How Earth’s
Rocks Were
Formed
I. UniformitarianismUniformitarianismJames Hutton’s 22-part theory states:
A. The geologic processes now at work
were also active in the past
B. The present physical features of Earth
were formed by these processes
gradually
*Earthquakes don’t happen because
God is mad at us!
II. 3 types of Rocks
Igneous
Sedimentary
Metamorphic
A. Igneous
Igneous-- are formed by the cooling of
magma or lava
1. 2 types of igneous rocks
a. Plutonic (intrusive)(intrusive)-form underground
from cooled magma
Ex: granite
b. Volcanic (extrusive)(extrusive)- form
when lava cools
Ex: obsidian
2. Two different types of magma or lava
a. felsicfelsic1. high silica
2. low Ca, Fe, Mg
3. plutonic rocks
b. MaficMafic1. low silica
2. high Ca, Fe, Mg
3. volcanic rocks
3. Textures of igneous rocks are
determined by size and shape of
crystals.
a. Hardens quickly small or no crystals
Ex: obsidian
b. Thick magma that hardens slowly large
crystals
Ex: granite
c. Porphyry
Porphyry-- 2 textures in 1 rock. Large
crystals surrounded by a finefine-grained rock
mass.
Porphyritic texture - a
mixture of coarse and fine
grained textures in the same
rock - indicates different
cooling rates.
Geode
Almost round
amethyst
geode table.
18 inches tall,
27 to 28
inches in
diameter.
$3,999.99
B. Sedimentary RocksRocks- form when
sediments cement togethertogether-3 types
1. Clastic Sedimentary rockrock-form from
fragments of other rocks
a. Water is the main agent for
weathering, but it also contains
natural cements (silicate, calcite &
rust)
b. Pressure from overlying sediments
can cause sediments to stick
together.
b. Water moves and drops sediments
according to size
1. Large pebbles and gravel are in shallow regions
regions
conglomerate
2. Intermediate regions have sand sandstone
a. sandstone is made of quartz and is porous &
permeable
Don’t throw
sandstone in a
campfire!!!
3. Deep, calm regions have silt and clay
clay shale
a. shale is smooth, soft & impermeable
2. Chemical sedimentary rockrock- formed
when minerals fall out of water solutions
and form chemical sediments. These
are cemented together.
a. examples: limestone, rock salt
Limestone is made from the
calcite which came from the
beds of evaporated seas
and lakes and from sea
animal shells. It is used in
concrete.
3. Organic sedimentary rocksrocks- come from
the remains of animals & plants
Example: Limestone from shellshellproducing organisms like clams &
oysters
4. Stratification
Stratification-- sedimentary rocks are
arrange in visible layers
5. Fossils are trapped in sedimentary
rocks only!!!
a. Why? The heat or pressure needed
to form other types of rock would
destroy the fossil.
b. Fossil
Fossil-- remains, impressions, or any
other evidence of plants & animals
preserved in rock
C. Metamorphic Rock -formed from
existing rock by the action of heat,
pressure, and chemicals. They
form in 2 ways:
1. Regional metamorphism – when
large areas are under intense heat &
pressure
a. Rocks formed this way are very
dense
b. Examples:
sandstone
sandstone
quartzite
limestone
limestone
marble
c. FoliationFoliation- the flat or wavy sheetsheet-like
layering within some metamorphic rocks
Quartzite is a non-foliated
metamorphic rock
Phyllite is a foliated
metamorphic rock
d. The metamorphism of shale:
Slate
Phyllite
Shale
Gneiss
schist
2. Contact MetamorphismMetamorphism- occurs when
hot magma forces its way into overlying
rock & bakes what it comes in contact
with
a. Changes in rock are less drastic than in
regional
b. No foliation
How is a metamorphic
rock made?
III. The Rock Cycle
A. Rocks are related!!
B. Igneous rock is considered “parent
rock”
Igneous
Melting to become
magma & cooling
Weathering & Erosion
to form sediments that
cement together
Metamorphic
Sedimentary
Heat & Pressure
C.
C.Why
Why is the rock cycle not
as simple as the diagram
would indicate?
Because there are
detours!
Igneous
Melting to become
magma & cooling
Weathering & Erosion
to form sediments that
cement together
Metamorphic
Sedimentary
Heat & Pressure
The End!!!!!!!!
Your written test will be tomorrow & the
practical will be Thursday!