Download Unit 3 Lesson 3 Rock Cycle

Grade 9 Geography - Unit 3 Lesson 3
The Rock Cycle
What is the difference between a Rock and a Mineral?
Minerals are homogeneous, naturally occurring, inorganic solids. Each mineral
has a definite chemical composition and a characteristic crystalline structure. A
mineral may be a single element such as copper (Cu) or gold (Au), or it may be a
compound made up of a number of elements. About 2,500 different minerals
have been described.
Rocks are made up of one or more minerals.
There are three types of rocks.
Igneous Rocks - Formed from the cooling of molten rock.
Volcanic igneous rocks formed from molten rock that cooled quickly on
or near the earth's surface.
Plutonic igneous rocks are the result of the slow cooling of molten rock
far beneath the surface.
Sedimentary Rocks - Formed in layers as the result of moderate pressure on
accumulated sediments.
Metamorphic Rocks - Formed from older "parent" rock (either igneous or
sedimentary) under intense heat and/or pressure at considerable depths beneath
the earth's surface.
The interrelationship among the rock types is referred to as the Rock Cycle.
There are four main layers that make up the Earth.
Inner Core - A mass of iron with a temperature of about 7000 degrees F.
Although such temperatures would normally melt iron, immense pressure on
it keeps it in a solid form. The inner core is approximately 1,500 miles in
diameter.
Outer Core - A mass of molten iron about 1,425
miles deep that surrounds the solid
inner core. Electrical currents
generated from this area produce the
earth's magnetic field.
Mantle - A rock layer about 1,750
miles thick that reaches about half the
distance to the center of the earth. Parts of this
layer become hot enough to liquify and become
slow moving molten rock or magma.
Crust - A layer from 4-25 miles thick consisting of sand
and rock.
The core, mantle and crust of the earth can be envisioned as a giant rock recycling
machine. However, the elements that make up rocks are never created or destroyed
although they can be redistributed, transforming one rock type to another.
The Recycling Machine Liquid (molten) rock material solidifies either at or below the surface of the earth
to form igneous rocks. Uplifting occurs forming mountains made of rock. The
exposure of rocks to weathering and erosion at the earth's surface breaks them
down into smaller grains producing soil. The grains (soil) are transported by wind,
water and gravity and eventually deposited as sediments. This process is
referred to as erosion. The sediments are deposited in layers and become
compacted and cemented (lithified) forming sedimentary rocks. Variation in
temperature, pressure, and/or the chemistry of the rock can cause chemical
and/or physical changes in igneous and sedimentary rocks to form metamorphic
rocks. When exposed to higher temperatures, metamorphic rocks (or any other
rock type for that matter) may be partially melted resulting in the creation once
again of igneous rocks starting the cycle all over again.
Since most of the earth's surface is covered by water - molten material from inside the
earth often breaks through the floor of the ocean and flows from fissures where it is
cooled by the water resulting in the formation of igneous rocks. Some low grade
metamorphism often occurs during and after the formation of the rock due to the
intrusion of the material by the sea water. As the molten material flows from the fissure,
it begins forming ridges adjacent to it.
If we examine the rock cycle in terms of plate tectonics, as depicted in the figure above,
we see that igneous rocks form on the sea floor as spreading ridges. As the rocks cool,
and more magma is introduced from below, the plate is forced away from the spreading
ridge, and acquires a sediment cover. As shown in the figure, in this case, the oceanic
plate eventually "dives" under the adjacent continental plate. As the oceanic plate
travels deeper, high temperature conditions cause partial melting of the crustal slab.
When that occurs, the surrounding "country rock" (existing adjacent rock) is
metamorphosed at high temperature conditions by the contact. The molten material is
either driven to the surface as volcanic eruptions, or crystallizes to form plutonic igneous
rocks.
Recognizing Rocks
How Do I Know What Rock I Have?
