MOHS HARDNESS SCALE The Mohs hardness scale is a qualitative scale that characterizes the scratch resistance of various minerals through the ability of harder materials to scratch softer ones. The scale was created by Friedrich Mohs in 1812 and consists of ten standard minerals, each assigned a relative hardness value from 1 to 10. Here are the minerals on the scale, listed from softest to hardest: Talc - Very soft, can be scratched with a fingernail. Gypsum - Can be scratched with a fingernail, but harder than talc. Calcite - Can be scratched with a copper coin. Fluorite - Can be scratched with a nail (hardness ~4). Apatite - Can be scratched with a knife (hardness ~5). Orthoclase Feldspar - Can be scratched with a steel file (hardness ~6). Quartz - Can scratch glass (hardness ~7). Topaz - Harder than quartz and can scratch it (hardness ~8). Corundum - Includes sapphire and ruby; very hard (hardness ~9). Diamond - The hardest naturally occurring material (hardness ~10). 5 6  IDENTIFICATION OF MINERALS STREAK Streak refer to the color of the powdered form of a mineral, which can be determined by rubbing the mineral on a hard surface, typically a piece of unglazed porcelain called a streak plate. The streak can provide valuable information for mineral identification, as it may differ from the color of the mineral in its solid form. Key Points about Streak: Diagnostic Property: Streak is often more reliable than the external color of the mineral, as some minerals can appear in various colors due to impurities. Testing Method: To perform a streak test, you simply scratch the mineral across the streak plate and observe the color of the resulting powder. Variability: Some minerals, like hematite, may have a metallic luster in their solid form but leave a reddish-brown streak. Minerals with Colorless Streaks: Some minerals may produce a colorless or white streak regardless of their external color. Importance in Identification: Using streak in combination with other physical properties like hardness, luster, and cleavage can help in accurately identifying minerals. 7 IDENTIFICATION OF MINERALS STREAK 8  IDENTIFICATION OF MINERALS CLEAVAGE Cleavage in mineralogy refers to a mineral's ability to break along specific planes of weakness in its crystal structure. This characteristic is important for identifying minerals. When a mineral exhibits cleavage, it breaks cleanly along these planes, producing smooth surfaces. Minerals are classified based on their cleavage characteristics, which can include: Number of Cleavage Directions: One Direction: Mica exhibits perfect cleavage in one direction, allowing it to peel into thin sheets. Two Directions: Feldspar minerals often show two directions of cleavage that intersect at approximately 90 degrees. Three Directions: Halite displays three cleavage directions, intersecting at right angles, resulting in cubic fragments. Four Directions: Some minerals, like fluorite, can exhibit four directions of cleavage. Quality of Cleavage: Perfect: Forms very smooth surfaces. Good: Still forms smooth surfaces but may not be as perfect. Poor: Cleavage planes are less distinct. Cleavage Angles: The angles between the cleavage planes can also be measured, which can aid in identification. 9 IDENTIFICATION OF MINERALS CLEAVAGE 10  IDENTIFICATION OF MINERALS OPTICAL PROPERTIES The optical properties of minerals are critical for understanding their identification, characterization, and behavior under various conditions, especially in fields like geology, materials science, and mineralogy. The key optical properties of minerals include: Birefringence: Some minerals exhibit double refraction, where light is split into two rays when passing through. This property is especially important in the study of anisotropic minerals using polarized light microscopy. Birefringence can be quantified as the difference in the refractive indices of a mineral. Refractive Index: This measures the bending of light as it passes through a mineral. Different minerals have characteristic refractive indices, which can be used for identification. Pleochroism: Some minerals display different colors when viewed from different angles under polarized light. This property is particularly significant in the identification of certain gemstones and other colored minerals. Fluorescence and Phosphorescence: Certain minerals can emit light of a different wavelength when exposed to ultraviolet light (fluorescence) or continue to glow even after the light source has been removed (phosphorescence). Absorption Spectrum: The specific wavelengths of light absorbed by a mineral can provide clues about its composition and can be measured using spectroscopic techniques. Optical Relief: This describes how distinct the boundaries are when viewed under a microscope, which can vary depending on the difference in refractive indices between the mineral and its mounting medium. 