GLY 108 – Plate Tectonics: The Active Earth Lab 3: Sedimentary Rocks Objectives: 1. Examine a rock and determine if it is igneous, metamorphic or sedimentary in origin. 2. Understand terms used to describe the textures of igneous, metamorphic & sedimentary rocks. 3. Be able to use and understand the classification scheme provided for each rock type and be able to recognize or name some of the more common rocks by sight. Introduction Last week we learned to identify some of the major rock-forming minerals. This week will build upon that extensive experience to understand better the rocks and their geologic significance. To an earth scientist, rocks represent much more than usable substances. They are the material of the earth understanding their origin and distribution helps us understand the earth and some of the major processes involved in changing the earth. It is often said (mostly by geologists) that “the history of the earth is written in the rocks” - we just have to be smart enough to read the "words." This week’s lab will allow you to investigate some of the common rocks that are found on and near the surface of the earth. The criteria used to classify igneous, sedimentary or metamorphic rocks will be examined, as well as the procedures in identifying rocks within each of these categories. Rocks... what are they?? For thousands of years rocks have proven their usefulness because of their durability and beauty. Granite and limestone are widely used as building materials and decorative coverings. Slate is utilized for hard, enduring table surfaces (such as pool tables) and fine marble have been used by sculptors for centuries to display their artistic talents. Rocks are mostly mixtures of one or more minerals and are classified into three main groups based on the processes that formed them. 1. Igneous Rocks: rocks formed from the cooling and solidification of magma or a lava. Magma: molten rock that forms naturally within the Earth. Magma may be either a liquid or a fluid mixture of liquid, crystals and dissolved gases. At the Earth's surface, magma is called lava. 2. Sedimentary Rocks: a rock formed by the consolidation (lithification) of sediments, it may consist of fragments and mineral grains of varying sizes from pre-existing rocks, the remains or products of animals and plants, or the or by precipitation of minerals from solution. 3. Metamorphic Rocks: igneous or sedimentary rocks that have been changed or altered by conditions of elevated temperature and/or pressure within the earth. THE ROCK The Rock Cycle: One of the most useful devices CYCLE for understanding rock types and the geologic processes that transform one rock type into another is the Rock Cycle. Through the course of time rocks are created, destroyed and altered through a set of internal and external processes operating on the earth. The rock cycle is an attempt to describe the series of events by which rocks are transformed from one type of rock to another over time. 1 ROCK IDENTIFICATION Texture and Composition When we identified minerals, we used the physical and chemical properties of the mineral. Rocks, however, are aggregates of one or more minerals. To recognize and identify the various rocks we will encounter in this course one must first be able to recognize the mineralogical composition of the rock and then the texture of the rock. 1. Composition refers to the minerals that are found in a rock. Often the larger mineral grains can be identified by sight or by using their physical properties. In some cases, small mineral grains may require the use of some magnifying device (microscope or hand lens) to assist in their identification. Occasionally, very small grains cannot be identified with the equipment that you have available - this is where practice and familiarity with the minerals will make your life much easier. 2. Texture refers to the shape, arrangement and size of mineral grains making up a rock. The shape and arrangement of mineral grains help determine the type of rock (e.g. igneous, metamorphic or sedimentary). Mineral grain size is then often used to classify rocks of a particular type. Each rock type uses different terms to describe textures... be sure to understand which terms are used for each rock type. Identification The first step in the identification of rocks is to determine the rock type. Each of the three rock types has a somewhat unique appearance that helps to distinguish one type from the other. This is often a lot harder than it sounds and you should rely on the talents and experience of your friendly instructor to help you learn this procedure. Table 1 gives some of the basic “Rules of Thumb” in