Lesson Plan – GEOS898

Dudley Friskopp - Litchfield Public Schools

Summary: This is a lab based investigation into the composition and formation of different types of sedimentary rocks and how grain size affects sedimentation.

Grade Level: Junior and senior high

Learning Objectives:

§ Students will make “fake rocks” and observe the rates at which different sized clasts sediment out of suspension.

§ Students will correlate their fake rocks with samples of actual sedimentary rocks and describe how these rocks form in nature.

§ Students will understand the role of cementation in the formation of sedimentary rocks.

Teacher Notes: This lab uses readily available materials to teach the makeup of sedimentary rocks. Day 1 of the lab should be done either as a kick off activity or immediately after the students read text coverage of sedimentary rocks. The rocks made during day 1 will need to be allowed to set a few days to dry before day 2 can be done. During this time a classroom lecture/discussion of sedimentary rock types, features and methods of formation would be appropriate. Day 2 is followed by the lab homework and a possible field trip to whatever local resources are available (ie. road cuts, cemeteries, quarries, etc.)

Plaster of Paris is messy stuff, so be prepared. You will want to demonstrate the proper ratio of water to plaster so that the result has a pudding-like consistency and how to stir so the clasts do not end up on the bottom of the cup. Do not allow any plaster to be washed down the sink! A sedimentation tube can be made from an 8-12 inch length of 1 inch diameter or larger plastic or glass tubing and 2 rubber stoppers. As an alternative, a pint jar with lid will suffice.

As the students make their rocks on day 1 someone should prepare a single cup with sand to which water has been added and stirred. This is allowed to sit along with the students cups. It makes a good discussion item after day 2 to show what happens without a cementing agent.

On day 2 most of the rocks will be too well cemented to break open by hand. The teacher should break those rocks open using a large straight screwdriver (as a chisel) and a hammer. Once all the students have broken their rocks open and filled in the Rock Name row of the data table, it would be a good time to discuss the makeup of each rock they made and what natural rock it represents using all appropriate sedimentary vocabulary. A discussion of depositional environment would be helpful as well.

Materials: Several pounds each of medium grained dry sand, fine dry powdered clay & dry gravel

large box of plaster of Paris,

paper cups (8-12 oz) - waxed cups work best – 6 cups per group

stirring sticks – 1 per group

wax marking pencils or crayons

sedimentation tube – 1 per group or 1 for a group demonstration