Properties of Rocks PDF

Properties of Rocks Petrology is the study of rocks - igneous, metamorphic, and sedimentary - and the processes that form and transform them.  A rock is a naturally occurring aggregate of minerals or other rock fragments. Classified by their origin, composition, and texture. Physical Properties...

Properties of Rocks Petrology is the study of rocks - igneous, metamorphic, and sedimentary - and the processes that form and transform them.  A rock is a naturally occurring aggregate of minerals or other rock fragments. Classified by their origin, composition, and texture. Physical Properties of Rocks Common properties of rocks THREE MAIN CATEGORIES OF ROCKS There are three types of rocks: igneous, sedimentary and metamorphic. Each of these types is part of the rock cycle. Through changes in conditions one rock type can become another rock type.  Igneous Rocks Igneous rocks are “fire- born,” meaning that they are formed from the cooling and solidification of molten (melted) rock. The word igneous derives from ignis, the Latin word for “fire.” Molten rock material is known as magma until it is erupted onto the surface when it then is termed lava.  Composition and Minerals in Igneous Rocks Igneous rocks are mostly made of the most common elements found in the Earth’s crust. In descending order, they are: Oxygen (0) Silicon (Si) Aluminum (Al) Iron (Fe) Calcium (Ca) Sodium (Na) Magnesium (Mg) Potassium (K) Almost all igneous rocks are silicates meaning that silicon and oxygen are the two most common elements in them. The two major divisions of igneous rocks based on composition are: Mafic - high in magnesium and iron (and low in silica) Silicic - high in silica (and low in magnesium and iron)  Intrusive (Plutonic) Rocks Extrusive (Volcanic) Rocks Formed from magma that cools Formed on the surface of and solidifies within the crust of the Earth from lava, which the Earth. is magma that has emerged Intrusive igneous rocks are generally wholly crystalline and from underground. characterized by large crystal Volcanic rocks have sizes visible to the naked eye generally smaller crystal because they cool slowly. size and usually have a They have large crystals very-fine-grained or glassy because it cool slowly without groundmass that formed ever reaching the surface. due to rapid cooling at the time of eruption.  EXAMPLES OF IGNEOUS ROCKS Granite is a light-colored, coarse-grained igneous rock that is formed from slowly cooling magma deep within the Earth. It is the most common intrusive igneous rock and is often found in large masses called batholiths. Granite is composed primarily of quartz, feldspar, and mica. Gabbro is a dark-colored, coarse-grained igneous rock that is also formed from slowly cooling magma. It is the most common intrusive igneous rock after granite and is often found in large masses called plutons. Gabbro is composed primarily of plagioclase feldspar and olivine. The plagioclase feldspar crystals give gabbro its dark color, while the olivine crystals contribute to its hardness. Pegmatite is an extremely coarse-grained igneous rock that is formed from very slowly cooling magma. It is often found in veins and dikes, which are thin, tabular bodies of rock that intrude into existing rock. Pegmatite is composed of a wide variety of minerals, including quartz, feldspar, mica, and gemstones such as tourmaline and beryl. Basalt is a dark-colored, fine-grained igneous rock that is formed from rapidly cooling lava on the surface of the Earth or beneath the surface of the ocean. It is the most common extrusive igneous rock and is often found in layers called flows. Basalt is composed primarily of plagioclase feldspar and pyroxene. Andesite is a gray-colored, fine-grained igneous rock that is formed from intermediate-composition lava. It is the second most common extrusive igneous rock and is often found in layers called flows. Andesite is composed primarily of plagioclase feldspar, amphibole, and pyroxene. Rhyolite is a light-colored, fine-grained igneous rock that is formed from rapidly cooling lava on the surface of the Earth or beneath the surface of the ocean. It is the third most common extrusive igneous rock and is often found in layers called flows. Rhyolite is composed primarily of quartz and feldspar. The quartz crystals give rhyolite its light color, while the feldspar crystals contribute to its strength and durability.  Sedimentary rocks These rocks often start as sediments carried in rivers and deposited in lakes and oceans. When buried, the sediments lose water and become cemented to form rock. Sedimentary rocks are formed from pre-existing rocks or pieces of once- living organisms. They form from deposits that accumulate on the Earth's surface. Sedimentary rocks often have distinctive layering or bedding.  Sedimentary rocks form by the compaction and cementing together of sediments, broken pieces of rock- like gravel, sand, silt, or clay. It also includes chemical precipitates, the solid materials left Breccia behind after a liquid evaporates. The most important geological processes that lead to the creation of sedimentary rocks are erosion, weathering, dissolution, precipitation, and lithification. Coal  Types of Sedimentary Rocks The sedimentary rocks are classified into three different types: Organic, Clastic and Chemical Sedimentary Rocks.  Organic Sedimentary Rocks form from the accumulation of plant or animal debris. Examples include: chalk, coal, diatomite, some dolomites, and some limestones. Chalk Coal Diatomite Dolomite Limestones  Clastic sedimentary rocks form from the accumulation and lithification of mechanical weathering debris. Examples: breccia, conglomerate, sandstone, silts tone, and shale.  Chemical sedimentary rocks form when dissolved materials precipitate from solution. Examples include: chert, some dolomites, flint, iron ore, limestones, and rock salt. The Principle of Superposition This principle states that layers of rock are superimposed, or laid down one on top of another. The oldest rock strata will be on the bottom and the youngest at the top. EXAMPLES OF SEDIMENTARY ROCKS  Metamorphic rocks Metamorphic rocks are type of rock that formed when pre-existing rocks (parent rocks) undergo significant physical or chemical changes under high pressure and temperature, without melting completely. This process, known as metamorphism, alters the texture, mineralogy, and composition of the original rock, creating a new rock type. Metamorphism, Literally Means "Change of Form."  Metamorphic source rocks, the rocks that experience the metamorphism, are called the parent rock or protolith, from proto– meaning first, and lithos- meaning rock.  