Download sedimentary rocks

Elements,
Minerals and
Rocks
With this chapter we turn our attention to the
Lithosphere.
It is the earth’s surface which provides the ingredients
from which life is formed and is the stage upon which the
drama of life is played out.
Over 70% of the Lithosphere is covered by the
hydrosphere.
The rocks that the Lithosphere contains tell the story of
its multi-billion year past.
The Lithosphere’s surface is ever changing. It is pushed
and pulled by forces found in the interior of the earth
and on the exterior.
This presentation will deal with the makeup of the
Lithosphere - the Elements, Minerals and Rocks!
The study of the solid earth is called: GEOLOGY.
A ROCK can be defined as a combination of a variety of
minerals in a solid state.
A MINERAL is a naturally occurring, inorganic
substance possessing a definite chemical composition
and atomic structure.
Think of a chocolate chip cookie as a rock. The cookie
is made of flour, butter, sugar & chocolate. The cookie
is like a rock and the flour, butter, sugar & chocolate
are like minerals. You need minerals to make rocks, but
you don't need rocks to make minerals. All rocks are
made of minerals.
Minerals are made up of a variety of elements.
An ELEMENT is a material that cannot be subdivided by
ordinary methods into simpler materials. Elements are
classified in the Periodic Table that you should be
familiar with in Science. There are 91 natural occurring
elements found in rock. These 91 elements can combine
to form at least 2000 different minerals.
The most common Minerals are: Plagioclase, Quartz,
Orthoclase and Mica to name a few.
The most common Elements are: Oxygen, Silicon,
Aluminum, Iron and Calcium to name a few.
A vast number of minerals exist, together with a great
number of their combinations into rocks. Some rocks are
very simple to analyze, for example Diamonds are pure
carbon (carbon is an element). Some composition of rocks
are complicated, such as Granite. The next slide
illustrates the makeup of Granite:
Most rock is extremely old, but rock is also being
formed at this very hour as a volcano emits lava that
solidifies on contact with the atmosphere.
Rock can be classified into three categories depending
on how they were formed:
IGNEOUS
SEDIMENTARY
METAMORPHIC
The majority of this presentation will deal with how
each one was formed and giving some examples along the
way.
The final set of slides will illustrate THE ROCK CYCLE,
which is a diagram that links the formation of the above
types of rocks.
IGNEOUS
• Igneous rocks are called fire rocks (or ‘born of fire’)
and are formed either underground (Intrusive) or
above ground (Extrusive).
• Underground, they are formed when the melted
rock, called magma, deep within the earth becomes
trapped in small pockets. As these pockets of magma
cool slowly underground, the magma becomes igneous
rocks.
• Igneous rocks are also formed when volcanoes erupt,
causing the magma to rise above the earth's surface.
When magma appears above the earth, it is called
lava. Igneous rocks are formed as the lava cools above
ground.
Some examples of Igneous Rocks:
Granite rocks are igneous rocks which were
formed by slowly cooling pockets of magma that
were trapped beneath the earth's surface.
Granite is used for long lasting monuments and
for trim and decoration on buildings.
Pumice rocks are igneous rocks which were
formed when lava cooled quickly above
ground. You can see where little pockets of air
had been. This rock is so light, that many
pumice rocks will actually float in water.
Pumice is actually a kind of glass and not a
mixture of minerals. Because this rock is so
light, it is used quite often as a decorative
landscape stone. Ground to a powder, it is used
as an abrasive in polish compounds and in
Lava soap.
Most Metallic Minerals such as Gold, Silver, Zinc, nickel,
lead and copper are Intrusive igneous Rock.
We find a lot of these minerals in the Canadian Shield.
SEDIMENTARY ROCKS
• For thousands, even millions of years, little pieces
(sediments) of our earth have been eroded--broken
down and worn away by wind and water etc.
• These little bits of our earth are washed downstream
where they settle to the bottom of the rivers, lakes,
and oceans. Layer (called Strata) after layer of eroded
earth is deposited on top of each. These layers are
pressed (Pressure is a key word) down more and more
through time, until the bottom layers slowly turn or
solidify into rock.
• This strata can be folded, warped or cracked to form
mountains like the Rockies. Remember the forces that
do the folding are called Tectonic forces!
• fossils are often found in sedimentary rocks, giving us
clues to past life since we can accurately date the age of
the rock in which the fossil was laid down.
• Coal, oil and natural gas (fossil fuels) are found in
sedimentary rock where large quantities of marine plants
and animals in ancient seas were buried and partly
decomposed as the sediments turned into rock.
• Sediments made from broken rock are known as
CLASTIC MATERIAL
• Sediments made from chemical or organic material are
known as N0N-CLASTIC or BIOGENIC.
• Many Non-Metallic minerals such as Salt, Potash,
Phosphate and Gypsum are sedimentary rocks
Pressure from overlying layers (strata)
Some Examples of Sedimentary Rocks:
Sandstone rocks are sedimentary rocks made
from small grains of the minerals quartz and
feldspar. They often form in layers as seen in
this picture. They are often used as building
stones.
