Download 3_Types of Rocks

Chapter 10
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Magma is melted rock found below Earth’s
crust.
When magma breaks through Earth’s crust, in
the form of a volcanic eruption, it is called
lava.
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Rocks are made up of minerals.
Scientists have grouped rocks into three (3) major
families (or types):
1. Igneous
2. Sedimentary
3. Metamorphic
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We can usually identify each group by its appearance.
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Igneous rock forms when hot magma and
when hot lava cool and harden.
Geologists (scientists who study rocks)
classify igneous rock based on whether it was
formed above or below Earth’s surface.
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Magma can cool and harden below Earth’s
surface, without ever breaking through it.
The rock that forms as a result is called
intrusive rock.
Rock that forms once lava has cooled off is
called extrusive rock.
Igneous rock occurs mostly below Earth’s
surface.
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Sedimentary rock is made up of sediment.
Sediment includes different types of loose
materials: bits of rock, minerals, and plant
and animal remains.
These sediments become closely packed and
cemented together.
Sedimentary rock makes up about 75% of all
the rock we can see on Earth’s surface.
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Sedimentary rock is usually formed in lakes
and oceans.
Sediment eventually settles, and, over the
years, it starts to pile up.
As sediment slowly settles on top of other
sediment, the rock takes on a layered
appearance. These layers are called beds.
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Each bed (layer) is squeezed together by the
weight of other sediment and the water on
top of it.
This process is called compaction.
In some rocks, minerals dissolve as the water
soaks into the rock, forming a natural cement
that sticks the larger pieces of sediment
together.
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Once a rock is made, it is still possible for it
to change form or shape.
When existing rock is changed into another
type of rock by extreme heat and/or
pressure, metamorphic rock is formed.
The original rock is referred to as the “parent
rock”.
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Metamorphic rock can change so completely
that it no longer looks like the parent rock.
They have, however, enough characteristics in
common that geologists know the two rocks
are related.