Type
Igneous
Features
interlocking texture of the grains
the presence of vesicules (holes)
in extrusive igneous rocks
may be dark-colored and heavy
Example
Granite
may display two grain sizes, one
much larger than the other
Sedimentary
grains cemented together
the presence of fossils
light-colored and light weight
may display interlocking grains but
is very light weight
Metamorphic
interlocking texture of large grains
foliation (layering)
banded light and dark colours
"ching" sound instead of a "chunk"
sound when tapped
Sandstone
Shale
Coal
Marble
Slate
Figure 1. Rock Cycle
Grade 9 Geography - Unit 3
Geological History
Geological Time Scale in Terms of the 12-Hour Clock
When
Time
Topic
Era
(Millions of Years)
12-Hour Clock
Earth's Formation
Precambrian
4600
12:00
First Rocks
3800
2:05
Single-Celled
Organisms
3600
2:36
540
10:36
Fish
480
10:45
Land Plants
410
10:55
Insects
400
10:57
Amphibians
370
11:02
Reptiles
340
11:07
Conifers
320
11:10
230
11:23
Mammals
210
11:27
Birds
145
11:37
Flowering Plants
125
11:40
67
11:50
25
11:56
<2
11:59
Shellfish
Dinosaurs
Paleozoic
Mesozoic
Last Dinosaurs
Grass
Cenozoic
Humans
(0.26%)
(2.85%)
(7.51%)
(89.39%)
Grade 9 Geography of Canada - Unit 3
Rocks and Minerals
Mineral - a natural substance which has its own distinctive structure and may have
its composition expressed with a chemical formula. Some examples are quartz,
calcite, and galena. Quartz has the chemical composition Si02. About 100 minerals
are relatively common. There have been over 4000 minerals identified.
Rock - usually composed of two or more minerals in some physical combination,
although some rocks are composed of only one mineral. Examples of rocks are
limestone, sandstone, granite, or shale.
(If you wanted to think of a comparison to food, a mineral would be like flour and
sugar, and a rock would be a cake.)
Properties of minerals - You can tell the differences between minerals by looking for
certain properties. Because each mineral is unique both chemically and structurally,
each has its own set of physical, optical, and structural properties to aid in its
identification.
Chemistry refers to the basic building blocks that the mineral is made of. Optical
properties are the way a mineral looks and what light does when it shines on it. Physical
properties such as hardness and streak can be tested easily.
Physical properties
Physical properties may be divided into two groups:
(1) those concerned with the effects of light on the mineral, and
(2) other tests.
Light-dependent properties: The easiest tests to do are about how light interacts with
the mineral. These are color, luster and diaphany. You can do all of these light tests
using only your eye.
Color is the most obvious property of the mineral , but it is also the least used
because a given mineral, like quartz, may have a variety of colors (colorless, purple,
blue, pink, black, violet, green, tan, et cetera).
Luster is easy to tell by looking at the mineral. Does the mineral reflect light like a
piece of metal? If so, then it has metallic luster. If not, then it has non-metallic luster.
Non-metallic luster is further subdivided into how brilliant the mineral reflects the
light: vitreous (like glass), adamantine (brilliant, bright like metal), pearly, greasy,
oily, dull, etc.
Diaphany means how translucent the mineral is. Can you see through it like a clear
crystal, or not? Or maybe just a little. The answers for diaphany may be opaque,
translucent, or transparent. This property is usually noted for a thin chip of the
mineral because if the mineral is strongly colored, it may mask this property.
Other Properties of Minerals
Specific gravity - measure of each mineral's own unique density and how it compares
to the density of water. The mineral's density is what makes the mineral heavy or light.
Some minerals are very dense, like the native metals copper, silver, or gold, and some
are even lighter than water and will float! Volcanic pumice will float on water. You have
to have a specially designed balance to measure specific gravity.
