BIG IDEA:
Rocks and minerals have properties
that can be: observed, tested,
described, identified and recorded.
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What does the object look like?
Where have you seen it before?
What is it used for?
What do you think it is?
We recently learned that crystals are present in
minerals as one of 6 shapes. Geologists can use the
crystal shapes found in minerals as an identification
tool because the same pattern of crystals will be
present in that mineral no matter where it is found.
Today we are going to use the materials our geologist
has sent to start investigating one of the ways crystals
are formed.
How are crystals in minerals formed?
I think we can use the materials the geologist has sent
to make our own crystals if we…
because…
Naturally, crystals are formed in one of two ways and
these two processes are referred to as crystallization.
Crystallization
The process by which crystals are formed. When molten minerals
solidify or when minerals are deposited from evaporated solutions.
Unfortunately in a classroom setting we don’t have the
ability to watch minerals crystallize when melted rock
solidifies, but we can observe the formation of crystals
by evaporation.
Evaporation
The conversion of a substance from a liquid to a gaseous state.
I know you have all experienced or observed in some
form the evaporation of water.
When a liquid such as water evaporates it changes
from a liquid state to a gaseous state. The solid
particles in that liquid cannot be turned into a gas so
they are left behind.
Have you ever noticed how a puddle of water will often
be replaced with a ring or stain when the water has
dried up or evaporated? The stain left is made up of
the solid particles often called sediment... sand, dirt,
tiny rocks, minerals, etc. that were mixed in with the
liquid. The solid particles left behind could crystallize.
Many of us had a very difficult time identifying the shape
of the crystals found in our samples. Part of the problem
was because the crystals were too small to see with our
magnifiers.
If all crystals of a particular mineral have the same shape
than why are some crystals larger than others?
The size of the crystal is determined by how fast it is
formed. The faster a molten material cools, or a solution
evaporates, the smaller the crystals will be. The slower the
molten material cools, or a solution evaporates, the larger
the crystals will be.
Before we begin to form our crystals I would like you to
reflect back to the salt crystals I showed your groups.
What shape were these small crystals?
We are going to dissolve salt crystals into a solution and see
if we can recrystallize them through evaporation.
Prediction
What shape do you think the crystals you form will be
and explain your reasoning?
We will observe what happens to our solution and add details
to our science notebook. Each time we make an observation we
should include an accurate drawing and description.
Salt Crystal Solution Observations
Salt Crystals
Day ____
Day ____
Day ____
Before Mixing
Picture
Picture
Picture
Picture
Description
Description
Description
Description
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How are crystals in minerals formed?
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How can minerals be identified by the shape of their
crystals?
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Minerals contain crystals and there crystals can only be one
of 6 shapes.
Why were the crystals we created cubic?
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Molten minerals solidify
Evaporation - Minerals are deposited from liquid solutions
Salt is a mineral and it’s crystals are cubic. Salt will always
have cubic crystals no matter were it is found and how it is
formed.
Why are some crystals larger than others?
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The size of a crystal is determined by how fast it is formed.
Slow = Bigger Crystals, Fast = Smaller Crystals
Based on what you have learned from your investigation
of crystals, you need to record at least 3 claims and
evidence statements in your science notebook.
I claim that…
I know this because…
Possible Examples:
I claim that all minerals contain crystals I know this
because…
I claim that you can identify minerals by the shape of
their crystals. I know this because…
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What did you learn…?
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What really surprised you…?
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What new questions do you have…?
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What would you like to know more about…?