11 IDENTIFICATION OF MINERALS OPTICAL PROPERTIES 12  PHYSICAL PROPERTIES OF MINERALS Minerals exhibit various physical properties that can be used for identification. Here are some common ones: Luster: The way light interacts with the mineral's surface (e.g., metallic, glassy, earthy, or pearly). Diaphaneity: Whether the mineral is transparent, translucent, or opaque. Crystal system: The arrangement of atoms within the mineral's crystal structure (e.g., cubic, hexagonal, or monoclinic). Habit: The shape of the mineral crystals (e.g., tabular, prismatic, or fibrous). Fracture: The way the mineral breaks when struck (e.g., conchoidal, uneven, or fibrous). Tenacity: The mineral's resistance to scratching and wear. 13  PHYSICAL PROPERTIES OF MINERALS LUSTER Luster is a property of minerals that describes how they reflect light from their surfaces. It is an important characteristic for mineral identification and helps distinguish between minerals with similar colors or appearances. Luster is categorized based on the quality and appearance of the reflection. Here are the main types of luster: Metallic: Minerals with a metallic luster shine like polished metal. They have a reflective surface that resembles metals such as gold, silver, or copper. Examples include pyrite (fool's gold) and galena. Non-Metallic: Non-metallic luster includes a variety of appearances that do not resemble metals. It can be further classified into several subtypes: Vitreous: Also known as glassy luster, it resembles the shine of glass. Examples include quartz and fluorite. Pearly: This luster has a soft, iridescent sheen similar to the surface of a pearl. Examples include mica and talc. Silky: Minerals with a silky luster have a sheen similar to silk fabric, often due to fine fibrous structures. Examples include asbestos and satin spar gypsum. Resinous: This luster is akin to the appearance of resins or plastics, giving a somewhat greasy or glossy appearance. Examples include amber and sphalerite. Adamantine: This luster is very bright and diamond-like, providing an intense sparkle. Examples include diamonds and zircon. Earthy: Earthy luster is dull and matte, resembling the appearance of clay or soil. Examples include kaolinite and limonite. 14 PHYSICAL PROPERTIES OF MINERALS LUSTER 15  PHYSICAL PROPERTIES OF MINERALS DIAPHANEITY Diaphaneity refers to the transparency or translucency of a mineral, indicating how much light can pass through it. Minerals can generally be classified into three categories based on their diaphaneity: Transparent Minerals: These minerals allow light to pass through clearly, and objects can be seen clearly through them. Examples include: Quartz Feldspar Diamond Translucent Minerals: These minerals allow some light to pass through but not enough to see objects clearly. Examples include: Calcite Agate Opal Opaque Minerals: These minerals do not allow light to pass through at all. Examples include: Hematite Pyrite Galena 16  PHYSICAL PROPERTIES OF MINERALS CRYSTAL SYSTEMS Minerals can be classified into different crystal systems based on their crystal lattice structure. The seven primary crystal systems are: Cubic (Isometric): Characterized by three axes of equal length intersecting at 90 degrees. Examples - Halite (NaCl) ,Diamond Tetragonal: Similar to cubic, but with one axis longer or shorter than the other two, which are the same length. Examples include: Zircon (ZrSiO4) Rutile (TiO2) Orthorhombic: Features three unequal axes that intersect at 90 degrees. Examples include: Barite (BaSO4) ,Topaz (Al2SiO4(F,OH)2) Hexagonal: Contains four axes, with three of equal length that are oriented at 120 degrees to each other, and a fourth axis of a different length perpendicular to the others. Examples include: Quartz (SiO2), Beryl (Be3Al2Si6O18) Trigonal: Often considered part of the hexagonal system, characterized by three equal