Download Metamorphic Rocks - Faustina Academy

+
JMJ












Chapter 4: Rocks
Faustina Academy
Earth Science
Section 1: The Rock Cycle
Most rock used for building contains one or more common minerals such as
quartz, feldspar, mica, or calcite
Rock
 Mixture of minerals, volcanic glass, organic matter, and other materials
(pg. 90)
What is a Rock?
Rock cycle (pg 91-92)
 Three types of rock and the processes that form them

Igneous

Sedimentary

Metamorphic
 No distinct beginning or end to the rock cycle
 Rock can be weathered to small rock and mineral grains, which can be
eroded and carried away by wind, water, or ice
However, chemical elements of minerals and rocks are not destroyed
Illustrates principle of conservation of matter
 Matter is neither created nor destroyed
 Minerals are redistributed to other forms, never destroyed
Discovering the Rock Cycle
James Hutton (1788) first to recognize rocks undergo profound changes
 Noticed rock layers in Siccar Point not neatly stacked
 Some layers tilted and partly eroded
He discovered other evidence of rocks constantly changing
Section 2: Igneous Rocks
Volcanoes eject a flow of molten rock material, called magma
When hot magma cools and hardens, it forms igneous rocks
Igneous Rocks
Most magma comes from deep below Earth's surface

Near the surface to 150km (93 miles)
Temperatures are very hot!

650˚C - 1200˚C (1202˚F - 2192˚F)
Heat that melts rocks comes from within Earth's interior
 Decay of radioactive elements produces heat






Heat remains from formation of the planet, which was originally
molten
Igneous Rocks
Magma is less dense than surrounding solid rock, so forced upwards toward
the surface (pg 95)
Lava
 Magma that reaches Earth's surface and flows from volcanos
Intrusive Rocks
As magma cools, atoms and molecules are rearranged into crystals called
mineral grains
Rocks form as mineral grains grow together
Intrusive rocks

Rocks form from magma below the surface

Found at the surface after layers of rock and soil that once covered
them are removed by erosion

Form deep within the earth, surrounded by other rocks

Long time for them to cool

Produces mineral grains large enough to be observed with unaided eye
Extrusive Rocks


Extrusive rocks

Formed as lava cools on Earth's surface

Lava cools quickly on land

Mineral grains stay small because atoms and molecules don't have time
to arrange into large crystals (pg. 96)
Pumice, obsidian, scoria are examples of volcanic glass




Cooled quickly so few or no mineral grains formed
The atoms aren't arranged in orderly patterns and few
crystals are present
With pumice and scoria, gases become trapped in the
molten material as it cools
Some gases escape and leave holes

•
•
•
Classifying Igneous Rocks
Igneous rocks further classified by the type of magma from which they form
 Basaltic
 Andesitic
 Granitic
Basaltic rocks
–
–
Dense & dark colored
Rich in iron and magnesium (black sand)
Granitic rocks
–
–
–
Light-colored
Lower density than basaltic
High is silica but less Fe and Mg
Andesitic rocks
–
Mineral compositions between those of granitic and basaltic
Common Igneous Rocks
Basaltic:
Basalt (E)
Gabbro (I)
Andesitic:
Andesite (E) Diorite (I)
Granitic:


Granite (I)
Pumice (E)
Igneous Rock Formation
Metamorphic Rocks
Metamorphic rocks
 Rocks affected by temperature and pressure changes
 Form from igneous, sedimentary, or other metamorphic rocks
Metamorphic Rocks
Rocks beneath Earth's surface under great pressure from rock layers above












Temperature also increases with depth
In some places, the conditions ideal for magma formation
Heat and Pressure
In other areas where the rocks don't melt into magma, some mineral grains
can become flattened like a sandwich
Sometimes under great heat or pressure, minerals exchange atoms to form
new, larger minerals
Depending upon the amount of pressure and temperature, one type of rock
can changed into several different metamorphic rocks
Also, each type of metamorphic rock can come from several kinds of parent
rocks
Eg. sedimentary rock shale will change into slate, and with increasing
pressure and heat, turns into phyllite, then schist, then gneiss
Schist can form from basalt, and gneiss can come from granite
Hot Fluids
Fluids can move through solid rock- the fluids are mostly water with
dissolved elements that chemically react with a rock and change its
composition, especially when the fluids are hot
Most fluids that transform rocks during metamorphic processes are hot and
mainly comprised of water and carbon dioxide
Metamorphic rocks form from igneous, sedimentary, or other metamorphic
rocks.
Heat, pressure, and hot fluids trigger the changes
Classifying Metamorphic Rocks


Foliated Rocks
Metamorphic rocks can be classified according to composition and texture
Foliated rocks- produced when mineral grains flatten and line up in parallel
layers




Slate forms from the sedimentary rock shale (pg. 101)
shale minerals arrange in layers to form slate
The minerals in slate are pressed together so tightly that
it's watertight and ideal for pools, patios, roofs
Gneiss forms when granite and other rocks are changed
Quartz, feldspar, mica, and other minerals in gneiss aren't
changed much, but are arranged into bands















