Crystals are found in many different shapes. In fact, scientists can look at the shape of some crystals and easily know what substance they are observing. They can also discover many things about substances by studying crystal shapes, which they often do with the help of a microscope. Although crystals are large compared to many other things that scientists look at using a microscope, a variety of things can be learned by observing crystals in different ways. In this activity you will be observing some of the special properties of crystals by observing them with your eyes, a compound light microscope, and polarizers.

Required Materials

• Crystals
• Cellophane tape and Magic brand transparent tape
• Slides
• Field microscope
• Polarizers
• White paper and pen
• Science notebook

Activity Directions

1. Follow your teacher's directions for making the crystals. In your science notebook, write down the procedure you used in making the three types of crystals. Include any questions that you have and answer the following questions:

   What substances did you use to make crystals?

   How do you make a supersaturated solution?

   What was the solvent in each of the solutions?

2. Look at the crystals of other students at your table.

   Are they all the same shape and size?

   If not, why do you think there are differences?

3. Think about the variables that seem to help promote crystal growth.

   If you made these same crystals again, what would you do to ensure that your crystals were the largest they could be?

4. In your science notebook, draw and label each crystal sample. Decide the crystal shape of each sample. For example, if you used table salt, draw what your crystals look like and label it cubic.

Mini-Activity Directions: Observing Birefringence

1. Take 2 different glass slides. On one place a strip of clear cellophane tape and on the other place a strip of magic brand transparent tape.

2. Place one of the polarizers above the slide, and one below.

3. Slowly rotate the polarizers and observe any changes. One of the two slides contains the tape that is birefringent, or double refractive. Which one is it?

4. Describe briefly in your science notebook what you noticed about the birefringent tape.

	Interactive Java Tutorial
Double Refraction Explore birefringence by looking through a piece of Iceland spar to see a double image.

Mini-Activity Directions: Calcite, A Natural Birefringent Material

1. Place a glass slide over some text and observe the writing. Now place a calcite crystal over some text and look at the light coming through the crystal.

   How does this differ from what you observed when looking through the plain glass slide?

2. Make a small dot on a piece of white paper, lay the calcite crystal over it, and view the dot through the crystal. Rotate the crystal while it is laying over the dot. Explain what you see by writing your observations in your science notebook.

3. View the images of the dot created by the calcite crystal through the polarizer.

   Is either image polarized?

4. Lay the polarizer over some print and then lay the calcite crystal over the polarizer so that you view the print through both the polarizer and the crystal.

5. Describe what happens when the crystal is rotated in the plane of the print.

6. Now, look at your crystal samples using polarizers and the compound light microscope. In your science notebook create a chart similar to the one below.

Crystal Name	Crystal Shape	Birefringent - Yes or No




7. Using the following prompt, write 3 paragraphs in your science notebook about crystals.

   Crystal patterns are repeated over and over again. Before you begin writing, think about what you have learned about crystals and about what you observed. Now explain to someone who has never seen crystal shapes how a crystal looks under a microscope.

8. Discuss with other students in your class the similarities and differences among the drawings. Also discuss your answers to the questions you wrote in your science notebook.

	Interactive Java Tutorial
Polarized Light Microscopy See what various crystallized samples look like through a polarized microscope. Samples include a moon rock, a dinosaur bone, spinach and others.

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