• 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.

Prepared graphics in a presentation, complete with commentary, are available for you to download as a Powerpoint or PDF file. Computer projector or overhead projector with color printer required. (optional)

Since students may 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.

• Your students should begin with an understanding of sedimentary rocks and their role in the rock cycle. We recommend that you review the following web page about sedimentary rocks, which could also be printed and assigned as student reading:
  <Sedimentary Rocks>

  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 (usable for a wide range of ages).

  Shortly after students have been introduced to different types of rocks, you can begin the activity below.

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."

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).

• 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.

  Use the photographs and description on the following web page to introduce the definition of grains, COLOR, GRAIN SIZE, and GRAIN SHAPE.
  

  <Rock Stories: Describing Sedimentary Rocks>

• 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?

• 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.

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.

U.S. Department of the Interior | U.S. Geological Survey
URL: http://education.usgs.gov/schoolyard/
Page Contact Information:USGS Education Web Team
Page Last Modified: 24 July 2006