Download Rock Cycle - Ms. Banjavcic`s Science

Rocks and the Rock Cycle
Ch. 4 - pg. 88 – Earth Science
• What is a rock?
– a mixture of minerals, rock fragments, volcanic glass,
organic matter or other natural materials
– How are rocks different from minerals?
• Rock Cycle (p. 91)
– process that creates and changes rocks.
– shows the three main types of rocks and how they are
created.
– shows how rocks can change from one type to another.
• The Rock Cycle shows how each type of rock can change
from processes such as:
– Melting
– Weathering and Erosion
– Compaction and Cementation
– Heat and Pressure
– Cooling
Rock Cycle:
• Sedimentary Rock… with
heat and pressure can
form a Metamorphic Rock.
• Metamorphic Rock…
melts, and later cools, to
from an Igneous Rock.
• Igneous Rock… after
weathering and erosion
into sediments, which can
then solidify into a
Sedimentary Rock.
• Igneous Rock… with heat
and pressure can also
become a Metamorphic
Rock.
• Igneous Rock: formed from cooling magma that hardens.
These are the most common rocks on Earth.
– Magma is formed from heat deep below Earth’s surface.
As it becomes hotter, it rises towards the surface. As
magma reaches the Earth’s surface, it is called lava.
• Intrusive igneous rocks – rocks that form from
magma BELOW the Earth's surface.
– These are found at the surface only after the layers
of rock and soil that once covered them have been
removed by erosion.
– These take a long time to cool which produces
mineral grains that are large enough to see with an
unaided eye.
• Extrusive igneous rocks – rocks that are formed as
lava cools ON the surface of the Earth.
– Lava cools quickly once it reaches the surface. The
quick cooling rate keeps mineral grains from
growing large. Therefore, these rocks are fine
grained.
– Pg. 96
Classifying Igneous Rocks:
• Igneous rocks are formed by different types of magma (or lava)
– Basaltic Rocks – Igneous rocks which are dense, dark
colored rocks.
• They form from magma that is rich in iron and magnesium.
• This lava flows from volcanoes in Hawaii
– How does this explain the black beach sand common in
Hawaii?
– Granitic Rocks – Igneous rocks are light-colored rocks of
lower density than basaltic rocks.
• This magma is thick and stiff and contains a lot of silica but
lesser amounts of iron and magnesium.
– Andesitic Rocks – igneous rocks that have mineral
compositions between those of basaltic and granitic rocks.
• Many volcanoes around the rim of the Pacific Ocean form
andesitic magma.
• Metamorphic Rock: rocks that have
changed because of changes in
temperature and pressure or the
presence of hot, watery fluids.
– Below the Earth’s surface there is a high
amount of pressure from the layers
above them. This pressure causes the
formation of metamorphic rock. (Read
Pg. 100)
– Can be changed in the form of the rock,
the composition of the rock, or both.
– Can form from igneous, sedimentary or
other metamorphic rocks.
Classifying Metamorphic
Rocks:
• Foliated Rocks – when
mineral grains line up in
parallel layers.
– Slate and gneiss
– Read pg. 101
• Nonfoliated Rocks – when
mineral grains grow and
rearrange, but do not form
layers.
– Sandstone and marble
– Read pg. 102
• Sedimentary
Rock: formed when
sediments are pressed and
cemented together, or when
minerals form from solution. 75% of
the rocks exposed at the surface are
sedimentary rocks.
– These often form in layers. This
can be very valuable when
trying to find the age of
rocks...the older layers are on
the bottom because they were
deposited first.
Classifying Sedimentary Rocks
• Detrital Sedimentary Rocks – made from broken fragments of
rocks. Caused by the following processes...
– Weathering and Erosion – the breakdown of rocks into smaller
pieces when they are exposed to air, water, or ice. The rock is
unstable and breaks down chemically and mechanically.
– Compaction – the process that forms sedimentary rocks when
layers of sediments are compressed by the weight of layers
above them.
– Cementation – the process in which sediment grains are held
together by natural cements that are produced when water
moves through rock and soil.
– Detrital rocks have granular textures, much like granulated
sugar. They are named according to the shapes and sizes of
the sediments that form them.
– Often contain the minerals quartz and feldspar.
Classifying sedimentary rocks continued...
• Chemical Sedimentary Rocks – these form when
dissolved minerals come out of solution.
– This forms sediments which eventually turn into
rocks.
– They are not made from pieces of preexisting rocks.
» Limestone
» Made from calcium carbonate which is carried in
ocean water.
» Rock Salt
» Forms from water that is rich in salt – halite. (pg.
107)
Classifying Sedimentary Rocks continued....
•Organic Sedimentary Rocks – rocks that are made from
once-living things.
» Fossil-rich limestone – animals such as mussels, clams,
corals and snails make their shells from calcium
carbonate. When they die, shells accumulate on the
ocean floor. When these shells are cemented together,
this type of limestone forms.
» Chalk – when you write with “naturally occurring” chalk,
you're crushing and smearing the calcite-shell remains of
once-living ocean organisms.
» Coal – forms when pieces of dead plants are buried
under other sediments in swamps. These plant materials
are chemically changed by microorganisms. These
sediments are compacted over millions of years to form
coal, an important source of energy. (pg. 108)