Download Igneous Rocks

Igneous Rocks
Igneous Rocks
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Igneous rocks are
any rock that
forms from
magma or lava.
Igneous rocks
may form on or
beneath Earth’s
surface.
Classifying Igneous Rocks
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The name igneous comes from the latin word
ignis, meaning “fire”.
Igneous rocks are classified according to their
origin, texture, and mineral classification.
There are two types of igneous rock
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Extrusive
Intrusive
Origin
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Extrusive igneous rocks
are formed when lava
erupts or flows above
the Earth’s surface and
cools forming a rock
Quick cooling makes
rocks with very little
mineral crystals.
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Basalt is the most
common extrusive rock
Origin
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Intrusive igneous rocks forms when magma hardens
beneath the Earth’s Crust.
The cooling can take thousands or even millions of years,
mineral crystals can grow quite large if space allows
•
Granite is the most abundant intrusive rock on Earth’s continents
Texture
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Depends on the size and shape of the mineral
crystals
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An exception to this rule are certain types of rock that
have a texture like glass.
Igneous rocks may have similar chemical
compositions and yet be very different
Mineral Composition
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Light colored rocks
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Most of Earth’s minerals
contain silica
Magma high in silica
usually forms light-colored
rocks
Granite ranges in color:
light gray, red, pink, or
nearly black.
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Dark colored rocks
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Magma with a low
silica content usually
forms dark-colored
rocks.
Basalt has low silica
content and also
contains other darkcolored minerals
Uses of Igneous Rocks
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Building materials
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More than 3,500 years ago ancient Egyptians used
granite for statues
About 600 years ago the Incas of Peru used
granite and other igneous
U.S. granite is widely used to build bridges, public
buildings, paving streets, counter tops etc…
Tools
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Obsidian was used by ancient native Americans for
sharp tools for cutting and scraping.
Sedimentary Rocks
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Stay tuned
for another
exciting day
of notes
when we
discuss
weathering
and the
formation of
sedimentary
rock.