identifying different rock types... look them over and become familiar with the characteristics associated with each. Table 1 Rules of Thumb Used in Identifying Different Rock Types IF THEN PROBABLY IT IS Rock shows a crystalline texture, that is, it seems to be made of random interlocking crystals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IGNEOUS Rock is glassy or comprised of many cavities or air holes (gas bubbles) . . . . . . . IGNEOUS Rock shows a clastic texture composed of randomly arranged mineral, rock and/or fossil fragments that are physically bound together . . . . . . . . . . . . . . SEDIMENTARY Rocks that are soft, or not very cohesive, they crumble apart easily into individual grains between one’s fingers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SEDIMENTARY Rocks that are visibly layered or have a tendency to break along bedding planes or contain fossils or fossil fragments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SEDIMENTARY Rock fizzes in acid, contains fossil fragments or is very fine grained. . . . . . . . . . SEDIMENTARY Rock fizzes in acid, consists of coarse interlocking crystals of equal size . . . . . . METAMORPHIC Rock contains crystals that are aligned or arranged so that they lie in same direction. These tend to contain abundant mica, garnets or amphibole. . . . . . . . . METAMORPHIC Rocks that are harder, denser of more compact, with a shiny or glittery appearance on broken surfaces. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . METAMORPHIC 2 LAB 3, SEDIMENTARY ROCKS Sedimentary Rock: rock formed from the weathered products of pre-existing rocks that have been transported, deposited and lithified. I. Detrital Sedimentary Rocks (Clastic Rocks): a sedimentary rock texture consisting of broken fragments of preexisting rock (classification is based on particle size and mineralogy of particles). A. Gravel: particle size is > 2 mm. 1. Breccia: a sedimentary rock composed of angular fragments of rock.. 2. Conglomerates: a sedimentary rock composed of rounded gravel sized rock fragments. B. Sand and Sandstones: particle size varies between 2 to 1/16 mm. 1. Quartz Sandstone: a sedimentary rock in which quartz is predominate detrital mineral. C. Mud and Mudstones: particle size is < 1/16 mm. Shale: a mudstone which shows the property of fissility = the tendency to break or split into thin layers. 1. Siltstone: a sedimentary rock in which particle size varies between 1/16 to 1/256 mm. 2. Claystone: a sedimentary rock in which particle size is < 1/256 mm. Lithification: the process by which an unconsolidated deposit of sediments is converted in to solid rock. Compaction, cementation and recrystallization are involved. A. Cementation: the precipitation of various mineral cements into the pore spaces of the rock. Most commonly calcite, quartz, clays, or iron compounds such as hematite or limonite. B. Compaction: the compression or packing together of sedimentary particles during burial. II. Chemical Sedimentary Rocks (Nonclastic Rocks): sedimentary rocks derived from material dissolved in water rather than discrete particles. Two types of Chemical Sedimentary Rocks. A. Inorganic: a sedimentary rock that precipitates directly from solution. 1. Evaporites: rocks that form by precipitation of crystals from the evaporation of water. a. Rock Gypsum: a massive or fine-grained variety of gypsum (CaSO4+2H2O). b. Rock Salt: a massive or fine-grained variety of halite (NaCl) generally derived from evaporation of seawater. 2. Chert: a dense hard sedimentary rock or mineral composed of microcrystalline quartz, SiO2. Unless colored by impurities chert is white, buff or light gray. Dark-colored varieties of chert are frequently referred to as flint, red varieties are called jasper. 3. Dolostone: a rock composed of the mineral dolomite, Ca,Mg(CO3)2. 4. Travertine: a deposit of limestone (calcite, CaCO3), which chemically precipitates from fresh waters around hot springs, rivers, lakes and cave deposits. B. Biochemical: rocks derived from the biological activity of plants and animals. 1. Limestone: a sedimentary rock composed predominantly of the mineral calcite, CaCO3. a. Fossiliferous Limestone: a limestone with abundant fossil remains. b. Coquina: a coarse grained limestone composed of loosely cemented shell fragments. c. Chalk: a finely textured, white, pure, marine limestone composed predominantly of calcareous shells of planktonic microorganisms such as coccolithophores and foraminifera. 