Factors Influencing Metamorphism Temperature: Typically exceeding 150-200°C, elevated temperatures activate chemical reactions that alter the mineral composition of the parent rock. Pressure: Often greater than 100 megapascals, pressure compacts the rock, promoting recrystallization and the formation of new structures. Chemical Modifiers: Hot fluids carrying dissolved minerals can introduce new chemical components or remove existing ones, further modifying the rock's composition. Time: These transformative processes occur over vast timescales, spanning millions of years, allowing for gradual and profound changes.  How Are Metamorphic Rocks Formed? Metamorphism can occur through various processes, including: A. Regional Metamorphism is the dominant process, responsible for the formation of vast areas of metamorphic rock. It occurs due to immense pressure and heat generated during: Mountain Building: As tectonic plates collide, immense forces compress and uplift rock layers, subjecting them to high pressure and shearing forces. Continental Collisions: When continents collide, the immense pressure and heat generated can lead to extensive regional metamorphism.  Subduction Zones: When oceanic plates subduct beneath continental plates, the descending plate undvarious metamorphic rocks. The ergoes intense heating and pressure, resulting in various metamorphic rocks. The intense heat and pressure of regional metamorphism trigger recrystallization of minerals in the parent rock, often creating the characteristic foliated textures.  B. Contact Metamorphism Occurs when a hot igneous intrusion comes into contact with surrounding cooler rocks. The heat from the intrusion bakes the surrounding rock, leading to its partial melting and recrystallization. This process typically results in non- foliated metamorphic rocks like marble and hornfels. The extent of contact metamorphism depends on the size and temperature of the intrusion, as well as the composition and permeability of the surrounding rock.  C. Hydrothermal Metamorphism Involves the interaction of hot, chemically-charged fluids circulating through rock formations. These fluids can dissolve existing minerals, precipitate new ones, and alter the overall texture and composition of the rock. Hydrothermal metamorphism is often associated with volcanic activity, geothermal areas, and near-surface mineral deposits. The specific type of hydrothermal metamorphism depends on the composition of the fluids and the temperature and pressure conditions.  Types of Metamorphic rocks A. Foliated Metamorphic Rocks ✓These rocks possess a layered or banded structure due to the alignment of platy minerals. ✓ This alignment is a result of the pressure and shearing forces they experience during metamorphism. Slate: This fine-grained rock, often grey or black, boasts a well-developed cleavage due to the alignment of aligned mica minerals that allows it to be split into thin sheets, commonly used for roofing and decorative purposes. Phyllite: Finely crystalline rock with a silky sheen and a more pronounced foliation than slate. It is sometimes used for decorative purposes. Schist: A coarse-grained rock with a well-developed foliation, schist is often composed of mica minerals that give it a flaky appearance. It is used in construction and for manufacturing electrical insulators. Gneiss: The most complex type of foliated rock, gneiss is often highly banded rock with alternating layers of light and dark minerals, sometimes containing augen (large, feldspar crystals). B. Non-foliated Metamorphic Rocks These rocks lack the layered structure and have a more homogenous appearance. The absence of foliation can be attributed to different factors like the composition of the parent rock and the type of metamorphism experienced. Examples of non-foliated metamorphic rocks include: Marble: A rock formed from recrystallized limestone composed primarily of calcite. It is also used in construction and for decorative purposes. Quartzite: A rock formed from recrystallized sandstone composed primarily of quartz. Quartzite is a very hard and durable rock. It is often used for countertops, flooring, and in construction. Hornfels: A fine-grained, non-foliated rock formed by contact metamorphism. Hornfels is often dark colored and has a fine-grained texture. It is used in construction and for paving. Novaculite: A hard, non-foliated, fine-grained rock formed from the metamorphism of chert. Novaculite used for whetstones and abrasives. Skarn: A non-foliated rock formed at the contact zone between igneous intrusions and carbonate rocks. Skarn is often rich in iron and other metals. It is used as a source of iron ore and other metals. Soapstone: Soapstone is a soft, non-foliated metamorphic rock composed mainly of talc. It is heat-resistant and easy to carve, making it suitable for fireplaces, countertops, and sculptures. Blue schist: A rare and beautiful rock formed under high pressure and low temperature conditions. Blue schist is characterized by its blue color due to the presence of the mineral glaucophane. Eclogite: Eclogite is a high-grade -high-pressure, high-temperature- metamorphic rock characterized by the presence of garnet and omphacite (a high-pressure pyroxene). These minerals indicate that the rock has undergone significant burial and compression within the Earth's crust or mantle. Eclogites often have a greenish-gray color and a coarse-grained, equigranular texture. Eclogite is important for understanding the processes that occur in the subduction zones. It is often found in association with diamond deposits. Migmatite: Migmatite A composite rock formed by the partial melting of a pre-existing rock, typically a gneiss or schist, followed by the intrusion of molten rock material (typically magma or fluid) into the partially melted rock. This results in a mixed rock with a distinct banding or patchy appearance. Serpentinite: A metamorphic rock composed primarily of serpentine minerals, often formed from ultramafic rocks. Is diamond a Rock or Mineral?  Diamonds are a rare occurrence on the surface of the planet because it takes extremely hot and high pressure conditions to create them. Diamond deposits around the world are associated with volcanic features called diatremes. A diatreme is a long, vertical pipe formed when gas-filled magma forces its way through the crust to explosively erupt at the surface. Kimberlite a special kind of intrusive igneous rock associated with some diatremes that sometimes contain diamonds, typical coarse grained an bluish in color.