1
Name: ________________________________________ Homeroom: ____________
Chapter 7 – Earth’s Rocks
Essential Question: How Are Minerals Identified?
Properties of Minerals
A mineral is a natural, solid substance with a definite chemical composition and
physical structure.
Minerals are identified by using many different properties.
Streak - color of the powder left behind when a mineral is rubbed on a piece of unglazed
tile. The streak is most often the same color as the mineral.
A mineral that glows under ultraviolet light is said to show florescence.
A mineral is always a solid, with its atoms arranged in a certain repeating pattern.
A result of this patter is the mineral’s crystal shape.
Minerals tend to break along a plane, also known as a cleave, along flat surfaces
parallel to the crystal faces.
Mineral Hardness and Uses
Hardness measures the mineral’s ability to resist being scratched. The Mohs
hardness scale ranks minerals from 1 to 10, 1 being the softest and 10 being the
hardest. A mineral with a higher number has the ability to scratch a mineral with a lower
number on the Mohs scale. Diamonds are the hardest mineral; therefore they are a ten
on the Mohs scale and no other mineral can scratch a diamond.
2
Every mineral has a specific hardness that can then be compared with a different
mineral. Therefore hardness is the most useful for identifying the majority of
minerals.
Minerals have many everyday uses. The part of your pencil that writes on paper
is graphite, which is a very soft mineral. Minerals are also important sources of metals;
such as copper for computer parts, iron which is used to make steel, and even rock salt
which we eat.
How Minerals Form
Minerals form only in nature, from materials that were never alive. Most minerals
are compounds of several elements, but can also form from a single element.
Minerals form in many places such as seawater, the Earth’s crust, deep within
Earth in the mantle, as water evaporates in limestone caves, in mineral-rich hot water
from Earth’s crust, and in geodes.
Essential Question: How is Rock Classified?
Rock is a natural solid made up of one or more minerals. Rock makes up
landforms everywhere on earth.
Igneous Rock
The rock that forms when melted rock hardens is called igneous rock. Igneous
rock is the result when melted rock within Earth is pushed up from the mantle to the
crust.
3
This melted rock within the Earth is called magma. Once it is pushed to the crust
the cooler temperatures of the crust cause the magma to harden into rock - igneous
rock.
Upon reaching Earth’s surface magma is called lava. Since the temperatures are
much cooler on the surface lava cools much more quickly than magma.
Igneous rock is either intrusive cooling deep inside Earth’s crust, or extrusive
cooling on Earth’s surface.
Sedimentary Rock
Sedimentary rock forms when layers of sediment- bits of rock carved by wind,
water, or ice – settle over time and bind together. Sedimentary rock is divided into 2
main groups, determined by how the rock is formed.
Clastic sedimentary rock forms from rock that is broken into smaller pieces.
Chemical sedimentary rock forms when chemicals in water come out of the water
and form solids.
Limestone is a very common chemical sedimentary rock that forms when animal
shells or skeletons pile up at the bottom of an ocean or lake and become cemented
together and therefore form rock.
Sedimentary rock is most likely to exist near Earth’s surface.
Metamorphic Rock
Metamorphic rock forms when igneous, sedimentary, or metamorphic rock is
changed by pressure, heat, or very hot water. The process of forming metamorphic
rock is known as metamorphism.
4
Igneous and metamorphic rock both form where a land plate meets and ocean
plate because of the heat and pressure caused by the collision of the plates.
Essential Question: What is the Rock Cycle?
The Rock Cycle
All the processes that change rock from one kind to another is the rock cycle.
Any rock can become a different kind of rock. The rock cycle is constantly changing
Earth’s surface and the rock that makes up the surface.
The Rock Cycle and Plate Boundaries
The surface of the earth is made up of plates, it is not a single slab of rock.
These plates are very large and extremely heavy, but float on the soft rock that is
beneath them. At the boundaries where land and ocean plates meet and sometimes
collide, all three types of rock can form.
Essential Question: How do Soils Form?
How Soil Forms
Weather, the process by which rocks are broken down into smaller and smaller
pieces, is the most important factor in the process of soil formation. There are two
types of weathering:
Physical weathering – caused by wind, water, plants, and ice.
Chemical weathering – occurs when chemicals break up rocks, often in water, by
dissolving parts of them. This can be compared to a cement that holds pieces together.
5
There are three layers of soil.
The very bottom layer of the soil is known as bedrock and is mostly solid rock.
Bedrock is solid rock underneath loose materials. The minerals in bedrock help
determine the type of soil that forms. Since much of the soil in the upper layers forms
from bedrock.
Subsoil is the next and middle layer of the soil. Subsoil is mostly made of small
bits of rock, that are broken up by the help of temperature changes and tree roots that
force their way up through the soil. The upper part of the subsoil is rich with clay. The
upper part also contains minerals that were dissolved and filtered down from the top of
the ground.
Topsoil, is the top layer of soil. (Imagine that ) Topsoil is much more crumbly
than other soil layers. Topsoil contains bit of rock, air, water, and humus. Humus is
the decayed plant and animal matter. This rick mixture of ingredients is good for
growing plants, which need the phosphorus and nitrogen in humus to grow well. The
layer of topsoil is usually only a few centimeters thick.
Not all soils are the same. They vary in color, in the minerals they contain, and in
texture. One helpful clue in determining the kinds of minerals and the amount of
humus, iron, and oxygen is the soil’s color.
Conserving Soil
After the Dust Bowl, farmers could no longer farm because there was no soil left.
It had been blown away in the wind storms. As a result farmers had to change their
farming techniques and think of ways to conserve soil.
6
In order to save soil farmers now use several methods. They plant in rows so
that plants with shallow roots are next to plants with deep roots. The deep roots can
hold down the soil. They also practice contour plowing, where they plow across slopes
to prevent water and soil from flowing downhill.
Another important method farmer’s use is the planting of windbreaks. These
windbreaks are lines of trees that stop the wind from blowing away the soil.
It is important to conserve soil because it can take many thousands of years for
soil to form naturally; therefore it can not be replaced easily.