Inside Earth

Chapter 5: RocksSection 1: Classifying Rocks

Mineral Composition and Color

Rocks -made of a mix of minerals and other materialsRocks can contain 1 mineral while others contain several minerals

Rock-forming minerals

Made of quartz, feldspar, hornblende, and micaAbout 20 minerals that make up Earth’s crustGeologists observe shape and color of crystals in rock to id mineral rock containsAcid test

Granite

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Light colored rock that has high silica content

Basalt

Dark colored rock that is low in silica

Texture

Look and feel to the rock’s surfaceSmooth and glassy or rough and chalky

Grains

Particles of minerals or other rocksGive the rock its texture

Grain Size

Large and easy to see=coarse grainedSo small they can only be seen with a microscope=fine-grained

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Grain Shape

Vary widely in shapeSome look like tiny particles of sand, some look like exploding starsGrain results from shapes of crystals that form rock

Grain Pattern

Some grains lie in flat layers that look like stacks of pancakes-BandedForm swirling patterns-NonbandedCan be different colors

How rocks form

3 major groups

Igneous rocks

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Forms from the cooling of magma or lava

Sedimentary Rocks

Forms when particles of other rocks or the remains of plants and animals are pressed and cemented togetherForm in layers that are buried below surface

Metamorphic rocks

Forms when an existing rock is changed by heat, pressure, or chemical reactionsForm deep underground

Inside Earth

Chapter 5: RocksSection 2: Igneous Rocks

Classifying Igneous Rocks

Probably first rocks to form on EarthIgneous from Latin word ignis=fireClassified according to origin, texture, and mineral composition

Origin

Form on or beneath Earth’s surface

Extrusive Rock

Igneous rock formed from lava that erupted on Earth’s surfaceEx: Basalt- oceanic crust, volcanoes, and lava plateaus

Intrusive Rock

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Igneous rock that formed when magma hardened beneath Earth’s surfaceEx: granite, continental crust, core of mtn. ranges

Texture

Depends on size and shape of mineral crystalsRapidly cooling lava=fine grained igneous rock with small crystalsSlow cooling magma=coarse-grained rocks with large crystalsIntrusive rocks=larger crystals EX: porphyryExtrusive rocks=fine grained, glassy texture EX: basalt and obsidian

Mineral Composition

Silica content

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Lava=low in silica, dark colored rocks, EX: basaltMagma= high in silica, light colored rocks, EX: granite

Uses of Igneous Rocks

People throughout history used igneous rocks for tools and building materials

Building Materials

Granite3,500 years ago, Egyptians used it for statues600 years ago Incas build fortress near Cuzco, Peru1800s-1900s U.S.- bridges, public buildings, paving streetsNow-used as curbstones, floors, and kitchen countersBasalt-crushed to make gravel

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Other Uses

Pumice-abrasive for cleaning and polishingObsidian-used by Native Americans to make sharp tools for cutting and scrapingPerlite-formed from heating obsidian-is mixed with soil for planting

Chapter 5: RocksSection 3: Sedimentary Rocks

Inside Earth

From Sediment to Rock

Sedimentary rocks formed through a series of processes: erosion, deposition, compaction, and cementation

Sediment

Small, solid pieces of material that come from rocks and living thingsEX: sand grains, mud, pebbles, shells,

bones, leaves, stems

Erosion

Running water, wind, or ice loosen and carry away fragments of rockHeat and cold, rain, waves, grinding, and ice forces form sediment

Deposition

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Process by which sediment settles out of the water or wind carrying itMoving force deposits sediment in layers, rock and other fragments sink to bottom

Compaction

Process that presses sediments togetherThick layers of sediment build up gradually over millions of yearsHeavy layers press down on layers beneath them, squeezing them togetherLayers remain visible in sedimentary rock

Cementation

Process in which dissolved minerals crystalize and glue particles of sediment together

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Dissolved minerals seep into spaces and harden

