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The Classic Lake Superior Agate Is Made up of Red and White Bands of Quartz

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The Classic Lake Superior Agate Is Made up of Red and White Bands of Quartz LAKE SUPERIOR AGATES – HOW DID THEY FORM? The classic Lake Superior Agate is made up of red and white bands of quartz. They formed in vesicles (gas bubble holes) of the lava that flowed out onto the surface of the earth about 1 billion years ago. Have you found an agate? What did it look like? Do you collect them? Where do you think it came from? And how did it form? Author Rick Meyer – Pine River – Backus Schools, Pine River, MN http://webdom.org [email protected] Aug. 2006 Contributers John D. Marshall Scott Wolter Objectives Upon completion of this unit, you should be able to: ● describe several different types of Lake Superior Agates. ● identify on a map where Lake Superior Agates formed. ● identify on a map where Lake Superior Agates are found today and explain how they got there. ● explain two different theories on the formation of Lake Superior agates. ● identify different structures found in the agates. ● use the evidence (structures) to support one of the theories. Resources Lake Superior Agate, Scott Wolter, 1999, Outernet Publishing, ISBN: 1581752067 - An excellent reference book available at bookstores or online. http://www.lakesuperioragate.com The Other Lake Superior Agate, John Marshall, 2003, Llao Rock Publications, Beaverton, Oregon, ISBN: 0972256822 - An excellent reference book. There is a pdf version that can be ordered from the author by contacting him at: [email protected] The Beauty of Banded Agates, Michael Carlson, 2002, Fortification Press, Edina, MN, ISBN: 0972189106 – An exploration of agates from 8 major sites. http://www.agatenodule.com/ This unit has been designed for grades 7-8 but can be adapted for other Audience levels. This unit focuses on Earth Systems Understandings 1 and 3. {Key words: 1= Earth Systems beauty & value, 2=stewardship, 3=scientific process, 4=interactions, 5=change through Understandings time, 6=Earth as a subsystem, 7=careers & hobbies} http://www.ag.ohio-state.edu/~earthsys/ Contents Part 1 – Introducing Agates - Where did they form and Where are they found? Part 2 - Identifying Lake Superior Agates and their structures Part 3 - Formation Theories Part 4 – Design and Conduct Experiments Part 5 - Scientific Debate – Can you support your theory? Teacher Notes This activity might be used as part of a rock and mineral unit. It could also be used to conclude a unit on the scientific method and experimenting. The experiments in Part 4 are open ended and student designed. The main thing that the teacher should be looking for is experimental design and safety. Is there a variable? Is there something that can be measured or documented for results? Is the experiment safe and going to be conducted under safe conditions? The interpretation of the results must be looked at as clues to the puzzle of agate formation – not as answers or proof. Extensions You might have students research other types of agates. Some other agate types / names are: Brazilian, Condor, Dryhead, Fairburn, Mexican, lace agate, moss agate, ..... You could have students find and print pictures of agates from the web. You could ask students to bring in agates they have found. Use a tumbler and tumble a load of agates. Tumblers can be loud. Find a location where it will not disturb others. Do not tumble large agates without letting students know that that many collectors prefer the natural beauty. Part 1 Introducing Agates Materials Agates, pictures of agates, copies Agate Formation – An Introduction that students can complete. Procedure Use questions to see how many of your students have agates, collect agates, have tumbled agates. Agate collecting can be a great hobby. Show the students agates. You can use pictures (printed or projected). You might ask students to bring in some examples that they have found. Ask students what they know of how they formed and where they come from. Print out copies of agate articles for the students to read some basic information. Example articles are: Lake Superior Agates, Minnesota DNR, 2006, http://www.dnr.state.mn.us/snapshots/rocks_minerals/lakesuperioragate.html The Lake Superior Agate: Digging into MN Minerals, Minnesota DNR, 2006, http://www.dnr.state.mn.us/education/geology/digging/agate.html Have students complete the map and answer the questions while you discuss the following events that lead to the formation and distribution of Lake Superior Agates. Outline: 1. Mid-continental Rift – 1.2 -1.1 billion years ago. 2. Lava flows out on the surface during rifting. Hundreds of flows pile up over time to a thickness of up to 22,000 feet in some places. 3. The weight of these lava flows cause a depression to form along where the rifting took place. (Think of having liquid flow up and pile up on a mattress. It will sink where the heavy weight get piled on.) Lake Superior sits in part of this depression but it did not exist at the time of the rifting. Lake Superior has only existed as it is now since the last glacial ice age (a few thousand years.) 