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Title: Can You Judge a Geode by its Cover?

based on 4 ratings
Author: Nancy Rogers Bosse

Grade Level: 6th - 8th; Type: Earth Science

Objective:

To investigate whether rocks containing geodes can be determined from the outside.

Research Questions:

  • How are geodes formed?
  • Do geodes form in any rock?
  • Can you tell if a rock is a geode by the outside?

Geodes are formed in empty spaces inside rocks. Fluids containing minerals make their way into a rock’s cavity and crystals begin to grow. From the outside they look like an ordinary rock, although they are usually round or oval and have a hard, bumpy texture. Geodes can form inside volcanic or sedimentary rock. They can be found in many places throughout the world.

Materials:

  • geodes (at least 5)
  • hammer
  • googles
  • old sock
  • towel
  • paper
  • pencil
  • ruler
  • camera (optional)

Experimental Procedure:

  1. Gather the necessary materials.
  2. Rinse the geodes and allow them to dry.
  3. Take pictures or sketch the unopened geodes. If you are using opened geodes, turn them face down so that only the outside is exposed. Write a description of the outside of each geode including information about its size, shape, and color. Make a prediction about what you think you will find inside the geode.
  4. With the help of an adult, open the geodes one at a time. Follow the directions for opening that come with your geode.
  5. Take a picture or sketch the inside of each geode. Write a description of each geode including information about its size, shape, and color. Compare the actual descriptions with your predictions.
  6. Analyze the data and draw a conclusion. Does the outside of a geode predict what is on the inside?

Terms/Concepts: geode: a cavity in a rock lined with crystals quartz: a common mineral found in rocks mineral: a solid substance found inside the earth; rocks are made up of minerals; Geodes are beautiful crystal cavities inside ordinary rocks. Geodes form in empty spaces of rocks. They form when the right combination of fluids and minerals seep inside the empty space of a rock.

References:

“How to Break Open a Geode” at http://www.geodegallery.com/breakinggeodes.html “How are Geodes Formed?” at http://earthsky.org/earth/how-are-geodes-formed geodegallery.com rocksforkids.com

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