2. Coal: initially forms in fresh water plant debris that accumulated swamps, bogs or marshes, under stagnant conditions. This plant material is then slowly converted to coal by increasing the temperature and pressure on this layer of organic material. Peat → Lignite → Bituminous Coal → Anthracite Coal (sedimentary rocks) ∫∫ (metamorphic rock) ─ burial temp., depth of burial, amount of fixed carbon, rank of coal increases → 3 IDENTIFICATION KEY FOR SEDIMENTARY ROCKS I. Clastic or Detrital Sedimentary Rocks: Grain Size > 2 mm 2 - 1/16 mm < 1/16 mm 1/16 - 1/256 mm < mm 1/256 Physical or Mineralogical Composition Other Properties and Comments Rock fragments Rock fragments Quartz Rounded fragments Angular fragments White, buff, red, brown color A variety of colors Fissile, any color Gritty texture, any color Smooth soft, light colored Quartz, mica, clay minerals Quartz, mica, clays Clay minerals Rock Name Conglomerate Breccia Quartz Sandstone Mudstone Shale Siltstone Claystone II. Chemical Sedimentary Rocks: Grain Size Composition Other Properties and Comments Rock Name Calcite (CaCO3) Occurs in bands or layers; white, buff, gray or black Variety of colors; fizzes in acid only when scratched Variety of colors, H = 7; (conchoidal fracture) White, gray, buff; H = 2; aggregate of gypsum crystals Salty taste; 3-D cleavage; aggregate of salt crystals Travertine A. Inorganic: Med. to coarse Reacts With crystalline Acid Fine to medium crystallline Fine to Does Not microcrystalline React Fine to coarsely With Acid crystalline Fine to coarsely crystallline B. Biochemical Dolomite (Ca,Mg(CO3)2) Quartz (SiO2) Gypsum (CaSO4*2H2O) Halite (NaCl) Reacts with Coarse to med. acid grained (Can be Coarse-grained scratched with nail) Fine-grained Contains fossil shell debris cemented by calcite Broken shell fragments loosely cemented by calcite Calcite, skeletons of pelagic microfossils (coccoliths, forams) Coarse-grained Plant remains, leaves, bark, Does Not and fibrous stems, roots react w/ acid Fine to medium Composed of finely brokenCarbonaceous grained Up plant fragments (organic-rich) Fine-grained Composed of finely comminuted plant fragments 4 Dolostone Chert (lt. colored) Flint (dark colored) Rock Gypsum Variety of colors Tan, buff to gray color Rock Salt Fossiliferous Limestone Coquina Soft; white or cream Chalk colored Soft; brown colored, Peat plant fibers Smudges fingers; dull Lignite luster; black - brown Black; dull-shiny; breaks Bituminous into rectangular pieces Coal Plate Tectonics Lab (GLY 108) Sedimentary Rock Identification Chart, Lab 3 Using the Identification Key for Sedimentary Rocks from the previous page, try to identify the following set of sedimentary rocks. Be sure to fill in the Identification Chart below as you identify the physical properties of each specimen. Clastic, Inorganic, or Biochemical Grain Size Mineralogical, Chemical (record size in mm if clastic) or Physical Composition Sedimentary Rock Name (crs, med, fine if nonclastic) 54 Sandstone 55 Fossil Limestone 56 Bituminous Coal 59 Chalk 61 Travertine 62 Conglomerate 63 Shale Questions: 1. How might you differentiate between limestone and basalt? 2. How does coal form? 3. What type of cement holds your sandstone sample together? 5 4. What type of cement, calcite or quartz, would make the best building stone? 5. How does chalk form? 6 GLY 108 – Plate Tectonics: The Active Earth Lab 2: Igneous Rocks Objectives: 1. Examine a rock and determine if it is igneous, metamorphic or sedimentary in origin. 2. Understand terms used to describe the textures of igneous, metamorphic & sedimentary rocks. 3. Be able to use and understand the classification scheme provided for each rock type and be able to recognize or name some of the more common rocks by sight. Introduction Last week we learned to identify some of the major rock-forming minerals. This week will build upon that extensive experience to understand better the rocks and their geologic significance. To an earth scientist, rocks represent much more than usable substances. They are the material of the earth understanding their origin and distribution helps us understand the earth and some of the major processes involved in changing the earth. It is often said (mostly by geologists) that “the history of the earth is written in the rocks” - we just have to be smart enough to read the "words." This week’s lab will allow you to investigate some of the common rocks that are found on and near the surface of the earth. The criteria used to classify igneous, sedimentary or metamorphic rocks will be examined, as well as the procedures in identifying rocks within each of these categories. Rocks... what are they?? For thousands of years rocks have proven their usefulness because of their durability and beauty. Granite and limestone are widely used as building materials and