3 types of rocks
3 types of rocks
• There are 3 types of
rocks found on Earth:
– Igneous
– Sedimentary
– Metamorphic
• Knowing the differences
between these 3 types
of rocks allows us to
learn about Earth’s past.
Igneous Rocks - Formation
• Igneous Rocks are
formed by melting,
cooling, and
crystallization of other
rocks.
• Igneous rocks form as a
result of volcanic
activity, hot spots, and
melting that occurs in
the mantle.
Igneous rocks
• Igneous rocks are common along plate
boundaries or mantle hot spots
Igneous Rocks - Classification
• Igneous rocks are classified
using their texture in the
following ways:
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Glassy
Aphanitic (no visible crystals)
Phaneritic (visible crystals)
Porphyritic (Some visible and
some not visible crystals)
Igneous Rocks - Texture
• Crystal size is used to
classify igneous rocks.
• Crystals form as the
rock cools, and the
crystal size can tell us a
lot about its cooling
history:
– The larger the crystals,
the slower it cooled.
Igneous Rocks - Texture
• Glassy igneous rocks
have no crystal
structure, and probably
formed by very rapid
cooling (such as on the
surface of a lava, or
when a lava enters the
water.)
Igneous Rocks - Texture
• Aphanitic rocks have no
visible crystals, and
probably formed by fast
cooling above ground.
Igneous Rocks - Texture
• Phaneritic rocks have
visible crystals, and
probably formed by
slow cooling below
ground.
Igneous Rocks - Texture
• Porphyritic rocks have
both visible and
nonvisible crystals, and
probably formed by two
different cooling events.
Igneous Rocks - Classification
• Dark igneous rocks are
formed from basaltic or
mafic magma. (Mafic
because it contains a lot
of magnesium and iron).
• The magma that forms
these rocks is usually very
hot (around 1000°C) and
viscous (about the same
viscosity as ketchup.)
Igneous Rocks - Classification
• Light colored igneous
rocks are formed from
silicic (high silica content)
or felsic magmas.
• The magmas that form
these rocks is usually
more cool, (lower than
850°C), and more viscous
(about the viscosity of
peanut butter.)
Igneous rocks - Formations
• Structures and
formations seen
in igneous rocks
include:
– Hexagonal
columnar joints
– Pahoehoe lava
flows
– Dikes, sills, and
batholiths
(plutons)
– Pillow basalts
– Volcanoes
Igneous Rocks - Examples
• The most common
types of igneous rocks
include:
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Rhyolite
Andesite
Basalt
Granite
Diorite
Gabbro
Igneous rocks charted
Igneous rocks - Story
• What do you know
about the history of the
Earth in the place
where this rock was
found?
Sedimentary Rocks - Formation
• Sedimentary rocks are
formed by weathering,
erosion, deposition,
compaction, and
cementation of other
rocks.
• Sedimentary rocks form
in areas where water,
wind, or gravity deposit
sediments.
Sedimentary rocks - formation
• Sedimentary rocks are
likely to form in areas
such as:
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Deltas
Beaches
Rivers
Glaciers
Sand dunes
Shallow seas
Deep oceans
Sedimentary rocks - Classification
• Sedimentary rocks are
classified into two
groups:
– Clastic rocks
– Chemically formed rocks
Sedimentary rocks – Classification
• Sedimentary rocks are
Clastic if they are made
of pieces of other rocks
that have been
weathered and eroded.
• Clastic rocks are
grouped based on the
size of grain that they
are made from.
Sedimentary rocks - Classification
• Very small particles
make up mudrock.
• Medium sized particles
make up sandstone.
• Large particles make up
conglomerates.
Sedimentary rocks - Classification
• Sedimentary rocks that
form from chemical
processes are called
biochemical rocks
(formed from living
things) or Chemical
precipitates (formed
from lakes or shallow
seas.)
Sedimentary rocks - formations
• Structures and
formations seen in
sedimentary rocks
include:
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Stratification
Cross bedding
Graded bedding
Ripple marks
Mud cracks
Fossils
Sedimentary rocks - Examples
• Some of the most
common types of
sedimentary rocks
include:
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Conglomerate
Sandstone
Shale
Limestone
Gypsum
Oolites
Chert (including black
flint and red jasper)
Sedimentary rocks - Story
• What do you know
about the history of the
Earth in the place
where this rock was
found?
Metamorphic rocks - Formation
• Metamorphic rocks are
formed by heat and
pressure changing one
type of rock into
another type of rock.
• Metamorphic rocks
form near lava
intrusions, at plate
subduction zones, and
in deep mountain
roots.
Metamorphic rocks - Formation
• Lava intrusions can
provide heat that
causes metamorphic
rocks to form. These
small areas of
metamorphic rock form
from contact
metamorphosis.
Metamorphic rocks - Formation
• Rocks that
metamorphose
because of increasing
heat and pressure
found at plate
subduction zones and
in deep mountain
roots form large areas
of metamorphic rock
through regional
metamorphosis.
Metamorphic rocks - Classification
• Metamorphic rocks are
classified into 2 major
groups:
– Foliated
– Nonfoliated
Metamorphic rocks - Classification
• Foliated rocks form when
differential pressure causes
minerals to form in layers.
• These rocks will have
stripes or planes that they
will break easily along.
• These “stripes” don’t
usually line up with the
original bedding planes in
sedimentary rocks.
Metamorphic rocks
• Nonfoliated
metamorphic rocks
formed in areas where
the pressure from all
sides was equal, so
there is no “linear”
quality to the rocks.
Metamorphic rocks - Formations
• Structures and
formations seen in
metamorphic rocks
include:
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Folding
Plastic deformation
Stretching
Alternating dark and
light layers (gneissic
foliation)
Metamorphic rocks - Examples
• Some common types of
metamorphic rock
include:
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Slate
Schist
Gneiss
Amphibolite
Marble
Quartzite
Metaconglomerate
Metamorphic rocks - Charted
Metamorphic rocks - story
• What do you know
about the history of the
Earth in the place
where this rock was
found?