Types of Sedimentary Rock

3 groups according to type of sediment that makes up rock

Clastic Rocks

Fragments can range in sizeGrouped by size of fragmentsEX: shale, sandstone, conglomerate, brecciaShale-tiny particles of claySandstone-sand on beaches

Clastic rock

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Sedimentary rock that forms when rock fragments are squeezed together

Organic rock

Forms where remains of plants and animals are deposited in thick layersOnce part of living thingEX: coal-remains of swamp plantsLimestone-forms in ocean from coral, clams, oysters, skeletons made of calcite

Chemical rocks

Minerals are dissolved in a solution crystalizeCertain limestone forms when calcite is dissolved in lakes, seas, underground water solutions

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Rock salt made of halite-formed from evaporation

Uses of Sedimentary rocks

People have used them throughout history for building materials and toolsArrowheads out of flintSandstone and limestone-building materials for 1000s of yearsWhite House in D.C.=sandstone

Inside Earth

Chapter 5: RocksSection 4: Rocks from Reefs

Florida

Coral reef-food and shelter for many sea animalsCity built on billions of skeletons made of calcite

Coral Reefs

Coral animals live together in vast numbersProduce skeletons that grow together to form a structure

Inside Earth

How coral animals live

Smaller than your fingernailUse tentacles to capture and eat microscopic creatures that float byAlgae grow within body of coral animal-algae/coral dependent on each otherNeed sunlight, must be close to surface

How a coral reef forms

Coral animals die, skeletons remain and more corals build on top of them gradually forming a reefCannot grow in cold water, only form in warm, tropical oceansEX: U.S.-Hawaii and Florida

Limestone From Coral Reefs

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Deposits that begun as coral reefs provide evidence of how plate motions have changed Earth’s surfaceProvide evidence of past environments

Inside Earth

Chapter 5: RocksSection 5: Metamorphic Rocks

Metamorphic Rocks

Heat and pressure deep beneath Earth’s surface can change any rock to metamorphic rockAppearance, texture, crystal structure, and mineral content changeCan form from igneous, sedimentary, or other metamorphic rock

Types of Metamorphic Rocks

Geologists classify rocks according to arrangement of grains that make up rocks

Foliated Rocks

Metamorphic rocks that have grains arranged in parallel layers or bandsFoliated=Latin for leaf

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Thin, flat layeringEX: slate, schist, gneiss

Nonfoliated Rocks

Random arrangement of mineral grainsNot split in layersEX: marble, quartzite

Uses of Metamorphic Rocks

Important materials for building and sculptureMarble-used for buildings and statues, Lincoln Memorial in D.C.Slate-comes in variety of colors, used for flooring, outdoor walkways, chalkboards, and trim for buildings

Inside Earth

Chapter 5: RocksSection 6: The Rock Cycle

Rock Cycle

Series of processes on Earth’s surface and in the crust and mantle that slowly change rocks from one kind to anotherForces deep inside Earth and at surface produce slow cycle that builds, destroys, and changes rocks in crust

A Cycle of Many Pathways

Igneous rock formed beneath surface forces of mountain building push rock upward water and wind wear away rock rock becomes sand and is carried to ocean forms sediment and becomes sedimentary rock heat and pressure

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change rock’s texture cycle continues for millions of years

The Rock Cycle and Plate Tectonics

Plate movements start rock cycle help form magma, source of igneous rocksPlate movements cause faulting, folding, other motions of crust that help form sedimentary and metamorphic rocks

Igneous Rocks

Oceanic plate subducted beneath continental plate, magma forms and rises=volcano made of igneous rockContinental/continental collision may cause magma to melt and slowly cool, forming igneous rock

.Sedimentary and Metamorphic Rocks

Inside Earth

Collision of continental plates=faults, folds, and uplift from crustCollision could push up mtn. rangeErosion begins and mtn.’s worn away, sedimentary rock formsContinental plate collision pushes rocks down into mantleHeat and pressure change rock to metamorphic rocks