axes in a plane at 120 degrees to each other, and a vertical axis of unequal length. Examples include: Calcite (CaCO3), Tourmaline Monoclinic: Includes three unequal axes, with two axes intersecting at an angle that is not 90 degrees and the third axis perpendicular to the plane formed by the other two. Examples include: Gypsum (CaSO4·2H2O) Mica (such as Biotite) Triclinic: Contains three unequal axes, with all axes intersecting at angles that are not 90 degrees. Examples include: Plagioclase Feldspar, Turquoise (CuAl6(PO4)4(OH)8·4H2O) 17 PHYSICAL PROPERTIES OF MINERALS CRYSTAL SYSTEMS 18 PHYSICAL PROPERTIES OF MINERALS CRYSTAL SYSTEMS 19  PHYSICAL PROPERTIES OF MINERALS HABIT Crystal habit describes the physical form or appearance of a crystal or an aggregate of crystals as it grows in nature. The term encompasses various aspects including the shape, size, and arrangement of the crystals. Some common crystal habits include: Prismatic: Crystals that are elongated with flat surfaces, like quartz. Cubical: Crystals that form cubes, such as those found in halite (rock salt). Tabular: Flat, plate-like crystals that resemble a tablet. Dendritic: Branching patterns that resemble tree-like structures. Acicular: Needle-like crystals that are typically long and slender. Fibrous: Crystals that form fine threads or fibers, such as asbestos. Massive: Aggregates of crystals that do not show any clear external crystal faces. Different minerals can exhibit a wide variety of crystal habits depending on their chemical composition and the conditions under which they formed. For example, quartz can appear in prismatic, massive, or even fibrous forms depending on its environmental conditions 20 PHYSICAL PROPERTIES OF MINERALS HABIT 21 PHYSICAL PROPERTIES OF MINERALS HABIT 22  PHYSICAL PROPERTIES OF MINERALS FRACTURE The fracture property of minerals describes how a mineral breaks when it is subjected to stress, as opposed to cleavage, which refers to how a mineral splits along its natural planes of weakness. Fracture is important in identifying minerals because it provides insight into their internal structure and bonding. There are several types of fracture patterns: Conchoidal Fracture: This type produces smooth, curved surfaces that resemble the shape of a seashell. It's common in minerals like quartz and obsidian. Conchoidal fracture often occurs when there is no distinct plane of weakness in the mineral’s crystal structure. Uneven Fracture: This produces rough, irregular surfaces. The mineral breaks in a jagged and non-uniform manner. This type is common in minerals like feldspar. Hackly Fracture: Characterized by sharp, jagged edges and surfaces, hackly fracture is often seen in metals like native copper. It looks as though the mineral has been torn apart. Fibrous Fracture: This type results in a surface that looks like fibers or threads. It is commonly observed in minerals like asbestos. Splintery Fracture: This type produces long, splinter-like fragments. It often occurs in minerals with fibrous or elongated crystals 23 PHYSICAL PROPERTIES OF MINERALS FRACTURE 24  PHYSICAL PROPERTIES OF MINERALS TENACITY Tenacity in minerals refers to a mineral's resistance to deformation, breaking, or changing shape when subjected to physical forces. It's an important property for understanding how minerals will behave under stress, and it helps distinguish between minerals with similar physical appearances. There are several types of tenacity: Brittle: Minerals that are brittle break or shatter easily when subjected to stress. They tend to fracture rather than bend or deform. Examples include quartz and calcite. Malleable: Malleable minerals can be hammered or rolled into thin sheets without breaking. This property is characteristic of metals, like gold and silver. Ductile: Ductile minerals can be drawn into wires without breaking. This is also typical of metals. For instance, copper is a ductile mineral. Flexible: Flexible minerals bend when stressed but return to their original shape when the stress is removed. This property is seen in minerals like talc. Elastic: Elastic minerals can be bent and return to their original shape once the stress is removed. An example is mica, which can bend and then snap back to its original form. Sectile: Sectile minerals can be cut or sliced with a knife into thin shavings. This property is observed in minerals like gypsum. 