Download What are rocks?

A Unit study on
Rocks and Minerals
for
rd
3
grade
Essential
Question:
What are the
similarities and
differences between
rocks and minerals?
Enduring
Understandings
• Rocks are made of minerals.
• Rocks & minerals can be classified using
physical attributes such as color, shape,
texture, & hardness.
• The environment can change rocks over
time.
• You can perform a streak test to compare
hardness of rocks and minerals.
Table
of Contents
1. Rocks
2. Types of Rocks
3. Rock Cycle
4. Minerals
5. Differences
6. Weathering and Erosion
What are rocks?
• Rocks and stones are naturally occurring solids
made up of minerals.
• The Earth's crust is made up of rock.
• Rocks have been used by humans
for millions of years, from early
tools and weapons through to
various construction materials.
• There are three different types
of rocks based on the way they
form, igneous, sedimentary and
metamorphic.
Since a rock
can be
composed of
several
minerals, it is
classified
according to
the process
of its
formation.
Igneous Rocks
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.
Sedimentary Rocks
For thousands, even
millions of years, little
pieces of our earth have
been eroded--broken
down and worn away
by wind and water. These
little bits of our earth
are washed downstream
where they settle to the
bottom of the rivers,
lakes, and oceans. Layer
after layer of eroded
earth is deposited on top
of each. These layers are
pressed down more and
more through time, until
the bottom layers slowly
turn into rock.
Metamorphic Rocks
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.
Rock Cycle
The Rock Cycle
is a group of
changes. Igneous
rock can change
into sedimentary
rock or into
metamorphic
rock.
Sedimentary
rock can change
into
metamorphic
rock or into
igneous rock.
Metamorphic
rock can change
into igneous or
sedimentary
rock.
The changes that rocks go through is called
the rock cycle, and it goes something like this:
The earth pushes
rocks up to the
surface, where they
go through changes
caused by erosion, the
weather, and
compacting.
Erosion refers to the process of water breaking down
rock over time. The weather, including sunlight, also
causes rocks to break down. Compaction, on the other
hand, is when accumulated sediment is pressed together
to form sedimentary rock. Usually, this happens when
sediment flows into a river or other body of water. The
pressure of the water "squeezes" the sediment together,
compacting it.
Eventually, these forces press the rocks back down into
the earth, where they are heated by pressure within the
earth. The intense pressure and heat underground
presses the rocks together and, over time, can melt them
into magma. Some of that magma may reach the surface,
where it cools off and becomes solid, igneous rock again!
What are minerals?
• Minerals are naturally occurring substances formed by
geological processes.
• Physical properties of minerals include hardness (Mohs
scale), luster (how it reflects light) and color, as well as more
complicated properties such as streak, fracture, cleavage
and density.
• Mohs scale of hardness measures the ability of minerals
to scratch each other. Talc is very soft and is listed as 1,
diamond is very hard and is measured as 10.
• There are over 4,000 different types of minerals.
• Only around 30 of these are commonly
found in the Earth's crust.
•
Minerals have
certain properties,
or attributes, that
help to identify
them.
•
Minerals can be
identified by their
color, luster, streak,
hardness, and
clevage.
Color
• Color is not always a
good clue to the
identity of a mineral.
• Many minerals are
found in several
colors and many have
extra chemicals in
them that give them
an unexpected color.
• Also, weathering may
change the color of
the mineral.
Example- quartz comes
in various colors: rose,
milky, and clear.
Luster
Luster is the way a
mineral reflects light.
Chrysocolla-dull
Minerals can be described as
metallic, pearly, glassy, silky,
greasy, brilliant, or dull.
Talc-pearly
Diamond-brilliant
Pyrite-metallic
Opal-greasy
Quartz-glassy
Gypsum-silky
Streak
Streak is the color made by
rubbing a mineral across a
hard, rough surface like a
bathroom tile.
Example- pyrite is a
brassy, yellowish
color. However, it
makes a greenish,
black streak when
rubbed across a
streak plate.
Hardness
Hardness is measured by seeing how easy it is to scratch
a mineral. Each mineral is used to scratch the other
minerals to see the order from softest (talc) to hardest
(diamond).
A German mineralogist, Friedrich Mohs,
developed a standard scale of hardness in
1822.
Cleavage
Cleavage is when certain minerals break in a definite
way.
Muscovite breaks into
blocks.
Feldspar breaks into little
steps.
Halite breaks into cubes.
Calcite cleaves into slanting
bricks.
What are the differences between
rocks and minerals?
• It is not easy to tell the difference between rocks &
minerals because there are so many kinds of them.
• A mineral is one solid formation that occurs naturally in
the earth, while a rock is a solid combination of more
than one mineral formations which is also occurring
naturally.
• A mineral is defined by its structure and shape.
• Since a rock can be composed of several minerals, it is
classified according to the process of its formation.
What is weathering
and erosion?
•
Weathering is the process where rock is dissolved, worn
away or broken down into smaller and smaller pieces.
•
Once the rock has been weakened and broken up by
weathering it is ready for erosion.
•
Erosion happens when rocks and sediments are picked up
and moved to another place by ice, water, wind or
gravity.
•
When ice melts or wind and water slow down they can't
carry as much sediment. The sediment is dropped, or
deposited, in landforms.