4. As each lava flow spreads out on the surface and cools, gas bubbles in the liquid lava get trapped as the lava cools. These gas bubbles are called vesicles. The largest number of vesicles are normally at the top of the lava flow. (Think of a can of soda that you open. The bubbles rise to the top.) 5. Hot water (heated by the magma still below the surface) dissolves silica from the rock and carries it through fractures in the rock into vesicles. The silica (SiO2) or quartz along with other minerals get deposited in the vesicles. 6. The basalts / lava flows started weathering from the time that the rifting stopped (1.1 billion years ago) until glaciation which began about 2 million years ago. During this long time period, the basalt was weathered chemically and physically to form soil. The agates, mainly quartz, were left behind because they are resistant to weathering. 7. Glacial lobes advance and melt away from about 2 million years ago until about 10,000 years ago. As the glaciers advance they pick up soil and rock and transport it moving it south. They also scrape and gouge out the softer rock. Glaciers deposit the rock and soil as till, moraine and outwash deposits. 8. Glaciers that advanced through the rift area are responsible for transporting agates as far south as Nebraska. If you look in glacial material that came from what was the rift area, it is possible to find Lake Superior agates. 9. The best places to look are where that type of rock is concentrated. Gravel pits (with permission), landscape rock (gravel) rocky beaches, fields (with rocky soil) and gravel roads are just a few of the places to start looking. Agate Formation – An Introduction. Name: _________________________ Label the following features and answer the questions. 1. Label the location of the Mid Continental Rift. 2. Draw arrows showing the direction the land surface was moving during the rift. 3. When did rifting take place? ______________________ For how long? _________________ 4. What happened during the rifting? ________________________________________________ _______________________________________________________________________________ 5. What happened to the land / rock surface after the rifting stopped? _______________________ _______________________________________________________________________________ 6. When did glaciation take place? ___________________Draw a line showing the maximum extent of glaciation. When did the last glaciers melt out of Minnesota? _______________ 7. Draw a line outlining the location where Lake Superior agates can be found. 8. What does this information tell you about Lake Superior agates: ____________________________ __________________________________________________________________________________ __________________________________________________________________________________ Part 2 Identifying Lake Superior Agates and Their Structures Materials Pictures of agates and their structures, agates Procedure Hand out the pictures or project the pictures or provide actual agates that illustrate different features. The pictures on the next pages include examples with the following features / types of agate. Discuss each and have students write their definitions on the provided handout. If you print out the pictures, have students write down the type of agate or feature being illustrated. Each picture may have more that one label. Have students draw arrows if there is more than one feature illustrated. 1. Fortification Agates – banding that on a complete agate forms a complete layer. 2. Water Level Agates – flat or parallel banding. 3. Moss Agates – crystal structures of other minerals encased in the chalcedony. 4. Tube Agate – banding forms around a needle like crystal suspended in the silica gel. 5. Sagenite Agate – suspended needle like crystals of another material such as rutile in the agate. 6. Ruin Agates / Healed Fractures – agates that have been deformed or broken while in the lava and then new solutions heal or seal the fractures. 7. Eye Agates - hemispherical banding on the surface of the agate. 8. Geode – an agate or cavity lined with crystals and a hollow / open center. 9. Crypto or micro-crystalline (microscopic) and macro-crystalline (visible) structures. 10. Flow structures – indications of movement of the silica gel while forming. Agate Types and Features Name: _________________________ Write your own definition of each of the agate types or features as discussed in class. 1. Fortification Agates – 2. Water Level Agates – 3. Moss Agates – 4. Tube Agate – 5. Sagenite Agate – 6. Ruin Agates / Healed Fractures - 7. Eye Agates - 8. Geode – 9. Crypto or micro-crystalline and macro-crystalline structures - 10. Flow structures – Look at each of the pictures on the following pages. Try to identify the agate type or feature being illustrated. If more that one type or feature is illustrated, label and use arrows to point out each feature. Some of the labels will be used multiple times. Agate Types and Features Illustrated Name: _________________________________ 1. 2. _________________________________ ____________________________________ _________________________________ ____________________________________ Comments/Questions: Comments/Questions: 3.
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