Curious Crystals

Can you identify an unknown crystal by comparing its appearance to other known crystals?

In this activity, students will carefully look at four known household crystals. After observing and describing the crystals, students will be given an unknown crystal, which is chemically the same as one of the four known crystals but looks different. The other activities in this investigation are examples of tests students can conduct on the crystals. After a series of these tests, students will gather enough evidence to identify the unknown crystal.

Materials needed for each group

• • Salt

  • Epsom salt

  • MSG (Accent®)

  • Sugar in cup

  • (unknown)

  • 5 Small cups

  • Black construction paper, ½ piece

  • Magnifier

  • Masking Tape

  • Pen

  • Plastic Spoon

Notes about the materials

Be sure you and the students wear properly fitting goggles.

Procedure

• 1. Use masking tape and a pen to label four corners of a piece of black construction paper: sugar, salt, Epsom salt, and MSG. Label the center unknown.

  2. Place small samples of Epsom salt, table salt, sugar, and MSG on the labeled areas of the construction paper.

  3. Use a magnifier to look carefully at each type of crystal. Describe the physical characteristics of each crystal and write responses in all sections of part 1 of Physical Properties of Solids Assignment Sheet.

  4. Get the “unknown crystal” and follow the previous step. Note: this unknown is chemically the same as one of the other crystals you just looked at.

  5. Compare the unknown to the four known crystals by circling the boxes of the four known crystals that are similar to the unknown. Then add up totals for each column and answer the questions at the end of part 1 (base your answer and explanation on the evidence).

Have students discuss their observations.

From http://www.inquiryinaction.org/