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ROCKS

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What is a Rock?

The material that makes up the solid parts of Earth is known as rock.

Three major types:• Igneous• Sedimentary • Metamorphic

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Properties of Rocks

Physical and chemical properties of rock is determined by how and where it’s formed.

The rate at which rock weathers and the way that rock breaks apart are determined by bond strength and composition. stability

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The Rock Cycle

Any of the three major types of rock can be changed into another of the three types.

Rock cycle the processes in which rock forms, changes, is destroyed, and forms again by geological processes

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Stages of the Rock Cycle Magma forms when rocks melt.

Igneous rock forms when magma, or molten rock, cools and hardens.

Sedimentary rock forms when deposited sediment is compressed and cemented together

Sediments are rocks and other matter that has been broken into fragments by weathering and erosion.

Metamorphic rock forms when existing rock is altered by heat and pressure.

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Bowen’s Reaction SeriesIllustrates the order in which minerals

crystallize from cooling magma according to their chemical composition and melting point

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Rock melts when…

the temperature increases to above its melting point

excess pressure is removed from rock that is hotter than its melting point.

fluids are added. Presence of fluids generally decreases the melting point.

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Partial Melting

Different minerals have different melting pointsLower melting points melt first

As minerals melt, the magma’s composition changes.

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Fractional Crystallization

The crystallization and removal of different minerals from the cooling magma is called

When magma cools, the cooling process is the reverse of the process of partial melting.

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Types of Igneous Rock

Intrusive forms from the cooling and solidification of magma beneath Earth’s surface

Extrusive forms from the cooling and solidification of lava at Earth’s surface

The texture of igneous rock is determined by the size of the crystals in the rock, which is determined by the cooling rate of the magma.

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Igneous Textures

Coarse-GrainedBecause intrusive igneous rocks cool

slowly, they commonly have large mineral crystals.

Fine-Grained

Because extrusive igneous rocks cool rapidly, they are commonly composed of small mineral grains.

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Other Igneous Rock Textures

Porphyritic texture- large crystals within a matrix of smaller crystals.

Phaneritic- crystals all same size

Aphanetic- crystals too small to see

Glassy Texture- no crystalsVesicular texture- dissolved gases are trapped as bubbles in the rock.

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Igneous Composition

Determined by the chemical composition of the magma from which came.

Felsic RockRich in feldspars and silica and is

light in color

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Igneous Composition

Mafic RockRich in magnesium and iron and dark

in colorIntermediate Rockscontain lower amount of silica than

felsic but higher amounts of silica than mafic.

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Extrusions

Igneous rock masses that form on Earth’s surface.

Volcanoes, lava flows, and tuff layers are other common extrusions.

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Intrusive v. Extrusive

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Sedimentary Rock

Made of combinations of different types of sediment, such as fragments of rock, minerals, and organic materials.

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LithificationProcess of loose sediment is converted

into sedimentary rock by compaction and cementation.

compaction the process in which sediment is pressed together by the weight of overlying layers

cementation the process in which minerals bind sediments together to form rock

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Types of Sedimentary RockThere are three main classes of

sedimentary rocks—chemical, organic, and clastic.

Classification is based on the shape, size, and composition of the sediments that form the rocks.

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chemical sedimentary rock

Forms when minerals precipitate from a solution or settle from a suspension

Rocks that form through evaporation are called evaporites. Gypsum and halite

(table salt) are common evaporites.

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organic sedimentary rock Forms from the

remains of plants or animals Coal Organic

limestones▪ Dead shells

accumulate and are compacted to form limestone.

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clastic sedimentary rock Forms when

fragments of preexisting rocks are compacted or cemented together

Clastic sedimentary rocks are classified by the size of the sediments they contain.

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Types of clastic sedimentary rock

Conglomerate- contains large, rounded pieces.

Breccia- contains large, angular pieces.

Sandstone- composed of sand-sized grains.

Shale- composed of clay-sized particles.

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Physical Characteristics of Sediments

Sediments are transported by four main agents: water, ice, wind, and the effects of gravity.

The distance it is moved and the agent that moves it determine the characteristics of that sediment.

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Sorting

The tendency for sediments to separate according to size. Well-sorted = same size and shape. Poorly sorted = many different sizes.

Faster-moving currents can carry larger particles than slower-moving currents can.

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AngularityAs sediment is transported it collides with

other objects. Causes the particles to change size and

shape.

When particles first break from the source rock they tend to be angular and uneven.

In general, the farther sediment travels from its source, the finer and smoother the particles become.

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Stratification

Layering of sedimentary rock which occurs when the conditions of sediment deposition change.

Stratified layers are called beds.Depositional environment- setting in

which sediment is deposited

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Sedimentary FeaturesCross-Beds and Graded

Bedding

Cross-beds, or slanting layers of rock, form in sand dunes or river beds.

Graded bedding is a feature in sediments are deposited with the larger grains at the bottom and finest grains at the top.

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Sedimentary FeaturesRipple MarksRipple marks form

when air or water flows over sand and the ripples are preserved in the rock. Commonly at the

beach or on a river bed.

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Sedimentary Features Cont’dMud Cracks

Mud cracks form when muddy deposits dry and shrink. The shrinking causes the drying mud to crack.

Mud cracks form on river floodplains or on dry lake beds.

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Sedimentary Features Cont’dFossils and

ConcretionsFossils are the remains

of organisms that are preserved in rock.

Concretions are lumps of minerals that precipitate from fluids and build up around a nucleus or in a cavity in existing rock.

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Metamorphism Process in which one type of rock changes into

metamorphic rock

During metamorphism, heat, pressure, and hot fluids cause some minerals within the rock to change.

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Factors Affecting Metamorphism

The type of rock that forms indicates the conditions under which the original rock changed.

Factors Affecting Metamorphism Composition of the parent rock The amount and direction of pressure The presence or absence of fluids

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Types of MetamorphismContactMetamorphismChange in the

texture, structure, or chemistry of rock due to contact with magma

HydrothermalMetamorphismVery hot water

reacts with rock

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Types of MetamorphismRegionalMetamorphism

Change in the texture, structure, or chemistry of rock due to occurring over a large area, generally are a result of tectonic forces

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Metamorphic TexturesFoliated RocksMinerals grains are

arranged in planes or bandsExtreme pressure may

cause the mineral crystals in the rock to realign into alternating light and dark parallel bands. Foliated metamorphic rocks

include the common rocks slate, schist, and gneiss.

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Metamorphic TexturesNonfoliated Rocks

Minerals grains are not arranged in planes or bands

Some tend to be less diverse in chemical compositions than foliated metamorphic rocks.

Others contain grains that have more stable structure and do not change shape as readily as a result of temperature and pressure changes Ex: marble and quartzite.

Geologic Map of Alabama