THREE-TYPES-OF-ROCKS.pdf

MINERALS AND ROCKS  Rocks An aggregate of one or more minerals; or a body of undifferentiated mineral matter (e.g., obsidian); or of solid organic matter (e.g., coal) – More than one crystal – Volcanic glass – Solidified organic matter – Appearance cont...

MINERALS AND ROCKS  Rocks An aggregate of one or more minerals; or a body of undifferentiated mineral matter (e.g., obsidian); or of solid organic matter (e.g., coal) – More than one crystal – Volcanic glass – Solidified organic matter – Appearance controlled by composition and size and arrangement of aggregate grains (texture) Granite: polished section showing aggregate of four interlocking and different coloured minerals Crushed rocks Cement matrix Concrete: non-natural aggregate of other rocks set in a matrix  Coal - biogenic Evaporite - inorganic Biogenic and inorganic sedimentary rocks Limestone - biogenic  ROCK TYPES Igneous Form by solidification of molten rock (magma) Sedimentary Form by lithification of sediment (sand, silt, clay, shells) Metamorphic Form by transformations of preexisting rocks (in the solid state) 3 TYPES OF ROCKS  3 TYPES OF ROCKS There are 3 types of rocks found on Earth: – Igneous – Sedimentary – Metamorphic Knowing the differences between these 3 types of rocks allows us to learn about Earth’s past. IGNEOUS ROCKS  Crystallize! Guide Questions: 1. How many members were formed after the different time intervals? 2. What is the relationship of the time interval to the number of members formed after the time allotted to “crystallize”? 3. Based on this activity, what can you infer about the formation of crystals in rocks?  IGNEOUS ROCKS - FORMATION Igneous Rocks are formed by melting, cooling, and crystallization of other rocks. Igneous rocks form as a result of volcanic activity, hot spots, and melting that occurs in the mantle. Fig. 18. A model that shows how cooling rate affects crystal size.  IGNEOUS ROCKS Igneous rocks are common along plate boundaries or mantle hot spots Types of Igneous Rocks Igneous rocks can be classified based on the temperature-pressure condition during the solidification of magma extrusive and intrusive. Extrusive igneous rock o forms when magma or volcanic fragments erupt and solidify on Earth’s surface which results to very fine-grained rock with very small crystals that could not be seen through naked eye Basalt: igneous extrusive OBSIDIAN PUMICE ANDESITE Intrusive igneous rock Form within the Earth Slow cooling Interlocking large crystals Example = granite GABBRO  DIORITE  As magma rises to the crust, it can displace the host or country rock to form structures. They vary in sizes and shape and may be classified as discordant or concordant structures. – Discordant structures are those that cut across existing structures. An example of discordant structure is a dike. Fig. 22. Intrusive igneous bodies.  Concordant bodies are those that are injected parallel to features in the country rock such as sedimentary beds. An example is a sill. Intrusive and extrusive igneous rocks  IGNEOUS ROCKS - CLASSIFICATION Igneous rocks are classified using their texture in the following ways: – Glassy – Aphanitic (no visible crystals) – Phaneritic (visible crystals) – Porphyritic (Some visible and some not visible crystals)  Types of Igneous Rocks Based on Texture Aphanitic rock has crystals that are too fine-grained to be seen by the naked eye or even with the help of a hand lens Phaneritic rock has grains that are coarse enough to be visible to the eye Pegmatitic rock has crystals are greater than 3 cm due to very slow cooling Vesicular rock contains tiny holes called vesicles due to gas bubbles in the lava or magma Porphyri c are rocks where larger crystals are embedded in smaller crystals Amygdaloidal is when vesicles are filled by low-temperature minerals after the solidification of magma Pyroclastic is formed from the consolidation of individual rock fragments that are ejected during a volcanic eruption.  Types of Igneous Rocks Based on Mineral Composition FELSIC IGNEOUS ROCK is usually light colored and contains large amounts of quartz, potassium feldspar, and plagioclase. It is also called granitic igneous rock. INTERMEDIATE IGNEOUS ROCK is medium gray or medium green and consists of major minerals like amphibole, plagioclase, and feldspar. MAFIC IGNEOUS ROCK is dark gray to black-colored and composed large of plagioclase and amphibole with small amounts of olivine. It is also called as basaltic igneous rock. ULTRAMAFIC IGNEOUS ROCK has a very dark green to black shade and consists largely of olivine and pyroxene.  Igneous Rocks - Texture Crystal size is used to classify igneous rocks. Crystals form as the rock cools, and the crystal size can tell us a lot about its cooling history: – The larger the crystals, the slower it cooled.  Igneous Rocks - Texture Glassy igneous rocks have no crystal structure, and probably formed by very rapid cooling (such as on the surface of a lava, or when a lava enters the water.)  Igneous Rocks - Texture Aphanitic rocks have no visible crystals, and probably formed by fast cooling above ground.  Igneous Rocks - Texture Phaneritic rocks have visible crystals, and probably formed by slow cooling below ground.  Igneous Rocks - Texture Porphyritic rocks have both visible and nonvisible crystals, and probably formed by two different cooling events.  Igneous Rocks - Classification Dark igneous rocks are formed from basaltic or mafic magma. (Mafic because it contains a lot of magnesium and iron). The magma that forms these rocks is usually very hot (around 1000°C) and viscous (about the same viscosity as ketchup.)  