Download IGNEOUS ROCKS MAGMA SEDIMENTS SEDIMENTARY ROCKS

Earth Science Notes
Chapter Four-Rocks: Mineral Mixtures
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SECTION 1-Understanding Rock [Petrology]
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1. What is a rock? A rock is a solid mixture of minerals and/or organic materials. Example-granite (a type of
igneous rock) is made up of a mixture of quartz, feldspar, and mica.
2. Rocks are classified into three main types-igneous, sedimentary , and metamorphic-depending on how they
formed.
3. The rock cycle is a series of natural processes by which rocks are slowly changed from one kind of rock to
another kind of rock. Rocks change slowly both inside the Earth and at the Earth’s surface.
4. Rock Cycle Diagram:
IGNEOUS
ROCKS
Melting
Weathering and
Erosion
Cooling
MAGMA
Melting
Heat and
Pressure
SEDIMENTS
Weathering
and Erosion
Weathering
and Erosion
Compaction
and
cementation
SEDIMENTARY ROCKS
METAMORPHIC ROCKS
Heat and Pressure
5. Rocks changed by the following natural processes:
a. Weathering-breakdown of rock into smaller pieces by mechanical or chemical means.
b. Erosion-the removal and transport of material by wind, water, or ice.
c. Compaction-a process that occurs when layers of sediment become compressed by the weight of
layers above them.
d. Cementation-process in which sediments are glued together by minerals deposited between the
sediments.
e. Melting and Cooling
6. Classification of Rocks:
a. The three main types of rocks can be further classified based on composition and texture.
b. Composition-the make-up of a rock; describes either the minerals or elements present in it.
1. Example-the igneous rock granite is made up of the minerals mica, feldspar, and quartz.
c. Texture-the sizes, shapes, and positions of the grains that a rock is made of.
1. Fine-grained-rocks made entirely of small grains. Ex. silt or clay.
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2. Coarse-grained-rocks that are made of large grains, such as pebbles. Ex. conglomerate
3. Medium-grained-rocks that have a texture between fine and coarse-grained. Ex. sandstone.
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SECTION 2-Igneous Rock [rock from “fire”]
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1. Igneous rock is formed from hot, molten liquid materials that cool and harden.
2. Two kinds of molten material:
a. Magma-below the Earth’s surface; less dense than surrounding rock, thus rises slowly upward. Made
up mostly of silicon, oxygen, and water vapor.
1. Felsic magma-magma with a high silica content [silicon and oxygen]; it is light colored, thick,
and pasty.
2. Mafic magma-magma with a low silica content; it is dark colored, thin and runny.
b. Lava-molten rock on the Earth’s surface.
3. Magma cools into various types of igneous rock depending on the (1)composition of the magma and (2)the
amount of time it takes the magma to cool and solidify .
4. Two groups of igneous rocks: [Figure 11 page 88]
a. Intrusive-magma cools beneath the Earth’s surface. It cools slowly, thus has large mineral grains. All
intrusive rocks...
1. cooled slowly.
2. have minerals that can be seen without magnification. [large crystals]
3. have a coarse texture.
b. Extrusive-formed when lava cools on the Earth’s surface. Cools quickly, thus have a fine-grained
texture. All extrusive rocks...
1. cooled quickly.
2. have small crystal grains, thus difficult to see individual mineral grains.
3. have a fine texture.
5. Further classification of Igneous Rocks:
a. Can further classify igneous rocks by the type of magma they formed from.
b. Three types of Igneous Rocks:
1. Basaltic-form from mafic magma; flows readily, is thin & runny. [temp. range 900-1200 oC].
Contains a high percent of iron and magnesium; makes these igneous rocks dense and dark
colored.
a. Hawaii-lava is basaltic in nature. Eruptions on these islands are calm.
2. Granitic-form from felsic magma; thick magma that does not flow easily due to high silica
content. [temp. is below 800oC]. Contains high percent of aluminum, potassium, and sodium, thus
rocks are less dense and light colored.
a. Usually associated with violent volcanic eruptions.
3. Andesitic-have mineral compositions between those of granitic and basaltic rocks.
*SEE ROCK TYPE STUDY GUIDE on Igneous Rocks
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SECTION 3-Sedimentary Rock [75% of rocks at Earth’s surface]
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1. These are rocks that are produced by weathering either mechanically or chemically. Weathering is the
breaking down of rock material into small fragments called sediments,
2. Sedimentary rock is formed when sediments [from weathered igneous, metamorphic, and/or other
sedimentary rocks] are compacted and cemented together. [See Figure 15 page 91]
3. Classification of Sedimentary Rock:
*SEE ROCK TYPE STUDY GUIDE on Sedimentary Rocks
a. Three classes of sedimentary rock:
1. Clastic (detrital)Sedimentary Rock-form when fragments of rocks and minerals are
compacted and cemented together. Clastic sed. rocks always have a granular texture.
2. Chemical Sedimentary Rock-come out of solution or are left behind by evaporation. Chemical
sed. rocks generally have a non-granular texture.
3. Organic Sedimentary Rock-are made mostly of the remains of once-living organisms.
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SECTION 4-Metamorphic Rock [rock that has changed shape, texture, or composition]
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1. Metamorphic Rocks-rocks formed as a result of changes in pressure or temp. Form from preexisting
igneous, sedimentary, or other metamorphic rocks.
2. Occur at depths of 12-16 km (7-10 miles) below surface where heat and pressure aren’t quite enough to get
the rocks to melt. [If it melts you have magma which cools to form igneous rocks!]
a. Three changes may occur to a rock that undergoes metamorphism:
1. Rearrangement of mineral grains. [form bands of mineral grains]
2. Enlargement of crystals.
3. Change in chemistry of rock--the elements recombine to form different minerals. See fig. 26
on page 97.
3. Two types of metamorphism:
1. Contact Metamorphism-”baking”--occurs when magma comes in direct contact with rocks. The heat
from the magma can change the structure and mineral composition of the rock.
2. Regional Metamorphism-occurs over an area thousands of square kilometers during periods of
tectonic activity (mountain building).
a. The movement of tectonic plates against each other creates tremendous heat and pressure.
This heat and pressure causes chemical changes in the minerals of the rocks.
b. Most metamorphic rock is formed by this method.
4. Classification of Metamorphic Rocks done by their textures:
*SEE ROCK TYPE STUDY GUIDE on Metamorphic Rocks
a. Foliated Metamorphic Rocks:
1. Rocks are banded; mineral grains flatten and line up in parallel bands.
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b. Nonfoliated Metamorphic Rocks:
1. Metamorphic rocks that lack in true banding.
2. Usually only contain one mineral.
3. All have undergone internal changes, but not visible; mineral grains may change, grow, and
rearrange, but lack bands.
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CHAPTER 4 QUESTIONS TO CONSIDER:
1. Distinguish between a rock and a mineral.
2. Describe how each type of rock changes into another as it moves through the rock cycle.
3. List two characteristics of rock that are used to help classify it.
4. Explain how the cooling rate of magma affects the properties of igneous rock.
5. Distinguish between igneous rock that cools deep within the crust and igneous rock that cools at the surface.
What do petrologist call each igneous rock type?
6. Contrast basaltic, granitic, and andesitic igneous rocks.
7. Explain how sedimentary rocks form from sediments.
8. Describe the process by which clastic sedimentary rock forms. How are sandstone and siltstone different
from one another? How are they the same?
9. Describe two ways that a rock can undergo metamorphism.
10. Describe the difference between foliated and nonfoliated metamorphic rock.
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