Transcript Chapter 4
Chapter 4 Rocks Classifying Rocks Section 1 Why must scientists who study rocks look at the inside of them? Because the outside surfaces have been exposed to the effects of ice, water, and weather (Erosion). Mineral composition and color 2. What three important things do scientists observe when studying rocks? -Mineral composition, color, and texture 3. What are rock forming minerals? -About 20 minerals that are found in the earth’s crust that make up rocks. 4. What minerals are found in granite? -Quartz, horneblende, mica, and feldspar Mineral Composition: (This is also in the igneous section on page 2) Most of Earth’s (rocks) contain Silica Silica is a material formed from oxygen and silicon. The silica content of magma and lava will affect the types of rock that form High silica usually forms light colored rocks Low silica usually forms dark colored rocks 5.Some other ways scientists study rocks include: Shape and color of the crystals Mineral content Color Texture And some other tests similar to the tests for minerals Texture Grains- Give the rock texture What is texture? Texture is the look and feel of the rocks surface. The three grain sizes that make texture are: 1. Fine 2. Coarse 3. No visible Texture: Grain Size Coarse grained = large grains and easy to see Fine grain = microscopic and too small to see There are three main groups of rocks Igneous – forms from cooling of magma or lava Sedimentary – forms when particles of other rocks or the remains of plants and animals are pressed and cemented together Metamorphic – forms when and existing rock is changed by heat, pressure or chemical reactions, forms deep underground There are two grain shapes: 1. 2. Jagged Round There are two grain patterns: 1. Banded 2. Non- banded Igneous Rocks Section 2 Igneous Rocks An igneous rock is any rock that forms from magma or lava. The name “igneous” comes from the Latin word meaning “fire” Igneous rocks come from deep within the ground Igneous Rock Identification Igneous rocks are classified according to origin, texture and mineral composition Origin Texture Mineral composition Intrusive and Extrusive Extrusive rock is formed from lava that erupted onto the earth’s surface. Intrusive rock is formed when magma hardens beneath the surface. Molten rock below the earth’s surface is called magma. When it makes it to the surface it is called lava. Igneous ID Questions 5-7 Texture: depends on the size and shape of the mineral crystals. The only exceptions are those rocks made of glass. Rapidly cooling lava forms fine-grained rock Slowly cooling lava forms coarse-grained rocks with large crystals Intrusive rocks should have coarse-grained texture while extrusive rock will have fine-grained texture. Igneous Rocks Continued Most of the earth’s rocks contain the mineral silica. Silica content of rocks can affect the rocks color. Examples of Igneous rocks: Rhyolite, Porphyry, Pegmatite, Granite, etc. Uses of Igneous Rock Building Material Cleaning and polishing granite Pumice Sharp tools for cutting or scraping obsidian Sedimentary Rocks Section 3 Sedimentary Rock Sediment - small, solid pieces of material that come from rock or living things. Ex. rock, shells, bones, leaves, stems, etc. Sedimentary rocks are formed through the process of: 1.Erosion 2.Deposition 3.Compaction 4.Cementation Rocks - Sedimentary Rocks From Sediment to Rock Most sedimentary rocks are formed through a series of processes: erosion, deposition, compaction, and cementation. Sedimentary Rocks *Erosion* Erosion- destructive forces including heat, cold, rain, waves, grinding ice, running water, wind and ice loosen and carry it away. (The forces of erosion form sediment) Sedimentary Rocks *Deposition* Deposition - the process by which sediment settles out of the water or wind carrying it Sedimentary Rocks *Compaction* Compaction - the process that presses sediments together Thick layers build up over millions of years The more layers, the more it presses down on the layers beneath them. Sedimentary Rocks *Cementation* Cementation - the process in which dissolved minerals crystallize and glue particles of sediment together While compaction is occurring, the minerals slowly dissolve in the water Sedimentary Rocks 3 major types of rocks Clastic Organic Chemical Sedimentary Rock: Clastic Clastic rock- a sedimentary rock that forms when rock fragments are squeezed together Sediments can range in size Ex. shale, sandstone, conglomerate, breccia Sedimentary Rocks: Organic Organic rock- forms where the remains of plants and animals are deposited in thick layers Ex. coal, limestone Sedimentary Rocks: Chemical Chemical- when minerals that are dissolved in a solution crystallize Ex. rock salt http://www.youtube.com/watch?v=60jof35WuAo http://www.brainpop.com/science/diversityoflife/coral/ Rocks From Reefs Section 4 Rocks from Reefs 1.These rocks are made from the exoskeletons of coral animals. 2. Life can only live within the first 40 meters because that is where there is enough light. 3. The exoskeletons are made from calcium. 4. A coral reef forms when the animals die and their skeletons remain building up over time. 5. Temperatures must be warm. 6.Limestone deposits can tell us that there must have been on ocean or sea there sometime in the past Metamorphic Rocks Section 5 http://www.brainpop.com/science/earthsystem/typesofro cks/ Metamorphic Rocks Heat and pressure beneath the surface of the earth can change any rock into a metamorphic rock. Geologists classify metamorphic rocks according to the arrangement of the grains that make up the rocks Foliated Rocks Non-foliated Rocks Metamorphic Rocks When a rock becomes a metamorphic rock… Its appearance changes Texture changes Crystal structure changes Mineral content changes Metamorphic Rocks Foliated = grains arranged in parallel layers or bands Ex. slate, schist and gneiss Metamorphic Rock Non-foliated = mineral grains are arranged randomly Ex. marble, quartzite Uses of Metamorphic Rocks Two of the most used metamorphic rocks Marble – building and sculptures Lincoln Memorial Slate – flooring, roofing, walkways, chalkboards The Rock Cycle Section 6 The Rock Cycle Forces deep within the Earth and at the surface, produce a slow cycle that builds, destroys, and changes the rocks in the crust. The rock cycle is a series of processes that change rocks from one kind to another. Quartz Sediment Compaction Cementation Sedimentary Rock (sandstone) Buried Pressure Heat Metamorphic Rock (quartzite) What next? ROCK CYCLE ACTIVITY