Igneous Rocks - Classification Light colored igneous rocks are formed from silicic (high silica content) or felsic magmas. The magmas that form these rocks is usually more cool, (lower than 850°C), and more viscous (about the viscosity of peanut butter.) Bowen’s Reaction Series  Igneous rocks - Formations Structures and formations seen in igneous rocks include: – Hexagonal columnar joints – Pahoehoe lava flows – Dikes, sills, and batholiths (plutons) – Pillow basalts – Volcanoes  Igneous Rocks - Examples The most common types of igneous rocks include: – Rhyolite – Andesite – Basalt – Granite – Diorite – Gabbro Igneous rocks charted  The accompanying photos are examples of common igneous rocks in the Philippines (basalt, obsidian, tuff): Fig. 25 Igneous Rocks (from left to right: basalt, obsidian, tuff) Image Credits: Mines and Geoscience Bureau  Sedimentary Rocks - Formation Sedimentary rocks are formed by weathering, erosion, deposition, compaction, and cementation of other rocks. Sedimentary rocks form in areas where water, wind, or gravity deposit sediments. Figure: Compaction and cementation  Sedimentary rocks - formation Sedimentary rocks are likely to form in areas such as: – Deltas – Beaches – Rivers – Glaciers – Sand dunes – Shallow seas – Deep oceans  Sedimentary rocks - formations Structures and formations seen in sedimentary rocks include: – Stratification – Cross bedding – Graded bedding – Ripple marks – Mud cracks – Fossils  Sedimentary rocks - Examples Some of the most common types of sedimentary rocks include: – Conglomerate – Sandstone – Shale – Limestone – Gypsum – Oolites – Chert (including black flint and red jasper)  Sedimentary rocks - Classification Sedimentary rocks are classified into three groups: – Clastic rocks – Non-clastic Sedimentary rocks  Sedimentary rocks – Classification Sedimentary rocks are Clastic if they are made of pieces of other rocks that have been weathered and eroded. Clastic rocks are grouped based on the size of grain that they are made from.  Sedimentary rocks - Classification Very small particles make up mudrock. Medium sized particles make up sandstone. Large particles make up conglomerates.  Sedimentary rocks - Classification Sedimentary rocks that form from chemical processes are called biochemical rocks (formed from living things) or Chemical precipitates (formed from lakes or shallow seas.)  Non-clastic Sedimentary Rocks 1. Biological sedimentary rocks are lithified accumulation of dead organisms.Examples include coal (formed from carbon-rich plants) and limestone (formed from the remains of calcareous organisms). 2. Chemical sedimentary rocks form from chemical precipitation. An example is rock salt formed when dissolved salts precipitate from a solution. This occurs when there is a change in temperature or level of acidity of the solution.  Below is a table of chemical sedimentary rocks based on composition and texture size. The followings images are examples of sedimentary rocks in the Philippines (chert, coquina, limestone). Fig. 28 Sedimentary Rocks (from left to right: chert, coquina, limestone) Image Credits: Mines and Geoscience Bureau  Metamorphic rocks - Formation Metamorphic rocks are formed by heat and pressure changing one type of rock into another type of rock. Metamorphic rocks form near lava intrusions, at plate subduction zones, and in deep mountain roots.  Metamorphic rocks - Formation Lava intrusions can provide heat that causes metamorphic rocks to form. These small areas of metamorphic rock form from contact metamorphosis.  Metamorphic rocks - Formation Rocks that metamorphose because of increasing heat and pressure found at plate subduction zones and in deep mountain roots form large areas of metamorphic rock through regional metamorphosis. Changes in minerals during metamorphism can happen in three possible ways: Recrystallization small crystals of one mineral will slowly convert to fewer, larger crystals of the same mineral without melting the rock Neomorphism – the process whereby minerals not only recrystallize, but also form different minerals from the same chemical elements Metasomatism – the addition or loss of elements new minerals form with only some of the original elements, and new elements were added through hydrothermal migration (Example: limestone to marble) Types of Metamorphism There are two main scales at which metamorphism can occur: Figure: Contact Metamorphism Contact metamorphism occurs only at a local area adjacent to large intrusions and along fractures that are in contact with hot fluids.  REGIONAL METAMORPHISM occurs at very large areas may occur when there are major igneous intrusions that form and cool over long periods of time. Fig. 30 Regional Metamorphism  Metamorphic rocks - Classification Metamorphic rocks are classified into 2 major groups: – Foliated – Nonfoliated  Metamorphic rocks - Classification Foliated rocks form when differential pressure causes minerals to form in layers. These rocks will have stripes or planes that they will break easily along. These “stripes” don’t usually line up with the original bedding planes in sedimentary rocks. Increasing metamorphism causes distinct bands or foliation to form.  Metamorphic rocks Nonfoliated metamorphic rocks formed in areas where the pressure from all sides was equal, so there is no “linear” quality to the rocks.  Metamorphic rocks - Formations Structures and formations seen in metamorphic rocks include: – Folding – Plastic deformation – Stretching – Alternating dark and light layers (gneissic foliation)  Metamorphic rocks - Examples Some common types of metamorphic rock include: – Slate – Schist – Gneiss – Amphibolite – Marble – Quartzite – Metaconglomerate Metamorphic rocks - Charted Some metamorphic rocks with their corresponding parent rocks or (Protolith)  The followings images are examples of metamorphic rocks in the Philippines (marble, mica schist, slate). SLATE WRAP-UP TS#7: ROCKY ROCKY ROCK A good rock collection is composed of properly labeled specimens that are selected beforehand that best represent a particular rock or rock type. You can start your rock collection by first accumulating three rocks that can be found in your backyard or at school. Draw the rock (with proper scaling) that you collected or you may also choose to take a photograph of it and paste it in the sample worksheet below. Based on the characteristics of each rock type discussed above, determine whether the rocks that you collected can be categorized as igneous, sedimentary, or metamorphic. Each photo below represents one specific rock type. Which of the three represents a sedimentary rock? Explain your answer.