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The Rock Cycle What is a Rock? 1. A rock is a hard substance composed of one or more minerals 2. They are the building blocks of the Earth 3. Man has used rocks for tools, weapons, and for buildings for millions of years 4. Rocks are placed into three groups according to how they form: igneous, sedimentary, and metamorphic Igneous Rocks Originally were hot, fluid magma inside the Earth Ignis, comes from Latin, it means fire Sedimentary Come from sediments that were carried along by wind and water Over time these sediment become cemented together to form rock Metamorphic When chemical changes occur in existing rock either by tremendous heat and/or pressure rocks metamorphosis, or change Meta means change, morph means form Metamorphic = to change form The Rock Cycle Rocks are subject to change Igneous and sedimentary rocks can change into metamorphic by heat and pressure Sedimentary and metamorphic rocks can change into igneous rocks by complete melting and solidifying Igneous and metamorphic rocks can change into sedimentary rocks through erosion ******************************************************************************************** Igneous Rock Igneous rocks form when magma cools and makes crystals. 1. INTRUSIVE: forms underground (IN the ground), where the magma cools slowly resulting in large crystals. 2. EXTRUSIVE: forms above ground (EXIT the earth), where the magma cools quickly resulting in small crystals 3. Volcanic igneous rocks: formed from molten rock that cooled quickly on or near the earth's surface. 4. Plutonic igneous rocks: are the result of the slow cooling of molten rock far beneath the surface of the earth. Plutons: classified according to their shape, size and position in the surrounding rock Classification Igneous rocks are classified according to their composition and texture Composition: minerals from which the rock formed Texture: the shape, size, arrangement and distribution of the minerals that make up the rock Textures Glassy: Textures are referred to as glassy (obsidian) when you can not see the crystals Aphanitic: fine grained (basalt) very small interlocking crystals, very difficult to see with the “naked” eye Phaneritic: coarse grained (granite) interlocking crystals roughly the same size Porphyritic (Trachtye) large crystals scattered on a background of smaller crystals Felsic: light colored, high silica content, contains quartz and feldspars Mafic: dark colored, lower silica content, contains iron and magnesium Ultramafic: low silica content, very high levels of iron and magnesium, very rare The more silica the lighter the color Magma composition All igneous rocks are made of magma. The silica content affects melting temperature and impacts how quickly the magma flows BASALTIC: contains 50 % silica (makes basalt) ANDESITIC: contains 60 % silica (makes andesite) RHYOLITIC: contains 70 % silica (makes rhyolite) Main factors involved in the formation of magma are temperature, pressure, water content and mineral composition Veins At the end of the crystallization process mineral rich fluid fills voids and cracks in the surrounding rock. The fluid solidifies and can form veins of gold (or other rare minerals) Pegmatites: Veins of extremely large grained minerals. This is where most of the gem stones are found Kimberlites: Found in rare ultramafic rock, can only form extremely deep and under very high pressure. Diamonds are only found in these deposits (mostly in S. Africa) 1. 2. 3. 4. 5. What characteristics are used to classify igneous rocks? How are intrusive rocks similar to extrusive rocks? How are they different? What determines the size and types of crystals in rocks? What is the relationship between a rock’s texture and where it was formed? What feature is most likely to contain diamonds? ******************************************************************************************** Sedimentary Rocks: Slowly Built Layers Sedimentary rocks are classified according to the origin of the material that they are made from: Clastic, Organic, Chemical Clastic Clastic sedimentary rocks are made from the fragments of existing rocks They are further classified according to the size and shape of the fragments they are made of Conglomerate / Breccia These are made from pebbles cemented together with mud, clay, or sand Over one third is made of pebbles Sandstone Made from particles the size of sand At least half of the material must be sand to be classified as sandstone Grains are cemented together by minerals Most common sedimentary rock Shale / Mudstone Made from particles smaller than sand Made from small particles of mud and clay Most can be split into flat pieces Organic Rocks Organic sedimentary rocks are made either directly or indirectly from material that was once living Limestone May be produced by the shells of once living organisms Living organisms may produce limestone directly as in coral reefs Chalk Fine grained limestone made from microscopic shells Coal Formed from the remains of plants that lived millions of years ago Chemical Rocks Formed when a sea or lake dries up leaving behind large amounts of minerals Minerals can be deposited in caves This category includes rock salt, gypsum, and some limestone The Making of Sedimentary Rocks Erosion and weathering of parent rock Transportation of sediments Deposition of sediments Compaction and cementation of sediments Lithification which turns the sediments into sedimentary rocks ******************************************************************************************** Metamorphic Rock Metamorphic rocks are rocks that have "morphed" into another kind of rock. These rocks were once igneous or sedimentary rocks. The rocks are under tons of pressure, which fosters heat build up, and this causes them to change. Formed from older "parent" rock (either igneous or sedimentary) under intense heat and/or pressure at considerable depths beneath the earth's surface. Types of Metamorphism Regional: Large areas of the Earth’s crust has been metamorphosed Contact Contact: When molten rocks come in contact with solid rock, metamorphic effects decrease farther away from the intrusion of molten rock Hydrothermal Hydrothermal: Very hot water reacts with rock, dissolves some minerals, breaks down minerals and forms new minerals Textures Foliated: wavy layers and bands, most common is schist Nonfoliated: blocky crystal shapes, quartzite and marble Porphyroblasts: a large mineral crystal in a metamorphic rock, found in both regional and contact, some crystals grow much larger than the surrounding crystals Common Metamorphosed Rock Igneous Metamorphic Limestone Marble Shale Slate Sandstone Quartzite Granite Gneiss Basalt Schist Deeper in the Earth with higher pressure metamorphic can morph into new metamorphic EX: Schist can become Gneiss •What does a rock want to be when it gets older? Questions 1. How does the chemical composition of a rock change during metamorphism? 2. Name the three main types of metamorphism. 3. What causes foliated textures? 4. What parts of the rock cycle occur deep within the Earth?