ROCK ON
“ The present is the key to the
past.”
-James Hutton
The Rock Cycle explains
how Rock and Natural Processes
are related
weathering
Sedimentary Metamorphic
Igneous
The Rock Cycle involves the
recognition of three main classes
of rocks. All three types are
found in Michigan.
The three rock types are …
Sedimentary
CEMETERY Metamorphic
METABOLIC
Rocks Rocks
Igneous
INGENIOUS
Rocks Right?
The mantle, crust and surface of the earth
can be thought of as a giant recycling machine;
rocks are neither created nor destroyed,
but redistributed and transformed from
one rock type to another.
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There is a hierarchy to the
Atoms make up elements.
elements of Geology
Elements combine to form
the natural compounds.
Natural compounds
and elements form
minerals.
.
Minerals make up rocks.
Rocks make up the Earth.
IGNEOUS ROCKS
Igneous Rocks
1. All rocks that
form from a molten
state.
2. Surface rocks-
from molten lava
are called
extrusive
(volcanic).
3. Rocks from
molten material far
beneath surface-
intrusive.
Magma
Felsic, (slow, thick),
high percent of silica
(acidic),forms light
colored rocks - granite.
Mafic, ( hotter and
more fluid), low
percent of silica, high
percentage of iron,
magnesium and
calcium, forms dark
colored (basic) rocks
like basalt.
Texture of Ignous Rocks -
Phaneritic Texture
Texture of Igneous
Rocks- depends upon
rate of cooling and
solidification.
Phaneritic textured
rocks are comprised of
large crystals that are
clearly visible to the
eye with or without a
hand lens or binocular
microscope. Ex.
Granite
Rapid Cooling-Aphanitic
Texture
Aphanitic texture
consists of small
crystals that cannot be
seen by the eye with or
hand lens.
Magmas that cool on
the surface harden
rapidly, forming tiny
crystals and are fine-
grained, like basalt.
Porphyritic Texture
Porphyritic
rocks are
composed of at
least two
minerals having
a conspicuous
(large) difference
in grain size
Slow Cooling
Slow rate- larger
crystal growth and a
grainier texture.
Are formed below the
Surface-cools and
solidifies slowly, large
mineral grains of fairly
uniform size: coarse-
grained, like granite.
Very Fast Cooling
Glassy Texture-
Quickly harden
smooth as glass,
Ex. obsidian.
SEDIMENTARY ROCKS
Sedimentary Rocks
Formed when layers of sediment are
deposited by water and cemented
together through a process called
lithification.
Cement -silica, lime, or iron
precipitates that form in the pore
spaces of the sediments.
Sedimentary Rock
Classification- Clastic Origin
Clastic
sedimentary
rocks are
formed from
bits and pieces
of other rocks.
(sandstone)
Shale
Made from very
fine particles,
silt, like clay.
Need a
magnifying glass
to see grains.
Sandstone
Formed from grains
of weathered rock.
Texture is visable
to the naked eye.
Soft- can usually
scrape grains off
with fingernail.
Conglomerate
Made from pebble-
sized rocks, or
larger.
Easily seen with
the naked eye.
Sedimentary Rock
Classification- Chemical
Chemical
sedimentary rocks are
formed by chemical
activity -precipitation
in fresh or seawater,
are fine-textured. Ex.
Salt
Chert - flint
Chemical Sedimentation:
Geodes
Sedimentary Rock
Classification- Organic
Organic sedimentary
rocks form from
remains of plants or
animals. Fossils can
be seen.
Fossiliferous
Limestone
Coal Series
Peat -Decaying
plants and animals
in a bog
Lignite- soft, burns
poorly
Bituminous- harder,
still not efficient
Anthracite-hardest,
burns best
Fossil Trilobite
Formed in shale.
Fossil Fish
Embedded in
sandstone.
Petrified Wood
SiO2 precipitates
from water,
replacing the
organic tissue.
Petrified forest in
Alaska
Petrified wood in
Arizona
METAMORPHIC ROCKS
Metamorphic Rocks
1. Existing rocks 2. During this time
are changed by the atoms of the
heat, pressure, and original minerals
solution deep are rearranged to
within the earth form new
and over long materials.
periods of time.
Types of Metamorphism
Contact Metamorphism -when magma comes in contact
with an already existing body of rock. When this happens
the existing rock’s temperature rises and also becomes
infiltrated with fluid from the magma.
Regional Metamorphism occurs over a much larger area.
Regional metamorphism is caused by large geologic
processes such as mountain-building. Regional
metamorphism usually produces foliated rocks such as
gneiss and schist.
Dynamic Metamorphism also occurs because of
mountain-building. These huge forces of heat and pressure
cause the rocks to be bent, folded, crushed, flattened, and
sheared.
Paths to Formation
Clay-Shale-Slate-Schist
Sand-Sandstone-Quartzite-Phyllite-Schist
Granite-Gneiss-Schist
Limestone-Marble
Metamorphic Rock Texture
Foliated (or banded) -
layered appearance,
crystals line up in
parallel rows-gneiss
(from granite)
Foliated Texture
A->B->C->D->-E>-F
A. Sandstone
(unmetamorphosed)
B. Slate-LOWEST GRADE
C. Phyllite
D. Schist
E. Gneiss-HIGHEST GRADE
F. Migmatite (melting of
gneiss
Nonfoliated Texture
Nonfoliated -
generally
massive with no
apparent layering-
quartzite (from
sandstone)
Marble, from
limestone
Rock Cycle
Rock Cycle
In Michigan,
Igneous and
igneous and Metamorphic
metamorphic rocks
rocks make up the
bedrock in the
western northern
Sedimentary
peninsula. rocks
Sedimentary rocks Generalized
make up the lower Bedrock Geology
of Michigan
peninsula.
DEQ GSD - The Rock Cycle in Michigan - February 2001
THE END