Classification of Rocks

Rocks
Rock
Earth is a solid rock to a depth of 2,900 kilometers,

where mantle meets the liquid outer core.
A rock is a naturally occurring solid aggregate of one or
more minerals.
The aggregate minerals forming the rocks are held
together by chemical bonds.
Petrology is the scientific study of rocks.
Petrologists classify rocks based on how they were

formed.
The Rock
Rocks
 Rocks are any solid mass of mineral or
mineral-like matter occurring naturally
as part of our planet.
 Types of Rocks
1. Igneous rock is formed by the crystallization
of molten magma.
3.2 Igneous Rocks
Formation of Igneous Rocks

1. Intrusive igneous rocks are formed
when magma hardens beneath Earth’s
surface.
2. Extrusive igneous rocks are formed
when lava hardens.
3.2 Igneous Rocks
Classification of Igneous Rocks

 Igneous rocks can be classified based
on their composition and texture.
1. Texture
• Coarse-grained texture is caused by slow
cooling resulting in larger crystals.
• Fine-grained texture is caused by rapid
cooling resulting in smaller, interconnected
mineral grains.
Course-Grained Igneous Texture
Fine-Grained Igneous Texture
3.2 Igneous Rocks

1. Texture (continued)
• Glassy texture is caused by very rapid cooling.
• Porphyritic texture is caused by different rates
of cooling resulting in varied sized minerals.
2. Composition
• Granitic composition rocks are made mostly
of light-colored quartz and feldspar.
Obsidian Exhibits a Glassy Texture.
Porphyritic Igneous Texture
3.2 Igneous Rocks

2. Composition (continued)
• Basaltic composition rocks are made mostly
of dark-colored silicate minerals and
plagioclase feldspar.
• Andesitic composition rocks are between
granitic light-color minerals and basaltic
composition dark-colored minerals.
• Ultramafic composition rocks are made mostly
from iron and magnesium-rich minerals.
Basalt
The Rock Cycle
The Rock
Rocks
 Types of Rocks
2. Sedimentary rock is formed from the
weathered products of preexisting rocks that
have been transported, deposited, compacted,
and cemented.
3.3 Sedimentary Rocks
Formation of Sedimentary Rocks

 Weathering, Erosion, and Deposition
• Erosion involves the weathering and the
removal of rock.
• Deposition occurs when an agent of erosion
—water, wind, ice, or gravity—loses energy
and drops sediments.
Formation of Sedimentary Rocks

 Compaction and Cementation
• Compaction is a process that squeezes, or
compacts, sediments.
• Cementation takes place when dissolved
minerals are deposited in the tiny spaces
among the sediments.
Classification of Sedimentary Rocks

 Two Main Groups
1. Clastic sedimentary rocks are composed
of weathered bits of rocks and minerals.
• Classified by particle size
• Common rocks include
- Shale (most abundant)
- Sandstone
- Conglomerate
Shale with Plant Fossils
Conglomerate
Classification of Sedimentary Rocks

 Two Main Groups
2. Chemical sedimentary rocks form when
dissolved substances precipitate, or separate,
from water.
• Common rocks include
- limestone—most abundant chemical rock
- microcrystalline quartz known as chert, flint,
jasper, or agate
- evaporites such as rock salt or gypsum
- coal
Fossiliferous Limestone
Classification of
Sedimentary Rocks
Features of Some Sedimentary Rocks

 Features of sedimentary rocks are clues
to how and where the rocks are formed
The Rock
The Rock
Rocks
 Types of Rocks
Metamorphic - forms from pre-existing rocks:
either metamorphic, igneous, sedimentary or
other metamorphic rocks that have been
altered by agents ofmetamorphism.
Examples: quartzite, marble, slate, phyllite
Metamorphism - transformation of one rock type
into another.
3.4 Metamorphic Rocks
Formation of Metamorphic Rocks

 Metamorphism means “to change
form.”
 Most metamorphic changes occur at
elevated temperatures and pressures.
 Conditions for formation are found a few
kilometers below the Earth’s surface and
extend into the upper mantle.