25 PHYSICAL PROPERTIES OF MINERALS TENACITY 26 SOME COMMON MINERALS AND THEIR PHYSICAL PROPERTIES Quartz (SiO2): Calcite (CaCO3): Pyrite (FeS2): Hardness: 7 Hardness: 3 Hardness: 6-6.5 Streak: White Streak: White Streak: Brassy yellow Cleavage: Conchoidal Cleavage: Rhombohedral Cleavage: Octahedral Luster: Vitreous Luster: Vitreous Luster: Metallic 27 ROCK CYCLE 28 ROCK CYCLE 29  IGNEOUS ROCKS Igneous rocks are formed from the cooling and solidification of magma (molten rock) from the Earth's interior. They can be further divided into two categories: Granite Gabbro Basalt Obsidian Intrusive Igneous Rocks: Formed below the Earth's Extrusive Igneous Rocks: Formed above the surface, these rocks cool and solidify slowly, Earth's surface, these rocks cool and solidify quickly, resulting in larger crystals and a coarse-grained resulting in smaller crystals and a fine-grained texture. Examples include granite and gabbro. texture. Examples include basalt and obsidian. 30  CHARACTERISTICS OF IGNEOUS ROCKS Coarse-grained or fine-grained texture Can be glassy or crystalline Often have a glassy or shiny appearance Can contain phenocrysts (large crystals that form during slow cooling) Can be highly variable in composition IGNEOUS ROCKS FORMATION Magma Generation: Magma is formed when the Earth's mantle partially melts due to heat, pressure, or the introduction of water. Ascent: Magma rises through the crust, driven by buoyancy and pressure. Emplacement: Magma cools and solidifies at the surface or within the Earth's crust. STRUCTURES Texture: Igneous rocks can have a range of textures, including: Aphanitic (fine-grained): Basalt, obsidian Phaneritic (coarse-grained): Granite, gabbro Glassy: Obsidian, pumice Mineral Composition: Igneous rocks are primarily composed of silicates (quartz, feldspar, mica), oxides (iron, titanium), and other minerals. 31  FORMATION OF IGNEOUS ROCKS Formation of igneous rocks involves the cooling and solidification of molten rock material, which can occur in various geological settings. The processes involved in the formation of igneous rocks: 1. Magma Formation Source: Magma forms from the melting of pre-existing rock in the Earth's mantle or lower crust due to factors such as increased temperature, decreased pressure, or the addition of volatiles (e.g., water). Composition: Magma is a complex mixture of molten rock, crystals, and dissolved gases. Its composition can vary widely, influencing the types of igneous rocks that will form. 2. Intrusive Igneous Rocks (Plutonic Rocks) Formation: Intrusive igneous rocks form when magma cools and solidifies below the Earth’s surface. The magma cools slowly, allowing large crystals to form. Cooling Process: The cooling rate is slow because the magma is insulated by surrounding rock, which leads to the formation of coarse-grained textures. 32  FORMATION OF IGNEOUS ROCKS 3. Extrusive Igneous Rocks (Volcanic Rocks) Formation: Extrusive igneous rocks form when magma reaches the Earth’s surface and erupts as lava. Upon eruption, the lava cools quickly. Cooling Process: Rapid cooling at or near the surface results in fine-grained textures, with smaller crystals or a glassy appearance. 4. Volcanic Eruptions and Lava Types Effusive Eruptions: Involve the gentle flow of lava that solidifies into basalt or andesite. The lava flow can create expansive lava fields or shield volcanoes. Explosive Eruptions: Involve the violent ejection of magma and gases, which can produce pyroclastic materials such as ash, pumice, and volcanic bombs. The lava that cools quickly in these eruptions can form rocks with a glassy or vesicular texture. 5. Factors Influencing Rock Type Temperature: Higher temperatures lead to the melting of rock, while the cooling temperature determines crystal size and rock texture. Pressure: Higher pressures generally lead to the formation of magma that cools slowly, resulting in intrusive rocks. Volatiles: The presence of gases and other volatiles in magma affects its viscosity and eruption style, influencing the types of igneous rocks formed 33 FORMATION OF IGNEOUS ROCKS 34  SEDIMENTARY ROCKS Sedimentary rocks are formed from the accumulation and compression of mineral or organic particles, such as sand, silt, or clay. These particles can come from a variety of sources, including: Clastic Sedimentary Rocks: Chemical Sedimentary Rocks: Organic Sedimentary Rocks: Formed from the erosion and Formed through chemical Formed from the accumulation weathering of pre-existing rocks. precipitation from solution. of plant or animal remains. 