Lesson Plan

Rock Identification

Grade Level:
Upper Elementary: Third Grade through Fifth Grade
Lesson Duration:
60 Minutes
State Standards:
Colorado:
 4th Grade
(4-ESS1-1)
ESS1:C
 5th Grade
(5-PS1-3)
(5-ESS2-1)

Essential Question

How can the fine details in a rock’s appearance and texture help us determine how the rock was formed?

Objective

Students will make observations on hand samples of the various rock types seen at Florissant Fossil Beds and will correlate the different rocks with their stratigraphic sequence and deposition.

Background

  • Main Rock Types
    • Igneous: forms from the cooling & solidification of magma or lava. Mineral crystals are often formed in Igneous rock. Geologists can determine how quickly the magma or lava cooled by the crystal size.
      • Intrusive forms beneath the earth’s surface
        • i.e., Pikes Peak Granite in the Pikes Peak Batholith
      • Extrusive forms at the earth’s surface
        • i.e., Wall Mountain Tuff – a welded (hot) tuff (volcanic ash) with visible mineral crystals (phenocrysts) that are distinct from surrounding material.
    • Sedimentary: sediments are lithified (layered) and consolidated or cemented together. Fine grain rocks and minerals can be deposited in many ways or have many origins. As long as the layers are not altered by heat or pressure, the layers are still sedimentary.
      • Shale – alternating layers of ashy volcanic clay and other minerals
  • i.e., Florissant’s paper shale containing carbon impression fossils, fossilized single celled algae, and silica
        • i.e., lahars (Debris flows) like Mudstone and Caprock conglomerate
    • Metamorphic: heat and pressure alter existing rock deposits in shape, crystal formation, and texture. A sedimentary rock formation can become metamorphic if the Earth’s plates squeeze or bend the layers.
The Rock Cycle States that one type of rock can be transformed into another type if the right conditions are met. Materials that are ejected from a volcano are igneous in origin but can become sedimentary if they are then layered onto the bottom of a lakebed. Those sedimentary rocks can be described as volcaniclastic as they are volcanic in origin but reworked by sedimentary processes. The descriptions of larger rock layers, that happen over large portions of Earth’s history, can be mapped and illustrated to show the layers deep below our feet. This type of map is called a stratigraphic column. A strat column not only shows what we cannot see hidden below the surface, but also illustrates an important concept in geology: the principle of superposition. The principle of superposition states that the youngest rocks are superimposed (layered) on top of older rocks; therefore the youngest rocks are closest to the surface.

Preparation

Materials needed:

  • Compartment container with small rock samples from each Florissant type: Caprock conglomerate, Petrified wood, Volcanic mudstone, Paper shale, Wall Mountain tuff, Pikes Peak granite
  • Print outs of stratigraphic column (unlabeled & labeled)
  • Observation’s handout
  • Magnifying/hand lens
  • Pencil 
  • Print-out of rock cycle (labeled & unlabeled)

Preparation:

  • Check activity bin for all necessary supplies, including supplies needed from General Supply Kit.
  • Make copies of assessment questions, enough for each student to have one.

Materials

Download Rock Cycle (Blank)

Download Labeled Florissant Fossil Beds Stratigraphic Column

Lesson Hook/Preview

Rocks and minerals can tell a story of how Earth’s history unfolded in the ancient past. Rocks and minerals also contain distinct clues as to how they were form and in what order they were formed. By studying the rocks of Florissant, and how they are deposited in relation to each other, we can better understand Florissant’s distant history.

Procedure

  1. If there are enough supplies, students can work individually. Otherwise, separate students into small groups of 2-3.
  2. Give a brief lesson on the rock cycle. Help students fill in the rock cycle hand out for assessment question #1.
  3. Distribute rock sample boxes to each group, copies of the strat column, and enough magnifiers and assessment forms for each student to have one.
  4. Give a brief lesson on the purpose of this materials exploration, (page 1).
  5. Discuss with the students which rock on the strat column is the oldest, based on the principle of superposition. Write observations in question #2.
  6. Have students find the sample of Pikes Peak granite in their sample box. Have students discuss and write a brief description of Pikes Peak Granite, focusing on color, texture, and crystal sizes. Write descriptions in question #3.
  7. Have students find the sample of wall mountain tuff in their sample box. Give a brief lesson (or story) of how the volcanic “hurricane” occurred to create that rock. Have students compare the crystals in the tuff to the crystals in the granite and write their observations in question #4.
  8. Ask students to find the petrified wood in their sample box. Show them samples of larger pieces and the sliced pieces. Describe how the fossils were formed. Ask students to find a feature on their piece of petrified wood that reminds them of modern wood for question #5.
  9. Have students take out the last three samples (from their box. Have them discuss and describe texture and appearance. Write their observations and answer question #6.

Assessment Materials

Rock ID Assessment

  1. Have students fill out the hand-out on the rock cycle.
  2. Based on the principle of superposition, which rock on the Florissant stratigraphic column is the oldest? How do you know?
  3. How would you describe the Pikes Peak granite to someone who has never seen it? Describe its color, texture, and crystal size by comparing it to other things. For example: My sample of Pikes Peak granite is the color of a sunset and has crystals the size of ants!
  4. After comparing the crystals in the granite to the crystals in the Wall Mountain Tuff, how would you describe the difference? What makes the crystal size so different between the two types of rock?
  5. Is there any part of your sample of petrified wood that still looks like wood?
  6. Write at least one observation about each of the three remaining pieces of rock in your sample box. What about the three pieces is similar to each other? Is there anything about the three pieces that is different?

Rubric/Answer Key

  1. Rock cycle: see completed hand-out
  2. The Pikes Peak Granite is the bottom-most rock on the strat column. It is 1.08 billion years old.
  3. Descriptions will vary based on each student and what their sample of PP granite looks like. Encourage creativity! Discuss the variation of crystals from piece to piece and how that is a clue that the ancient batholith cooled slowly. Descriptions should include the overall pink tone with flecks of sparkly crystals in several colors.
  4. Students should be able to see the crystals in the tuff are much smaller and appear as phenocrysts.
  5. Petrified wood from Florissant still has the wood grain and growth rings. Students should still see or feel the texture of the rock resembles tree features, including splinters!
  6. Student answers will vary. Students should note that the caprock has a heavier feel, with pebbles fused into the rock—but has small bubble shapes. The shale and mudstone have an ashy feel. The shale contains fossil and strata layers while the mudstone has no layers. The mudstone may have visible fossils depending on the students individual piece.

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Last updated: September 10, 2022