 Contact metamorphism occurs when
magma moves into rock.
• Occurs near a body of magma
• Changes are driven by a rise in temperature.

 Regional metamorphism results in
large-scale deformation and high-grade
metamorphism.
• Directed pressures and high temperatures
occur during mountain building.
• Produces the greatest volume of metamorphic
rock
Agents of Metamorphism
 Heat
• Provides the energy needed to drive chemical
reactions
 Pressure
• Causes a more compact rock with greater
density
Origin of Pressure in
Metamorphism
Agents of Metamorphism
 Hydrothermal Solutions
• Hot water-based solutions escaping from the
mass of magma
• Promote recrystallization by dissolving original
minerals and then depositing new ones
Classification of Metamorphic Rocks

 Two main categories
1. Foliated Metamorphic Rock
• Has a banded or layered appearance
2. Nonfoliated Metamorphic Rock
• Does not have a banded texture
Classification of
Metamorphic Rocks
Gneiss Typically Displays a
Banded Appearance
Marble—A Nonfoliated
Metamorphic Rock
The Rock
Metamorphic - forms from pre-existing rocks: either

metamorphic, igneous, sedimentary or other
metamorphic rocks that have been altered by
agents ofmetamorphism.
Examples: quartzite, marble, slate, phyllite
Metamorphism - transformation of one rock type into
another.
The Rock
2 types of metamorphism
1. Regional-due to changes in pressure and
temperature over large region of the crust. It
may happen when rock is buried deep
below the surface of the earth.
2. Contact-the rock minerals and textures are
changed mainly by heat due to contact with
magma.
The Rock
2 types of metamorphism
1. Regional-due to changes in pressure and
temperature over large region of the crust. It
may happen when rock is buried deep
below the surface of the earth.
2. Contact-the rock minerals and textures are
changed mainly by heat due to contact with
magma.
The Rock
Classification:
1.Texture - refers to the size arrangement and grains within the rock.
Foliation - any planar arrangement of mineral grains or

structural features within the rock.
a. Foliated rocks – can be arranged in terms of increasing

metamorphism, and it appeared layered or banded with compressed
mineral grains. Example: mica
b. Non-foliated rocks – usually made up of only few minerals.

3.1 The Rock Cycle
The Rock Cycle

 Shows the interrelationships among the three
rock types (igneous, sedimentary, and
metamorphic)
 Magma is molten material that forms deep
beneath the Earth’s surface.
 Lava is magma that reaches the surface.
 Weathering is a process in which rocks are
broken down by water, air, and living things.
 Sediment is weathered pieces of Earth
elements.
The Rock Cycle
3.1 The Rock Cycle
Energy That Drives the Rock Cycle

 Processes driven by heat from the Earth’s
interior are responsible for forming both
igneous rock and metamorphic rock.
 Weathering and the movement of weathered
materials are external processes powered by
energy from the sun.
 External processes produce sedimentary
rocks.

Classification of Rocks

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Rocks

Earth is a solid rock to a depth of 2,900 kilometers,

Petrology is the scientific study of rocks.

Petrologists classify rocks based on how they were

Formation of Igneous Rocks

Classification of Igneous Rocks

Classification of Igneous Rocks

Classification of Igneous Rocks

Formation of Sedimentary Rocks

Formation of Sedimentary Rocks

Classification of Sedimentary Rocks

Classification of Sedimentary Rocks

Features of Some Sedimentary Rocks

Formation of Metamorphic Rocks

Formation of Metamorphic Rocks

Formation of Metamorphic Rocks

Classification of Metamorphic Rocks

Metamorphic - forms from pre-existing rocks: either

Foliation - any planar arrangement of mineral grains or

a. Foliated rocks – can be arranged in terms of increasing

b. Non-foliated rocks – usually made up of only few minerals.

The Rock Cycle

Energy That Drives the Rock Cycle

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