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Chapter 4 ROCKS Big Question WHAT CHARACTERISTICS DO GEOLOGISTS USE TO IDENTIFY ROCKS? WHAT CHARACTERISTICS DO GEOLOGISTS USE TO IDENTIFY ROCKS? When studying a rock sample, geologists observe the rock’s mineral composition, color, and texture. Texture – the look and feel of the rock’s surface. Grain Fine grain Coarse grain No visible grain Grain shape Rounded Jagged Grain size pattern Nonbanded banded Big Question WHAT ARE THE THREE MAIN TYPES OF ROCKS? WHAT ARE THE THREE MAIN TYPES OF ROCKS? The three main types of rocks are igneous rocks, sedimentary rocks, and metamorphic rocks. IGNEOUS ROCKS Color - depends Mineral Composition Silica – a material formed from oxygen and silicon. Texture The texture of an igneous rock depends on the size and shape of its mineral crystals. Formation Igneous lava. rocks form from the cooling of magma or IGNEOUS ROCKS Types Extrusive – igneous rock formed from lava that erupted onto Earth’s surface. Intrusive – igneous rock that formed when magma hardened beneath Earth’s surface. Uses Tools Building materials Cleaning and polishing SEDIMENTARY ROCK Color - depends Mineral Composition - depends Texture - depends Formation Sedimentary rock forms when particles of other rocks or the remains of plants and animals are pressed and cemented together. In erosion, running water, wind, or ice loosen and carry away fragments of rock. Deposition is the process by which sediment settles out of the water or wind carrying it. Compaction is the process that presses sediments together. Cementation is the process in which dissolved minerals crystallize and glue particles of sediment together. SEDIMENTARY ROCK Types Clastic rock is a sedimentary rock that forms when rock fragments are squeezed together. Organic rock forms where the remains of plants and animals are deposited in thick layers. Chemical rock forms when minerals that are dissolved in a solution crystallize. Uses Building materials Tools Industrial uses Cement Steel METAMORPHIC ROCK Color – depends Mineral Composition – depends Texture – depends Formation Metamorphic rock forms when an existing rock is changed by heat, pressure, or chemical reactions. Types Foliated rocks are metamorphic rocks that have their grains arranged in parallel layers or bands. Nonfoliated rocks are metamorphic rocks which have mineral grains that are arranged randomly. METAMORPHIC ROCK Uses Building Sculpture Marble Flooring Roofing chalkboards Big Question WHAT IS THE ROCK CYCLE? WHAT IS THE ROCK CYCLE? The rock cycle is a series of processes on Earth’s surface and in the crust and mantle that slowly change rocks from one kind to another. Forces deep inside Earth and at the surface produce a slow cycle that builds, destroys, and changes the rocks in the crust.