Quartz is always a good mineral to compare another sample to, since it has a specific
gravity of 2.54. Minerals with a specific gravity higher than around 3.2 are considered to
have relatively high specific gravity. They either contain heavy atoms, like those of the
middle of the Chemist's Periodic Table (titanium, manganese, iron, cobalt, nickel,
copper, zinc, lead) or have a very dense packing arrangement of the atoms (like with
carbon in diamond).
Streak is an easy field test to do. Interestingly, the powder of a particular mineral may
or may not be the same color as the mineral! Using an unglazed piece of porcelain, like
the back of a common bathroom tile, you can do a streak test. The color of the
powdered mineral (the streak) may surprise you. Try it for a piece of pyrite (fool's gold).
Hardness measures how hard the mineral is relative to other minerals. It is called the
scratch or hardness test. Most minerals will not scratch a quartz crystal. Many years
ago, a man named Moh took a lot of minerals and tried to scratch them with each other.
From his experiment, he came up with chart of the relative hardness of his minerals,
one to another. This chart is called Moh's hardness scale. Talc is the softest, diamond is
the hardest.
A chemical test allows us to determine if the mineral reacts with dilute acid. We use a
drop of 10% hydrochloric acid to check for effervesence, or fizzing, and note if there is
a reaction.
Grade 9 Geography of Canada - Unit 3 Lesson 3
Ice as a Mineral – Can a Mineral be a Rock?
Is ice a rock or a mineral? Are all rocks made of minerals? Can a mineral be a rock?
Earth is made of solids, liquids, and gases. The atmosphere and oceans surrounding
the planet are the main gas and liquid parts, although there are liquids (magma) and
gas within the Earth, too. The solid part of the Earth, though, is basically rock. Now
rocks are made of minerals. A rock can be made of a single mineral. Or a rock can be
made of many minerals.
A mineral has to satisfy the following criteria:
be inorganic
naturally occurring
crystalline
solid
definite chemical formula
unique physical properties
Now, let's see if ice fits these criteria.
Inorganic? Ice is not "organic" in the sense that it is not animal or vegetable matter.
Naturally occurring? Snow, ice in glaciers, etc. are natural.
Crystalline? Ice has a crystalline structure (it can be hexagonal or cubic) with atoms of
hydrogen and oxygen covalently bound in water molecules and water molecules bound
together in the crystal structure by hydrogen bonds.
Definite chemical formula? Ice is always H20.
Definite physical properties
"Solid"? …How do you define a solid? …Does ice qualify? In the true, technical sense,
ice is a crystalline solid. And natural ice should be considered a mineral. Some people
also consider glacial ice as rock.
Activity - Is It a Mineral?
Indicate whether the substances listed in the left column are minerals
(yes or no) and why or why not. An example is provided.
Substance
Mineral
Why or Why Not?
window glass
no
no regular internal structure
ice
___
___________________________
water
___
___________________________
Teflon
___
___________________________
lead
___
___________________________
pencil lead
___
___________________________
gold
___
___________________________
plastic
___
___________________________
diamond
___
___________________________
chlorophyll
___
___________________________
steam
___
___________________________
coal
___
___________________________
carbon dioxide
___
___________________________
sulfur
___
___________________________
stainless steel
___
___________________________
table salt
___
___________________________
mercury
___
___________________________
tin
___
___________________________
Activity - Is It a Mineral?
Indicate whether the substances listed in the left column are minerals
(yes or no) and why or why not. An example is provided.
Substance
Mineral
Why or Why Not?
window glass
no
no regular internal structure
ice
Y
water
N
liquid mineral
Teflon
N
not naturally occurring
lead
Y
pencil lead
Y
gold
Y
plastic
N
diamond
Y
chlorophyll
N
organic
steam
N
gaseous mineral
coal
N
organic
carbon dioxide
N
gas
sulfur
Y
stainless steel
N
man-made
table salt
Y
halite
mercury
Y
tin
Y
graphite
not naturally occurring, organic