Rocks: Mineral Mixtures
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Transcript of Rocks: Mineral Mixtures
ROCKS: MINERAL MIXTURESChapter 4
Section 1
The Rock cycle
Introduction Rock: a naturally occurring solid mixture
of one or more minerals and organic matter
Rock cycle: the continual process by which new rock forms from old rock material
Processes that Shape the Earth Weathering, Erosion, and Deposition
Weathering: the process in which water, wind, ice, and heat break down rock
Erosion: the process by which sediment is removed from its source
Deposition: the process in which sediment moved by erosion is dropped and comes to rest Deposited in bodies of water and other low-
lying areas
Processes that Shape the Earth Heat and Pressure
Sedimentary rock made of sediment can also form when buried sediment is squeezed by the weight of overlying layers of sediment
If temperature and pressure are high enough, the rock can change into metamorphic rock
The melting of rocks creates the magma that eventually cools to form igneous rock
Processes that Shape the Earth How the Cycle Continues
Uplift: movement within the Earth that causes rocks inside the Earth to be moved to the Earth’s surface When uplifted rock reaches the Earth’s surface,
weathering, erosion, and deposition begin
Weathering > Erosion > Deposition > Compaction and Cementation > Metamorphism > Melting > Cooling >
Solidification > Weathering
SEDIMENTARY ROCK
METAMORPHIC ROCK
IGNEOUS
ROCK
MAGMA!
SEDIMENT
Sedimentary Rock Grains of sand and other sediment are
eroded from hills and mountains and wash down a river to the ocean. Over time, the sediment forms thick layers on the ocean floor. Eventually, the grains of sediment are compacted and cemented together to form sedimentary rock.
Metamorphic Rock When large pieces of the Earth’s crust
collide, some of the rock is forced downward. At great depths, intense heat and pressure heat and squeeze the sedimentary rock to change it into metamorphic rock.
Magma The hot liquid that forms when rock
partially or completely melts is called magma. Where the metamorphic rock comes into contact with magma, the rock tends to melt. The material that began as a collection of sand grains now becomes part of the magma.
Igneous Rock Magma is usually less dense than the
surrounding rock, so magma tends to rise to higher levels of the Earth’s crust. Once there, the magma cools and solidifies to become igneous rock.
Sediment Uplift and erosion expose the igneous
rock at the Earth’s surface. The igneous rock then weathers and wears away into grans of sand and clay. These grains of sediment are then transported and deposited elsewhere, and the cycle begins again.
Round and Round it Goes Each rock type can
change into one of the three types of rock
As one rock is changed into another type, several variables, including time, heat, pressure, weathering, and erosion, may alter a rock’s identity
Rock Classification Scientists divide all rock into three main
classes based on how the rock is formed Igneous Sedimentary Metamorphic
Can be divided further Divisions based on differences in the way rocks
form Two important criteria for divisions—
composition and texture
Rock Classification Composition
The chemical makeup of a rock; describes either the minerals or other materials in the rock
Rock Classification Texture
The size, shape, and positions of the grains that make up a rock Sedimentary rock: fine-grained, medium-
grained, or coarse-grained texture Igneous rock: fine-grained or coarse-grained
texture Metamorphic rock: fine-grained or coarse-
grained texture
Rock Classification Texture
Can provide clues as to how and where the rock formed
Can reveal the process that formed it
Fine-grained Medium-grained Coarse-grained
Section 2
Igneous rock
Origins of Igneous Rock Forms when
magma cools and solidifies Three ways
magma can form: When rock is heated When pressure is
released When rock changes
composition
Composition and Texture of Igneous Rock
Light-colored rocks are less dense than the dark-colored rocks
Felsic rocks: light-colored rocks rich in elements such as aluminum, potassium, silicon, and sodium
Mafic rocks: dark-colored rocks rich in calcium, iron, and magnesium, and poor in silicon
Composition and Texture of Igneous Rock
The more time the crystals have to grow, the larger the crystals are and the coarser the texture of the resulting igneous rock is
Igneous Rock Formations Located above and below the surface of
the Earth Intrusive Igneous Rock
