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Grade Level: 7-8
Purpose: To predict the appearance of a geode’s
internal structure based on its physical characteristics, such as mass
and density.
Suggested Goals: Students will collect accurate data
about the physical characteristics of a geode and determine a method for
predicting the internal structure.
Objectives: As a result of this lesson, students will
be able to:
- Use scientific equipment to collect data related to mass, volume,
and density.
- Form a hypothesis about a geode’s interior structures based
on collected data.
- Identify the common minerals found in Illinois geodes.
Time Required: 1-2 class periods
Group Size: Individually or by working in teams of 2-3
students
Background: Geodes are spherical bodies that may be
filled with layers of minerals and/or lined with crystals, such as quartz,
calcite, pyrite, and dolomite. Geodes form as mineral-rich water is trapped
inside an outer core of solid rock, including a layer of chalcedony. As
the temperature and pressure changes, the mineral matter inside the geode
precipitates to form a crystal lining.
Some geodes are filled completely, while others are hollow with a beautiful
display of crystals. Does the geode provide clues as to its internal structure?
For this experiment, challenge your students to document the physical
characteristics of a geode and make a prediction as to the internal appearance
of a geode.
Materials/Preparation:
- Set of geodes for display (already cracked open to show crystal structures)
- 8-10 unbroken geodes* (Labeled using 1,2,3, etc.)
- Triple-beam balances or electronic scales
- Overflow cans and graduated cylinders (or other method to measure
volume)
- Measuring tapes
- Safety goggles
- Hammer & Chisel
- Optional: Classroom display with minerals that are often found inside
geodes, such as quartz, dolomite, calcite, etc.
* If possible, obtain geodes from Illinois for this lab. Geodes may also
be ordered from science supply companies or rock and mineral dealers.
Skills: Students will need to be able to measure mass
and volume to calculate density. They will also need to be aware of proper
safety rules for breaking open the geodes.
Procedure:
- Share the sample geodes and discuss the formation of a geode as
outlined in the background section. If available, share the pictures
of the geodes in the ISM Geology Online collection. Refer to the ISGS
Geobit #3 listed in the reference section for more information about
Illinois geodes.
- Pass out the unbroken geodes and ask, “How can we tell what
the inside of a geode will look like?” or “Which geodes
will be the prettiest?” Create a list of possible physical characteristics
(mass, volume, density, texture, etc.) that might be used to predict
the internal structure. Students may also want to test the “sound”
of the geode, but must use care not to break it open during testing.
- Allow time for the students to collect data about their geode. They
should record as much information as possible on their Project Geode
Data Card. The students also need to make a prediction about the internal
structure or appearance of their geode. The predictions should be
specific, such as completely filled with large crystals or partially
filled with small crystals.
- OPTIONAL: If you have time available, allow the groups to record
data on more than one geode. Have the groups trade geodes, but not
the data cards. Groups should complete a new data card for each geode
as well as make a prediction.
- Before breaking open the geodes, have each group share their collected
data and predictions. Discuss similarities and differences between
the methods the groups used for their predictions.
- Demonstrate the proper techniques for breaking open a geode. Students
must wear safety goggles and be sure to keep fingers away from the
head of the hammer. You might want to choose 2-3 responsible students
to be the Smash Team and set aside a safe area for them to work.
- Once the geodes are broken open, have the students write a detailed
description of the internal structures on the bottom of the data card(s).
If a classroom display of common geode minerals is available, have
the students include the types of crystals found in the geodes in
the description. Students can also browse the ISM Geology Online GeoGallery
for specimens.
- Use the geodes and data cards to make a classroom display. Provide
time for the groups to discuss their predictions and compare the results.
Questions for discussion:
- What types of minerals did you find inside the geodes?
- How would you describe the internal structure or appearance of your
geode?
- Were your predictions correct? Why or why not?
- What is the most reliable method for predicting the internal structure
of a geode?
- Which geodes are the prettiest? What criteria should be considered—crystal
type, amount of crystals, or crystal size?
Extensions:
- Use Excel to create a spreadsheet of physical characteristics and
descriptions of internal structures. Students can manipulate the data
to investigate relationships between the individual characteristics
and internal structures.
- Use the Internet to research geode collecting sites in the state
or around the world. Provide a map and have the students use pushpins
and tags to label the best areas. Challenge students to create a list
of Geode Records detailing the largest geode, location with the most
geodes, most expensive geode, etc.
- Allow the students to create a brochure or children’s book
about geodes. The finished project should describe the process of
geode formation, the types of minerals found in geodes, and the location
of geodes in the state.
- Grow your own crystals in the classroom! For a variety of crystal
recipes, growing tips, and safety rules, visit http://rockhoundingar.com/pebblepups/growcryst.html.
Have the students keep a journal of their activities and record data
related to growth time, crystal size, colors, shapes, etc. The students
can use the collected data to make graphs or charts.
Assessment: Assessment of this lesson should be based
on the student’s ability to complete the data card by making accurate
measurements using the available equipment and the quality of the prediction
statement. Responses during classroom discussions should also be evaluated
to determine if students have met the lesson objectives.
Print Resources:
Web Resources:
State Science Standards:
- 11.A.3a: Formulate hypotheses that can be tested
by collecting data.
- 11.A.3c: Collect and record data accurately using
consistent measuring and recording techniques and media.
- 11.A.3f: Interpret and represent results of analysis
to produce findings.
- 11.A.3g: Report and display the process and results
of a scientific investigation.
- 12.E.3a: Analyze and explain large-scale dynamic
forces, events and processes that affect the Earth’s land, water
and atmospheric systems.
- 12.E.3b: Describe interactions between solid earth,
oceans, atmosphere and organisms that have resulted in ongoing changes
of Earth.
- 13.A.3a: Identify and reduce potential hazards in
science activities.
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