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ROCKS
ROCKS
These rocks are at the bottom of the Grand Canyon and
are very old. They have certain characteristics that allow
geologists to identify exactly what type of rock they are.
All rocks do not look the same.
Geologists use the different
characteristics of rocks to
categorize the different
rock types on Earth.
WHAT IS A ROCK?
A geologist can tell how a rock was formed just by
looking at it!!
Rock: A naturally occurring solid mixture composed
of minerals, smaller rock fragments, organic matter
or glass.
Grains: The individual particles in a rock.
WHAT IS A ROCK?
These two rocks mostly contain quartz. They look
different because they formed in different ways.
• Both rocks are made of mineral grains.
• The arrangement of the grains give clues to how the
rocks formed.
CLASSIFYING ROCKS
Three major types of rocks:
• Igneous
Metamorphic
Sedimentary
CLASSIFYING ROCKS: IGNEOUS
ROCKS
Igneous Rocks: Most abundant rocks on Earth.
• Most form deep below Earth’s surface
• All form in a similar way
Formation of Igneous Rocks
As magma or lava cools, mineral crystals begin to form,
which are the grains of new igneous rock.
Magma: Molten rock inside Earth.
Lava: Molten rock that erupts onto Earth’s surface (outside Earth).
CLASSIFYING ROCKS:
IGNEOUS ROCK
Igneous Rock
**Magma is the source for Igneous rocks.
Texture and Composition are used to classify Igneous
rocks.
Minerals from magma and lava form the grains of a
new igneous rock.
Texture: Grain size and how the grains are arranged
in rocks.
CLASSIFYING ROCKS:
IGNEOUS ROCKS
Lava at Earth’s surface cools
quickly, so crystals do NOT have
much time to grow in size.
Geologist describe the texture
of igneous rocks with small
crystals as fine-grained.
CLASSIFYING ROCKS:
IGNEOUS ROCKS
Deep below Earth’s surface, magma
cools slowly, the crystals have more
time to grow.
Geologist describe the texture of
igneous rocks with large crystals
as coarse-grained.
CLASSIFYING ROCKS:
SEDIMENTARY ROCKS
Sediment: Rock and mineral fragments that are
loose or suspended in water.
**Sediments is the source material for
Sedimentary Rock
Formation of Sedimentary Rocks
Lithification: The process through which sediment
turns into rock.
CLASSIFYING ROCKS:
METAMORPHIC ROCKS
Extreme high temperatures and pressure can cause
change in rocks.
Parent Rock: Original rock
New rock formed is called Metamorphic Rock
Metamorphic Rocks: Form when
parent rocks are squeezed,
heated, or exposed to hot fluids.
CLASSIFYING ROCKS:
METAMORPHIC ROCKS
• The parent rock DOES NOT melt – they remain
solid – texture and, sometimes, mineral composition
of the parent rock change.
Two main textures of Metamorphic Rocks:
• Foliated Metamorphic Rock
• Nonfoliated Metamorphic Rock
CLASSIFYING ROCKS:
METAMORPHIC ROCKS
Foliation: Uneven pressures causing flat minerals to
line up, giving the rock a layered appearance.
Nonfoliation: Rocks do not have a layered texture.
** Foliation is the most obvious characteristic of
metamorphic rocks**
ROCKS IN EVERYDAY LIFE
Rocks are abundant natural resources that are used
in many ways based on their physical characteristics.
Some Igneous rocks are hard and durable... Ex.
Granite – Some Igneous rocks is soft but contain
small pieces of hard glass, which makes it useful for
polishing and cleaning… Ex. Pumice.
ROCKS IN EVERYDAY LIFE
Natural layering makes sedimentary rock a highquality building stone.
Ex. Sandstone and limestone are used in
buildings.
Limestone is also used in cement.
ROCKS IN EVERYDAY LIFE