decorative coverings. Slate is utilized for hard, enduring table surfaces (such as pool tables) and fine marble have been used by sculptors for centuries to display their artistic talents. Rocks are mostly mixtures of one or more minerals and are classified into three main groups based on the processes that formed them. 1. Igneous Rocks: rocks formed from the cooling and solidification of magma or a lava. Magma: molten rock that forms naturally within the Earth. Magma may be either a liquid or a fluid mixture of liquid, crystals and dissolved gases. At the Earth's surface, magma is called lava. 2. Sedimentary Rocks: a rock formed by the consolidation (lithification) of sediments, it may consist of fragments and mineral grains of varying sizes from pre-existing rocks, the remains or products of animals and plants, or the or by precipitation of minerals from solution. 3. Metamorphic Rocks: igneous or sedimentary rocks that have been changed or altered by conditions of elevated temperature and/or pressure within the earth. THE ROCK The Rock Cycle: One of the most useful devices CYCLE for understanding rock types and the geologic processes that transform one rock type into another is the Rock Cycle. Through the course of time rocks are created, destroyed and altered through a set of internal and external processes operating on the earth. The rock cycle is an attempt to describe the series of events by which rocks are transformed from one type of rock to another over time. 1 ROCK IDENTIFICATION Texture and Composition When we identified minerals, we used the physical and chemical properties of the mineral. Rocks, however, are aggregates of one or more minerals. To recognize and identify the various rocks we will encounter in this course one must first be able to recognize the mineralogical composition of the rock and then the texture of the rock. 1. Composition refers to the minerals that are found in a rock. Often the larger mineral grains can be identified by sight or by using their physical properties. In some cases, small mineral grains may require the use of some magnifying device (microscope or hand lens) to assist in their identification. Occasionally, very small grains cannot be identified with the equipment that you have available - this is where practice and familiarity with the minerals will make your life much easier. 2. Texture refers to the shape, arrangement and size of mineral grains making up a rock. The shape and arrangement of mineral grains help determine the type of rock (e.g. igneous, metamorphic or sedimentary). Mineral grain size is then often used to classify rocks of a particular type. Each rock type uses different terms to describe textures... be sure to understand which terms are used for each rock type. Identification The first step in the identification of rocks is to determine the rock type. Each of the three rock types has a somewhat unique appearance that helps to distinguish one type from the other. This is often a lot harder than it sounds and you should rely on the talents and experience of your friendly instructor to help you learn this procedure. Table 1 gives some of the basic “Rules of Thumb” in identifying different rock types... look them over and become familiar with the characteristics associated with each. Table 1 Rules of Thumb Used in Identifying Different Rock Types IF THEN PROBABLY IT IS Rock shows a crystalline texture, that is, it seems to be made of random interlocking crystals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IGNEOUS Rock is glassy or comprised of many cavities or air holes (gas bubbles) . . . . . . . IGNEOUS Rock shows a clastic texture composed of randomly arranged mineral, rock and/or fossil fragments that are physically bound together . . . . . . . . . . . . . . SEDIMENTARY Rocks that are soft, or not very cohesive, they crumble apart easily into individual grains between one’s fingers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SEDIMENTARY Rocks that are visibly layered or have a tendency to break along bedding planes or contain fossils or fossil fragments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SEDIMENTARY Rock fizzes in acid, contains fossil fragments or is very fine grained. . . . . . . . . . SEDIMENTARY Rock fizzes in acid, consists of coarse interlocking crystals of equal size . . . . . . METAMORPHIC Rock contains crystals that are aligned or arranged so that they lie in same direction. These tend to contain abundant mica, garnets or amphibole. . . . . . . . . METAMORPHIC Rocks that are harder, denser of more compact, with a shiny or glittery 2 appearance on broken surfaces. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . METAMORPHIC LAB 2, IGNEOUS ROCKS Igneous Rocks: rocks formed from the cooling and solidification of a magma or lava. Igneous Rocks are classified on the basis of two properties: (I) Texture, and (II) Mineralogy I. Textural: the size, shape, and arrangement of the minerals making up the rock. A. Aphanitic: a texture of found in igneous rocks in which the crystals are too small for individual minerals to be distinguished with the unaided eye, ex. basalt, andesite and rhyolite. Extrusive Rocks: igneous rocks that formed or crystallized at the Earth's surface. B. Phaneritic: igneous rock texture in which crystals are roughly equal in size and large enough that individual minerals can be identified with the unaided eye, ex. gabbro, diorite and granite. Intrusive Rocks: igneous rocks that formed or crystallized below the Earth's surface. C. Glassy: term used to describe the texture of certain volcanic rocks such as obsidian, which contain no crystals. This texture results from extremely rapid cooling of lava in air or water. D. Vesicular: a term reserved for extrusive igneous rocks that contain small, spherical cavities called vesicles. These form when gases (dissolved volatiles) escape from a lava as it cools. ex. scoria = a dark-colored (basaltic) rock with so many vesicles that is almost looks like a piece of Swiss Cheese); pumice = a light-colored rock consisting of volcanic glass with so many tiny vesicles and so light in weight that is able to float in water (it appears to be almost a froth of volcanic glass). E. Pyroclastic or Fragmental: an igneous rock texture resulting from the consolidation of volcanic ash, dust, or rock fragments that are ejected during a violent eruption. ex. tuff = a general term for pyroclastic rocks in which fragments are less than 2 mm in size, volcanic breccia = fragments are greater than 2 mm. II. Igneous Rock Mineralogy: igneous rocks are classified on the basis of the relative proportion of various silicate minerals. Phaneritic Texture Peridotite Aphanitic Texture - Felsic Minerals Mafic Minerals (see below) Rock Density Major Temp. Color (g/cm3) Cations (deg. C) (see below) Olivine, Pyroxene dark 3.3 Fe, Mg 1200º ------------------------------------------------Pyroxene, Gabbro Basalt Ca-Plagioclase dark 2.9-3.0 Ca, Fe, Mg 1000º minor olivine -------------------------------------------------interDiorite Andesite Na-Plagioclase Amphibole, Biotite mediate ------------------------------------------------Quartz, K-feldspar, Biotite, Granite Rhyolite Na-Plagioclase, minor Amphibole light 2.7 K, Na, Al, 560º Muscovite silica rich 3 Igneous Rock Chemistry: igneous rocks can also be classified on the basis of chemical composition that is reflected in the types of minerals found present in the rock. A. Felsic: Light-colored minerals with relatively low specific gravities; enrich in K, Na, Al and silica (> 65% by weight); & tending to crystallize a lower temperatures (includes the following: Na-rich Plagioclase, K-Feldspar, Muscovite mica, Quartz). The term is used to describe either the igneous rock or minerals that make-up the rock. Includes Rhyolite and Granite. B. Intermediate: rocks with a chemical composition between that of felsic and mafic rocks. These are medium-gray or medium-green in color with Na-rich Plagioclase making up 30-50% of the rock. Silica ranges from 53 to 65% by weight; mafic minerals may include amphibole or biotite; no quartz is present. Includes Andesite and Diorite. C. Mafic: rock composed of dark-colored minerals with a relatively high specific gravity; are rich in Fe & Mg; poorer in silica (45 to 52% by weight); & tend to crystallize a higher temperatures (includes: Olivine, Pyroxene, Amphibole, Biotite mica). The term can be used to describe either the igneous rock or minerals that make-up the rock. Includes Basalt and Gabbro. D. Ultramafic: rocks composed mostly of ferromagnesian (Fe, Mg-rich) minerals (i.e., Olivine, Pyroxene). Silica content is generally < 45% by weight. Includes Peridotite. 4 Plate Tectonics Lab (GLY 108) Igneous Rocks, Lab 2 Here is the list of igneous rocks that we’ll look at for this lab: Andesite, Basalt, Diorite, Gabbro, Granite, Obsidian, Pumice, Rhyolite and Scoria Color of Rock Texture of Rock Mineral light, intermediate, phaneritic, aphanitic, what minerals do you see or dark colored? vesicular, etc.? Origin or Interpretation Igneous Rock Name or what might be present? intrusive or extrusive? 