When magma pushes into surrounding rock below the Earth’s surface and cools
Has a course-grained texture Cools very slowly
Igneous Rock Formations Masses are named for their
size and shape Plutons: large, irregular-shaped
intrusive bodies Batholiths: largest of all
igneous intrusions Stocks: intrusive bodies that
are exposed over smaller areas than batholiths
Dikes: sheet-like intrusions that cut across previous rock units
Sills: sheet-like intrusions that are oriented parallel to previous rock units
Igneous Rock Formations Extrusive Igneous Rock
Igneous rock that forms from magma that erupts onto the Earth’s surface
Common around volcanoes Cools quickly Very small crystals or no crystals
Section 3
Sedimentary Rock
Origins of Sedimentary Rock
Sandstone: sand grains that are compressed and then cemented together over time
Sediment: rock and mineral fragments Deposited in layers Dissolved minerals separate from water that
passes through the sediment to form a natural cement that binds the rock and mineral fragments together in sedimentary rock
Forms at or near Earth’s surface Forms without heat or pressure
Composition of Sedimentary Rock Classified by the way it forms
Clastic sedimentary rock: forms when rock or mineral fragments are cemented together
Chemical sedimentary rock: forms when minerals crystallize out of a solution to become rock
Organic sedimentary rock: forms from the remains of once-living plants and animals
Composition of Sedimentary Rock
Clastic Sedimentary Rock Made of fragments
of rocks cemented together by a mineral such as calcite or quartz
Have coarse-grained, medium-grained, or fine-grained textures
Composition of Sedimentary Rock Chemical Sedimentary Rock
Forms from solutions of dissolved minerals and water
Some of this dissolved material eventually crystallizes and forms the minerals that make up chemical sedimentary rock
Composition of Sedimentary Rock
Organic Sedimentary Rock Forms from the fossils of animals or plants Fossiliferous limestone: animal remains that
eventually become cemented together Made from:
Coral Clams Oysters
Coal: forms underground when partially decomposed plant material is buried beneath sediment and is changed into coal by increasing heat and pressure over millions of years
Sedimentary Rock Structures Stratification: the process in which
sedimentary rocks are arranged in layers Sedimentary rocks sometimes record the
motion of wind and water waves Ripple marks Mud cracks
Indicate the location of an ancient lake, stream, or ocean shoreline
Even rain drop impressions can be preserved
Sedimentary Rock Impressions
Section 4
Metamorphic Rock
Origins of Metamorphic Rock
Rocks in which the structure, texture, or composition of the rock have changed Metamorphosis= changed shape
Most metamorphosis takes place from 50°C to 1,000°C Some take place at more than 1,000°C
Most metamorphosis takes place at depths greater than 2 km This pressure can cause the mineral grains in
rock to align themselves in certain directions
Origins of Metamorphic Rock
Contact Metamorphism Occurs near igneous intrusions Occurs because of magma heating the rock
around it as it moves Regional Metamorphism
When pressure builds up in rock that is buried deep below other rock formations or when large pieces of Earth’s crust collide with each other
Occurs over thousands of cubic kilometers Rocks that have undergone this are found
beneath most continental rock formations
Origins of Metamorphic Rock
Composition of Metamorphic Rock Index minerals: metamorphic minerals that
form only at certain temperatures and pressures Examples:
Biotite Mica Chlorite Garnet Kyanite Muscovite mica Sillimanite Staurolite
Textures of Metamorphic Rock All metamorphic rock has one of two
textures—foliated or nonfoliated
Textures of Metamorphic Rock Foliated Metamorphic Rock
Foliated: the texture of metamorphic rock in which the mineral grains are arranged in planes or bands
Slate: when shale is exposed to slight heat and pressure, the clay minerals change into mica minerals
Textures of Metamorphic Rock Nonfoliated Metamorphic Rock
Nonfoliated: the texture of metamorphic rock in which the mineral grains are not arranged in planes or bands
Commonly made of one or only a few minerals
Recrystallization: the crystals of these minerals may change in size or the mineral may change in composition
Metamorphic Rock Structures
Deformation: a change in the shape of a rock caused by a force placed on it These forces may
cause a rock to be squeezed or stretched. Folds Bends