Limestone rocks are sedimentary
rocks that are made from the mineral
calcite which came from the beds of
evaporated seas and lakes and from
sea animal shells. This rock is used in
concrete and is an excellent building
stone.
Metamorphic Rock
• Metamorphic rocks are rocks that have "morphed"
into another kind of rock. These rocks were once
igneous or sedimentary rocks.
• How do sedimentary and igneous rocks change? The
rocks are under tons and tons of pressure, which
fosters heat build up, and this causes them to change.
If you exam metamorphic rock samples closely, you'll
discover how flattened some of the grains in the rock
are. These flattened grains create layers or strata.
•This banded structure called FOLIATION can help
use differentiate a Metamorphic rock from an
Igneous rock. (See the picture of Gneiss in following
slides)
Some examples of Metamorphic Rock:
Schist rocks are metamorphic. These
rocks can be formed from basalt, an
igneous rock; shale, a sedimentary rock;
or slate, a metamorphic rock. Through
tremendous heat and pressure, these
rocks were transformed into this new
kind of rock.
Gneiss rocks are metamorphic. These rocks
may have been granite, which is an igneous
rock, but heat and pressure changed it. You
can see how the mineral grains in the rock
were flattened through tremendous heat and
pressure and are arranged in alternating
patterns.
The percentage of the earth’s crust is made up of :
65% Igneous
8% Sedimentary
27%Metamorphic
The process of replacing older rocks with new ones is
called the Rock Cycle. The next slide illustrates this
cycle:
The Rock Cycle:
Source:http://geog.ouc.bc.ca/physgeog/contents/10a.html
The Importance of Rocks and Minerals
Rocks and Minerals provide many of the raw
materials used to manufacture a wide range of
consumer items. The following are some examples
or scenarios describing how important Minerals
and Rocks are to our everyday life:
1: Southern Ontario is famous for the abundance of
building materials found nearby. Sand and Gravel
(aggregates) resulted from the last Ice Age. The Oak
Ridges Moraine just north of Toronto is one such
source. When the last great ice sheet started to melt
and recede, the load of tiny grains and even large
boulders that it was carrying were deposited. Much of
this material was carried away by meltwater running
through enormous spillways. Most of Southern Ontario
was a depository for this sand and gravel.
2: Another area in Southern Ontario where
building materials are found in the Niagara
Escarpment. The escarpment is the remains of an
ancient sea bed that was raised by tectonic forces
millions of years ago. The limestone found here is
very resistant to erosion and is used for all kinds
of construction.
Other minerals used in construction are clay,
gypsum, aluminum and graphite .
3. Some of the minerals (intrusive) we use are very rare
and therefore difficult to find. It is the work of
geologist to find prospective mineral concentrations so
they can be extracted from the earth’s crust. The basic
questions a geologist must answer is: Is the mineral in
sufficient quantity and concentration to mine profitably?
If it costs more to extract than a company would make
selling it, there there is no point in mining the mineral.
World prices and Market demand also play a role. If
these factors combine to make an ECONOMIC DEPOSIT
will a company make an investment to open a mine.
Many economic deposits exist in the Canadian Shield and
Western Cordillera part of Canada. These can be
classified into three categories:
Precious Metals: gold, silver, and platinum.
Ferrous Metals (containing iron to make steel alloys):
iron and nickel.
Non-Ferrous Metals: copper, lead, and zinc, tin,
aluminum and salt.
The above minerals have made Canadian Mining
Companies Internationally known.
4. Oil and Natural Gas are two other valuable resources
found in the earth. While these resources are fluid as
opposed to solids like gold and iron, their extraction
from the earth is also considered mining. Below is a brief
outline of how Oil and Gas are created:
•Occurred millions of years ago
•Dead plants and animals called Plankton accumulated in
shallow seas.
•Plankton stores large quantities of carbon as CO2.
•This CO2 was converted into carbohydrates by
photosynthesis.
•This fossilized sunshine was trapped in the sedimentary
rocks that formed above it.
•This layer of organic ooze decomposed very slowly
because there was a lack of oxygen.
•Bacteria transformed it into methane and a complex
hydrocarbon called kerogen. If the temperature rose
above 1000C, the kerogen changed into oil.
•A concentration of oil occurs when the oil
accumulates in spaces of porous (can be permeated by
fluid or air) rock which are sandwiched by non-porous
rock. See the diagram on the next slide.
•The Athabasca Oil Sands found in Northern Alberta
are interesting because the oil is not found in a neat
reservoir but the oil is mixed with sand and shale.
Extraction of the Oil Sands is difficult and costly.
The Athabasca Oil Sands:
Source: Earth Matters, by Ron Chasmer, Oxford University Press.
5. Coal is another valuable fossil fuel found in
sedimentary layers. The following is a brief
description of the formation a Coal:
•Formed from living things
•Giant forests grew in shallow tropical swamps
•When the trees fell they decomposed slowly
•Methane and peat (flammable organic substance) are
formed
•If the layers of peat were buried under sediments
and heated, water vapour was squeezed out and coal is
created
•Coal, unlike oil is easily mined and does not need to be
held in place by non-porous layers.
Formation of some popular minerals including coal:
Source: Planet Earth, by Gary Birchall, John Wiley and Sons.
THE END!