35  CHARACTERISTICS OF SEDIMENTARY ROCKS Layered or stratified structure Composed of grains or particles Can be porous or non-porous May contain fossils Can be cemented together by minerals STRUCTURES Layering: Sedimentary rocks often exhibit layering or stratification due to changes in sediment supply or environmental conditions. Foliation: Sedimentary rocks can exhibit foliation, where minerals align parallel to each other due to pressure and temperature changes. Cementation: Minerals precipitate out of solution and bind particles together, forming a cohesive rock 36  SEDIMENTARY ROCKS FORMATION Sedimentary rocks form from the accumulation and lithification of sediments. These sediments can originate from the weathering and erosion of pre-existing rocks (igneous, metamorphic, or sedimentary), or from biological processes. The formation of sedimentary rocks involves several key stages: weathering, erosion, transportation, deposition, and lithification. Weathering Physical Weathering: Breakdown of rocks into smaller pieces due to physical forces such as freeze-thaw cycles, thermal expansion, or abrasion. This process results in the production of clasts (rock fragments). Chemical Weathering: Alteration of minerals in rocks through chemical reactions, such as oxidation, hydrolysis, or dissolution. This process can produce new minerals and soluble ions that contribute to sediment formation. Biological Weathering: Involves the actions of organisms, such as plant roots breaking rocks or lichens producing acids that dissolve minerals. This also contributes to the formation of sediments. Erosion The process of removing weathered material from its original location by agents such as water, wind, ice, or gravity. Erosion transports sediments away from their source. 37  SEDIMENTARY ROCKS FORMATION Transportation Agents of Transportation: Sediments are carried by natural forces like rivers, wind, glaciers, and ocean currents. The method of transportation affects the size and sorting of sediments. Sediment Sorting: During transportation, sediments are sorted by size and density. Larger, heavier particles settle out first, while finer particles are carried farther. Deposition Deposition: Occurs when the transporting agents lose energy and can no longer carry sediments, causing them to settle. Deposition can occur in various environments such as riverbeds, lake bottoms, deserts, or ocean floors. Depositional Environments: Continental: Includes rivers, lakes, and deserts. Sediments in these environments are often well-sorted. Marine: Includes beaches, deltas, and deep-sea environments. Marine sediments can vary greatly in size and composition. Transitional: Includes estuaries and tidal flats where freshwater and saltwater mix. 38  SEDIMENTARY ROCKS FORMATION Lithification Compaction: The process of squeezing out water from sediment layers due to the weight of overlying sediments. As sediments are buried deeper, the pressure increases, causing the grains to pack more tightly. Cementation: The process where minerals precipitate from groundwater and fill the spaces between sediment grains, binding them together into a solid rock. Common cementing agents include silica, calcium carbonate, and iron oxides. Recrystallization: In some cases, minerals in the sediments may recrystallize during lithification, further strengthening the rock. Sedimentary Structures Stratification: Layers of sedimentary rock, which reflect changes in sediment deposition over time. Fossils: Remains of ancient organisms preserved in sedimentary rocks, providing information about past environments and life forms. Ripple Marks and Mud-cracks: Structures that indicate the conditions of sediment deposition, such as water movement or alternating wet and dry conditions. 