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Lesson 2: Rock Stories

Overview

Wish you could take more field trips? You can! Your own schoolyard is filled with great geologic features! In this lesson, students learn that a rock's properties tell stories about where it came from and where it has been. The lesson illustrates how to make geologic observations and gives background about the important properties of rocks to observe. Students then use those observation skills to describe rocks they find on their own Schoolyard. This web site describes specific "geologic" features found on playgrounds (with photos and rocks from example schools).

Learning Outcomes
  • Not all rocks look the same, and the things that make rocks look a little different from one another give clues about each rock's "story".
  • Sedimentary rocks are made up of pieces of smaller rocks. For this exercise, we'll call them "grains", but they are often called "clasts".
  • Sedimentary rocks go through the following stages on the way to becoming a rock: Weathering, Erosion, Transport, Deposition, and Cementation.
  • Mechanical weathering is the process of breaking rocks into smaller pieces and then smoothing those pieces out.
  • Rusting metal is an example of chemical weathering.
  • GRAIN SIZE tells us about how much energy it took to move the grains. Transport of big grains (boulder sized) requires a lot of energy and can only happen in rapidly flowing rivers during floods, or massive landslides. Smaller grains can be transported in gently flowing streams, across lakes, and far out into the ocean.
  • GRAIN SHAPE tells us about the mechanical weathering history. In the process of being transported, mechanical weathering continues as rocks get smoothed and rounded over time. The longer a rock spends in a weathering environment, the rounder it gets.
Materials

Photocopies of a schoolyard or area surrounding your school where you have permission to take your class during school hours.

Download a presentation with prepared graphics and commentary as a Powerpoint or PDF file. Computer projector or overhead projector with color printer required (optional).

Since students might need to sit on the ground during some outdoor exercises, it can be good to warn them a day ahead to wear clothes that can get dirty. This can heighten the anticipation, as well.

Time Requirements

2-3 class periods.

Preparation: A few minutes of walking around your schoolyard looking for good examples of geologic building materials or natural rock outcrops and filling in a "mystery rock" description.

Downloads

Download the instructions as a single PDF File or a PowerPoint file with all the images.


Background Class Period 0
  • Your students should begin with an understanding of sedimentary rocks and their role in the rock cycle. We recommend that you review Sedimentary Rocks, which can also be printed and assigned as student reading.
  • We also recommend several activities from the Illinois State Museum. For introducing the rock cycle, we recommend: Ride the Rock Cycle, a kinesthetic learning game (appropriate for a wide range of ages).
  • Shortly after students have been introduced to different types of rocks, you can begin the activity below.
Introducing the Activity (Note: You can download a prepared presentation with this activity here)

Begin by asking students, "Close your eyes and picture 'a rock'. Did you picture a boring, grey stone?"

Pass around a few sample rocks to your class. Or, alternatively, show these photographs on an overhead. Tell students that these are examples of a few rocks. Either in pairs or by raising their hands, ask the students to describe features of the rocks. Write some of their responses on the board.

Tell students, "Not all rocks look the same, and the things that make rocks look a little different from one another give clues about each rock's 'story'. By making careful observations of a rock, geologists can tell where a rock came from and what has happened to it. Since every rock has a slightly different story, it's important to notice the differences in the rocks."

Image of rounded rock grains Image of rounded rock cobbles Image of angular grains in asphalt
Click on an image to enlarge it.

Using their own observations on the board, you can transition into a general discussion of important rock properties (see Class Period 1).


Instructions Class Period 1
  • In the opening activity, your students introduced some of the important properties to distinguish rocks. Begin this activity by reminding students about that idea, and add, "Since some rocks, called sedimentary rocks, are made up of pieces of bigger rocks that are combined, we can learn a lot about a rock by looking at the individual pieces that make it up."
  • Show a picture of a sedimentary rock. The tiny pieces that make up this rock are called 'grains.' These grains are one of the biggest clues about a rock's history, so we'll spend today learning to describe the grains. It is is important to note that when grains are cemented together into one big piece, we call that whole piece a rock. So when you walk outside onto your playground, geologists would refer to the entire surface as a single rock made up of smaller pieces called grains. Also see Misconceptions section below.
  • Go to Rock Stories: Describing Sedimentary Rocks. Use the photographs and description on the following web page to introduce the definition of grains, COLOR, GRAIN SIZE, and GRAIN SHAPE.
  • Pass out photocopies of the Rock Description Table and Student Instructions. Students will need several pages of the blank tables.
  • Using an image of a rock on the overhead projector, fill in the table as a class. For example, start with this photo of a schoolyard conglomerate. As you introduce each property, refer to the instruction page about the type of information they are expected to fill in.
  • Discuss with students the interpretation of these properties. Use the information in Describing Rocks and Example Descriptions to determine the history of this particular rock sample. Show an image of the environment (e.g., gentle stream, landslide, etc...)
  • Show an image of another rock. Ask students to silently fill out a second copy of the table for this rock. They can raise their hands with individual questions.
  • Now ask the students if they can interpret their observations. What was this rock's story?
Class Period 2: Geologic Excursion to the Schoolyard
  • Start the class by reviewing the rock properties from the previous lesson.
  • The class is now ready to apply their knowledge "in the field." They will need a pen, a few blank copies of the Rock Description Table and Student Instructions, a ruler, and something firm to write on in the field (a book or binder). Begin by taking the class outside.
  • Walk around the schoolyard and have students point out where they see rocks. Walk them past any geologic building materials (brick, concrete, asphalt, sandbox, etc...) or natural rock outcrops (if you are lucky enough to have one at your school site) that you know.
  • Have each student or pair of students pick a small area of the "rock" that they will describe. It's often best to have students sit down on the ground while doing their description ("Real geologists aren't afraid to get dirty."). Have students fill in the blank table with a description of their rocks. After a few minutes, have students move to another location.
  • Hand out photocopies of a "mystery rock description" (a Rock Description Table that you filled out for a certain exposure of rock). Have the students go hunting for this particular rock exposure.
Homework Give students a few blank copies of the Rock Description Table and have them fill it out for geologic materials at home or on their way home. Be sure to instruct them that they are NOT allowed to describe any roads (for safety).

Have students draw a picture of the history of one rock that they described. If they think that their rock came from a raging river, have them draw a picture of it.

Common Misconceptions

Misconception: When completing the activity, many students go up to a rock whose grains are actually smaller pieces of rock and only recognize that the individual grains are rocks. They don't acknowledge that the whole thing is itself a rock made up of smaller rocks.

Fact: In geology, we call a rock made up of other pieces of rock a sedimentary rock. If those pieces are made up of individual grains of sand, we call the bigger rock a sandstone. If those pieces are bigger, like pebbles or boulders, we call a huge rock with all the pieces together a "conglomerate." Many schoolyard rocks are conglomerates. Teachers should be sure to point out that the whole of a playground might be a single conglomerate rock because it is made up of pieces of smaller rocks cemented together into one piece. Ask students, "how big are the individual grains of the rock you found? How big is the whole rock, with all the grains put together?"

 

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