Nonfoliated Rocks
In some metamorphic rocks, layering doesn't occur, the minerals just grow
and rearrange- nonfoliated rocks
Sandstone- a sedimentary rock composed mostly of quartz grains- when
sandstone is heated under a lot of pressure, the grains of quartz grow in size
and become interlocking like puzzle pieces, resulting in a rock called
quartzite
Marble forms from the sedimentary rock limestone, which is composed of
he mineral calcite
Usually marble contains other minerals such as hornblende and serpentine
which gives it a black or green color
Marble is popular with sculptors because it's softer than other rocks
Nonfoliated rocks: quartzite, marble foliated: gneiss, slate
•
Sedimentary Rocks
While igneous rocks are the most common rocks on earth, 75% of the rocks
on Earth's surface are sedimentary
Sediments- loose materials such as rock fragments, mineral grains, bits of
shell
Moved around by water, wind, ice, gravity
Sedimentary rocks form when sediments are pressed and cemented
together, or when minerals form from solutions
Stacked Rocks
Sedimentary rocks often form as layers
The oldest layers are on the bottom because they were deposited first
Sometimes, forces within Earth overturn layers of rock and the oldest layers
are no longer on the bottom
Similar to a stack of homework that has accumulated over time- the oldest
papers are on the bottom until the stack is disturbed
Classifying Sedimentary Rocks
Sedimentary rocks can be made of just about any material found in nature



From all three rock types
remains of dead organisms
Sedimentary rocks are classified by their composition and manner in which
they were formed


–








Compaction & Cementation
When rock is exposed to air, water, or ice, it is
unstable and breaks down chemically and mechanically in
a process called weathering
The movement of weathered material is erosion
Compaction & Cementation
If sediments are large (sand, pebbles), pressure alone can't make them stick
together, they must be cemented
Cementation- occurs when water soaks through soil and rock


Detrital rocks are made from broken fragments of other
rocks- these loose sediments are compacted and cemented
together
Erosion moves sediments to a new location, where they are deposited- layer
upon layer of sediment builds up
Pressure from the upper layers pushes down on the lower layers
If the sediments are small, they can stick together and form solid rock in a
process called compaction (pg. 104)



Classified as detrital, chemical, and organic
Water moving through soil picks up minerals and deposits
them between the sediments
Minerals such as quartz, calcite, hematite, and limonite act
as natural cement, making a detrital rock
Materials in Sedimentary Rocks
Detrital rocks have granular textures much like granulated sugar
They are named according to the shapes and sizes of the sediments that form
from them
Materials in Sedimentary Rocks
Conglomerate and breccia both form from large sediments-if sediments are rounded it is a conglomerate,
- if sharp angles, breccia (pg. 105)
sediments become rounded as wind/water moves them
Gravel-sized sediments in breccia/conglomerate can consist of any type of
rock or mineral, but often made of quartz, feldspar


Materials in Sedimentary Rocks
Concrete is made of gravel and sand grains that have been cemented
together, but it is not a rock because it doesn't occur naturally
Sandstone is formed from smaller, sand-sized sediments
Usually sandstone contains grains of quartz and feldspar


Materials Found in Sedimentary Rocks
Siltstone is similar except it's made of smaller, silt-sized particles
Shale is a detrital rock made mainly of clay-sized particles







Chemical Sedimentary Rocks
Chemical sedimentary rocks form when dissolved minerals come out of
solution
Minerals collect when seas or lakes evaporate
The deposits form sediments and rocks
Chemical sedimentary rocks are not made from pieces of preexisting rocks
Chemical Sedimentary Rocks
Limestone- calcium carbonate is carried in the ocean water and when it
comes out of solution as calcite, limestone forms








Clay sized particles are small enough to be compacted
together by pressure form overlying layers
Limestone usually is deposited on the bottom of lakes or
shallow seas
Large areas of the US have limestone bedrock
Chemical Sedimentary Rocks
Rock salt- when water rich in salt evaporates, it deposits the mineral halite
Halite forms rock salt
Rock salt deposits can range in thickness from a few meters to more than
400m. (pg. 107)
Companies mine these deposits because rock salt is an important resourceit's used in the manufacturing of glass, paper, soap, and dairy products, and is
table salt
Organic Sedimentary Rocks
Organic sedimentary rocks are made of the remains of once-living
things
One of the most common organic sedimentary rocks is fossil-rich






limestone
Like chemical limestone, fossil-rich limestone is made of the mineral
calcite (CaCO3) however fossil-rich limestone contains mostly the
remains of once-living creatures
Organic Sedimentary Rocks
Mussels, clams, corals, snails make their shells from CaCO3 that
eventually becomes calcite- when they die their shells accumulate on the
ocean floor
When these shells are cemented together, fossil-rich limestone forms
Coquina- rock made completely of visible shell fragments
Chalk & Coal
Chalk is another organic sedimentary rock that is made of microscopic
shells -while writing with chalk, you're crushing and smearing calcite shell
remains
Coal – another useful organic sedimentary rock




Coal forms when pieces of dead plants are buried under
other sediments in swamps
The plant materials are chemically changed by
microorganisms
The resulting sediment is compacted over millions of years
to form coal, important energy source
Carboniferous Period- 360 to 286 million years ago-when
most of the coal was produced (pg. 108)