39 SEDIMENTARY ROCKS FORMATION 40 SEDIMENTARY ROCKS FORMATION 41  METAMORPHIC ROCKS Metamorphic rocks are formed when existing rocks are transformed by heat, pressure, and chemical reactions. This process can occur due to tectonic forces, contact metamorphism (heat from magma), or hydrothermal activity. Marble Slate Quartzite (metamorphosed limestone) (metamorphosed shale) (metamorphosed sandstone) 42  TYPES OF METAMORPHIC ROCKS Foliated Metamorphic Rocks: Definition: Rocks with a layered or banded appearance due to the alignment of platy minerals under directed pressure. Examples: Slate: Forms from the low-grade metamorphism of shale; has a fine-grained texture and splits into thin, flat layers. Schist: Forms from intermediate to high-grade metamorphism of shale or volcanic rocks; contains larger, visible crystals of minerals like mica or garnet. Gneiss: Forms from high-grade metamorphism of granite or volcanic rocks; exhibits pronounced banding or layering of light and dark minerals. Non-Foliated Metamorphic Rocks: Definition: Rocks that do not exhibit layering or banding. They typically form where pressure is not directed or the original rock was non-foliated. Examples: Marble: Forms from the metamorphism of limestone or dolostone; composed mainly of recrystallized calcite or dolomite. Quartzite: Forms from the metamorphism of quartz-rich sandstone; consists mainly of fused quartz grains. 43 44  CHARACTERISTICS OF METAMORPHIC ROCKS Altered mineral composition Recrystallized minerals with new textures Foliation (layering) or lineation (banding) Can exhibit replacement of minerals May contain evidence of deformation (folding, faulting) STRUCTURES Foliation: Metamorphic rocks often exhibit foliation, where minerals align parallel to each other due to pressure and temperature changes. Lineation: Metamorphic rocks can exhibit lineation, where minerals align perpendicular to the direction of tectonic forces. Mineral Replacement: Minerals are replaced or altered due to changes in temperature and pressure. 45  METAMORPHIC ROCKS FORMATION Tectonic Forces: Tectonic forces cause rocks to be subjected to high pressure and temperature changes. Deformation: Rocks are deformed through folding, faulting, or other mechanisms. Metamorphism - Metamorphism is the process by which existing rocks (igneous, sedimentary, or other metamorphic rocks) are altered into metamorphic rocks due to changes in environmental conditions. The key factors driving metamorphism are: Temperature: Elevated temperatures can cause minerals in the parent rock to recrystallize into new minerals that are stable at higher temperatures. Pressure: Increased pressure, often due to burial beneath other rocks or tectonic forces, can cause minerals to recrystallize or reorganize, leading to denser rocks. Chemically Active Fluids: Fluids, such as water with dissolved ions, can facilitate the movement of ions and promote the formation of new minerals through chemical reactions. 46 METAMORPHIC ROCKS FORMATION 47  TYPES OF METAMORPHISM Contact Metamorphism: Occurs: When rocks are heated by proximity to molten magma or lava. Characteristics: Typically results in localized metamorphism in the surrounding rock, creating a metamorphic aureole around the intrusion. The heat from the magma causes recrystallization of minerals in the surrounding rock. Example: Marble forms from the metamorphism of limestone, and quartzite forms from sandstone. Regional Metamorphism: Occurs: Over large areas under conditions of high pressure and temperature, usually associated with tectonic plate collisions and mountain-building processes. Characteristics: Results in significant metamorphic changes over extensive areas, leading to the formation of foliated rocks. High pressure and temperature cause minerals to realign or recrystallize. Example: Schist forms from shale, and gneiss forms from granite. 48  TYPES OF METAMORPHISM Hydrothermal Metamorphism: Occurs: When rocks are altered by hot, chemically reactive fluids, usually associated with mid-ocean ridges or volcanic regions. Characteristics: Results in the introduction of new minerals from the circulating fluids, leading to changes in the mineral composition of the rock. Example: Serpentine forms from the alteration of ultramafic rocks like peridotite. Dynamic Metamorphism: Occurs: Due to high pressure and shear stress, often associated with fault zones where rocks are subjected to intense deformation. Characteristics: Produces rocks with a strong foliation or lineation due to the alignment of minerals under directed pressure. Example: Mylonite forms in fault zones where rocks are ground up and recrystallized. 49  FACTORS INFLUENCING METAMORPHISM 1. Temperature Drives recrystallization of minerals. Increases with depth or proximity to molten magma. Higher temperatures lead to more intense metamorphic changes. 