19 Diorite 20 Pumice 21 Scoria 22 Rhyolite 23 Granite 24 Andesite 25 Gabbro 26 Basalt 27 Obsidian 5 Plate Tectonics Lab (GLY 108) Igneous Rocks, Lab 2 Questions: 1. If you had a sample of granite, what would be its texture? What about obsidian? Andesite? Why? 2. Which of the following rocks cooled slowly at depth: granite or basalt? How do you know? 3. Which of the following rocks cooled at the highest temperature: granite, diorite, or gabbro? How do you know? 4. Which of the following rocks cooled at the lowest temperature: rhyolite, andesite, or basalt? How do you know? 5. Which of the following rocks cooled quickly from a volcano: obsidian or diorite? 6 GLY 108 – Plate Tectonics: The Active Earth Lab 4: Metamorphic Rocks Objectives: 1. Examine a rock and determine if it is igneous, metamorphic or sedimentary in origin. 2. Understand terms used to describe the textures of igneous, metamorphic & sedimentary rocks. 3. Be able to use and understand the classification scheme provided for each rock type and able to recognize or name some of the more common rocks by sight. Metamorphic rocks are formed by the alteration of preexisting rock deep within the earth (but still in a solid state). This alteration is caused by heat, by pressure and/or by hot, chemically active fluids passing through the rock. One of the main ideas of the rock cycle is the principle that most minerals and rocks are stable only under the conditions under which they formed. Raise or lower the temperature or pressure, and they become unstable and transform into new mineral and rocks that are stable under the new conditions. Metamorphism is the alteration or a rock through heat and pressure, but short of melting. The original rock prior to metamorphism is called the parent rock. The parent rock can be any preexisting rock, igneous, sedimentary, as well as other metamorphic rocks. Causes of Metamorphism: A. Heat: metamorphism is thought to begin anywhere from 200° C (400° F) and extends to temperatures at which the rock would normally begin to melt, 600° to 800° C (1100° to 1500° F). Potential sources of heat include: 1. Burial Depth and the Geothermal Gradient: As one descends into the interior of the earth the temperature increases an average of 25° C per kilometer burial depth (≈ 100° F per mile). The source of this heat is derived from (1) the confining pressure applied to rocks as a result of burial (as pressure is applied to any material its temperature increases due to frictional interference between atoms) and (2) the decay of various radioactive isotopes present in the rocks deep with the Earth’s interior. (Note: one of the byproducts from the decay of unstable, radioactive isotopes is the generation of heat energy) 2. Igneous Intrusions: Heat may also be derived from any hot, intrusive igneous rocks that are nearby. Here temperatures may reach as high as 900° C adjacent to the intrusion, but gradually decreases with increasing distance away from the intrusion B. Pressure: Pressure is the force applied to a rock at single point and is commonly measured in a unit called a bar. One (1) bar is equal to 14.7 lbs/in2 (or 1.04 km/cm2). Metamorphism is thought to begin at around 1000 bars (this equals 1 kilobar). Under normal conditions this equals the pressure at a depth of about 3.7 km (2.3 mi) and is called lithostatic pressure or confining pressure. 1. Lithostatic Pressure or Confining Pressure: The force exerted on rock buried deep within the Earth by overlying rocks. Because lithostatic pressure is exerted equally from all sides of a rock, it compresses the rock into a smaller, denser form. 2. Differential Pressure or Directed Pressure: Along with lithostatic pressure, rocks may also experience differential pressure. Here pressure applied predominately in one  direction, rather than uniformly from all sides. Differential pressure typically occurs during the deformation associated with mountain building episodes and produces a very distinctive set of metamorphic textures and minerals. Types of Metamorphic Rocks: (Foliated and Nonfoliated Metamorphic Rocks). A. Foliated: a metamorphic rock texture that gives rocks a layered appearance. This is due to the parallel alignment of linear or planar minerals or to compositional banding. 1. Slate: Slate is a compact, fine-grained foliated metamorphic rock composed of minute mica flakes and quartz and exhibits slaty cleavage. This is the tendency of rock to split along closely spaced, parallel planes of breakage, similar in appearance to a deck of playing cards. The rock is the metamorphic equivalent of a shale or mudstone or tuff. 2. Phyllite: Phyllite is a coarser grained, foliated metamorphic rock composed of mica flakes and quartz and commonly formed by the regional metamorphism of shale/mudstone or tuff. Micas characteristically impart a silky sheen to the rock cleavage surfaces. This rock exhibits what we call phyllitic cleavage and is more coarse-grained than slate. 