2. Pressure Confining Pressure: Uniform pressure in all directions, increases rock density. Directed Pressure: Unequal pressure causes mineral alignment, leading to foliation or lineation. 3. Chemically Active Fluids Facilitate chemical reactions that alter mineral composition. Fluids introduce or remove elements, driving metasomatic changes. 4. Parent Rock (Protolith) Determines initial mineral composition and texture. Influences the types of minerals and textures that develop during metamorphism. 50  FACTORS INFLUENCING METAMORPHISM 5. Time Longer exposure to metamorphic conditions leads to more pronounced changes. Affects the extent of recrystallization and development of textures. 6. Tectonic Activity Creates conditions of high pressure and temperature. Influences the scale and orientation of metamorphic changes. 7. Geothermal Gradient The rate of temperature increase with depth. Determines whether metamorphism will be low-grade or high-grade. 8. Metamorphic Facies Classification of mineral assemblages formed under specific pressure and temperature conditions. Helps interpret metamorphic environments and conditions 51 CLASSIFICATION OF ROCKS FOR ENGINEERING PURPOSES Based on engineering properties: Strength: the ability of a rock to resist deformation or breakage under load. Deformation Modulus: the ratio of stress to strain (deformation) in a rock. Poisson's Ratio: the ratio of lateral strain to longitudinal strain. Density: the mass per unit volume of the rock. Porosity: the percentage of void space within the rock. Igneous Rocks Granite: coarse-grained, resistant to weathering, high strength Basalt: fine-grained, prone to weathering, moderate strength Gabbro: coarse-grained, resistant to weathering, high strength Volcanic Rock: fine-grained, porous, low to moderate strength Sedimentary Rocks Sandstone: well-sorted sand grains, porous, low to moderate strength Shale: fine-grained, platy structure, high compressive strength Conglomerate: coarse-grained, poorly sorted, high strength Limestone: calcium carbonate-rich, porous, moderate strength Marl: a type of limestone with a high clay content Metamorphic Rocks Marble: recrystallized limestone, metamorphic texture, low to moderate strength Slate: metamorphosed shale, platy structure, high compressive strength Schist: metamorphosed sedimentary rock, foliated texture, high strength Gneiss: metamorphosed igneous or sedimentary rock, banded texture, high strength 52  Rock Quality Designation (RQD) IS 11315 (Part 11) : 2023 Methods For Quantitative Description Of Discontinuities In Rock Masses – Part 11 Core Recovery And Rock Quality Designation Rock Quality Designation (RQD) is a method used to assess the quality of rock cores or samples extracted from the ground. It is a widely used technique in geotechnical engineering and mining industries to evaluate the degree of fragmentation, weathering, and discontinuities in rocks. Definition: RQD is a numerical value that represents the percentage of rock core recovered during drilling or coring, where: RQD = (Total length of intact rock core more than 10 cm long / Total length of core run) x 100 Interpretation: RQD values range from 0 to 100, with higher values indicating better rock quality and lower values indicating poorer rock quality. The following are general guidelines for interpreting RQD values: The RQD system assigns a rating from 0 to 100% based on the percentage of intact rock fragments (>2 cm in diameter) recovered from a sample. The rating is calculated as follows: Measure the length of each sample (e.g., core or channel sample). Count the number of pieces of rock that are >2 cm in diameter. It is a simple process which involves counting up the pieces of drill core which are more than 10 cm long and fully intact. Calculate the percentage of intact rock fragments by dividing the number of pieces by the total length of the sample. Multiply this percentage by 100 to get the RQD value (0-100%). 53 Example 54 RQD values can be categorized into five classes: Excellent (RQD >90%): High-quality rock with minimal fragmentation and few discontinuities. Good (RQD 75-90%): Rock with moderate fragmentation and some discontinuities. Fair (RQD 50-75 %): Rock with significant fragmentation and many discontinuities. Poor (RQD 25-50%): Rock with severe fragmentation and numerous large discontinuities. Very Poor (RQD