3. Schist: Schist is a medium to coarse-grained, strongly foliated metamorphic rock displaying schistosity = a type of foliation characteristic of coarse-grained metamorphic rocks that have a parallel arrangement of platy minerals such as mica and splits easily into flat, parallel slabs. 4. Gneiss: A coarse-grained, high grade foliated metamorphic rock marked by bands of light-colored minerals such as quartz and feldspar that alternate with bands of darkcolored minerals (e.g., micas or amphibole). 200° to 400° C (1-6 kilobars) 500° to 800° C (12-15 kilobars) Slate ———> Phyllite ———> Schist ———> Gneiss compaction, reorientation & - further mineral growth - Mineral segregation recrystallization of minerals & recrystallization or separation ― increasing heat and pressure, i.e., increasing metamorphic grade → Metamorphic Grade: This measure is used to identify the degree to which a metamorphic rock has changed from the original parent rock. Metamorphic grade provides some indication of the circumstances under which the metamorphism took place. B. Nonfoliated: A metamorphic rock texture that does not exhibit foliation, these are not composed of flat/elongate minerals but consisting of interlocking crystals of equal size. 1. Marble: Marble results from the contact and regional metamorphism of limestone or dolostone. 2. Quartzite: Quartzite results from the contact and regional metamorphism of quartz sandstone. 3. Anthracite: Anthracite is a low-grade metamorphic rock resulting from the regional metamorphism of bituminous coal. Anthracite is shiny with a conchoidal fracture. Environments or Types of Metamorphism: A. Regional Metamorphism: This is a type of metamorphism that occurs over a vast geographic area (in many cases covering hundreds or even thousands of square kilometers) and caused by the downwarping, burial and deformation of large portions of the Earth's crust. Regional metamorphism is often associated with episodes of mountain building. 1. Characterized by elevated temperatures and pressures. 2. Results in foliated, as well as nonfoliated rock textures. B. Contact Metamorphism: Metamorphism at or near a contact between an igneous intrusion and the host rock or country rock. This results in mineralogical and textural changes in the host rock. 1. Characterized by elevated temperatures alone. 2. Results in nonfoliated rock textures. Regional Metamorphism Contact Metamorphism LAB 4, METAMORPHIC ROCKS IDENTIFICATION KEY FOR METAMORPHIC ROCKS Texture Physical and Mineralogical Characteristics Dense, finegrained with Individual mineral a dull luster grains not visible Fine-grained, glossy or lustrous sheen Good one directional cleavage, color variable, dense, minerals grains are microscopic = micas, chlorite, quartz Cleavage not well developed, color variable; minerals are barely visible; shows wavy crumpled structure; mica Foliated Biotite, muscovite or chlorite evident Breaks into thin quartz present though not visible; wavy slabs garnets or staurolite may be present; Individual mineral shows a wavy or crumpled structure grains visible Minerals occur Granitic minerals: feldspar; quartz in coarse bands interlayered with thin layers rich in or layers amphibole and/or biotite mica Nail cannot Fused quartz grains; color variable, light gray to red scratch rock or brown in color Nonfoliated Nail can scratch Reacts to acid; color variable; may be streaked with rock, but harder color; med. to coarse calcite calcite or dolomite than fingernail Black; shiny luster; light weight; conchoidal fracture Rock Name Slate Phyllite Schist Gneiss Quartzite Marble Anthracite Type of Parent Rock or Rock Prior to Being Metamorphosed Shales, mudstones, fine-grained igneous rocks and tuffs Shales, mudstones, fine-grained igneous rocks and tuffs Shales, mudstones, fine-grained igneous rocks Shales, arkoses and/or felsic igneous rocks Quartz sandstones, quartz-rich siltstones Limestone and/or dolostone Bituminous Coal Rock Name Slate Phyllite Schist Gneiss Quartzite Marble Anthracite Plate Tectonics Lab (GLY 108) Name Metamorphic Rock Identification Chart, Lab 4 Using the Identification Key for Sedimentary Rocks from the previous page, try to identify the following set of sedimentary rocks. Be sure to fill in the Identification Chart below as you identify the physical properties of each specimen. Foliated or Nonfoliated Mineralogical Composition Type/Grade of Metamorphism Possible Type of Parent Rock Metamorphic Rock Name 67 Slate 68 Marble 69 Quartzite 71 Mica Schist 73 Phyllite 74 Gneiss 75 Anthracite Coal
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