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Growing Crystals
By John Cowens

The following simple activities will have you and your students growing edible and non-edible crystals in only a few days

growing sugar crystals

When growing sugar crystals, tiny crystals begin forming just after five days.

Recently, I attended our county fair and noticed children wearing multicolored candy necklaces. To eat the candy, they would simply stretch the elastic necklace to their mouths, chomp the candy and then rotate the necklace to a different position for the next bite.

A closer look
I chose to examine my candy necklace before eating it. Each piece of crystallized candy was similar to the formation of the rock crystals my students made in science class last year. Did you know this is one of the oldest forms of candy?

Macro molecular crystallographers know that minerals' atoms are arranged in a definite pattern. If not confined, the repeating pattern of a mineral's atoms form a solid called a crystal. A crystal has flat sides that meet in sharp edges and corners. All minerals have a characteristic crystal structure. In some mineral specimens, this structure is obvious from the specimen's appearance. In other specimens, this structure is apparent only on the microscopic level. Rather than waiting millions of years to form minerals into rocks, the following lessons make gorgeous crystals in a few days!

Background information
Macro molecular crystallographers grow crystals to develop the next generation of miracle medicines that have fewer side effects. Crystallography can also be used for ordinary items such as Crisco® (the greasy stuff used for cooking and baking) and an enzyme that's used in laundry detergent to get grass stains out of clothes.

Crystals can also be found in items such as calculators, computers, electronics, watches, telephones and lasers. Finally, crystals can be found in jewelry such as diamonds, rubies, emeralds and other gems that are crystals.

Incredible technology has made it possible to create crystals that have the same structure, composition and appearance as natural minerals. Examples of synthetic gemstones are sapphires and rubies that are placed in fine mechanical watches. Even the microcircuits, or chips, used in aircraft, satellites and nuclear reactors are formed on a base of synthetic sapphires. Lasers, compasses, electric meters, quartz watches and cloth-making machines are made from synthetic rubies and sapphires, too! Next time you buy something and the cashier runs it over a scanner, notice the glass plate. It's coated with synthetic sapphire to prevent the glass from scratching.

Making edible sugar crystals
Materials:

  • four cups of sucrose (granulated table sugar)

  • two cups of tap water

  • medium-size pot, beaker or saucepan (for heating and mixing the water and sucrose solution)

  • spoon for mixing the solution

  • heat source (stove or hot plate)

  • large clear jar (or anything that can tolerate boiling water)

  • either thick string, twine, a shoe string or bamboo skewer

  • food coloring (optional)

  • paper towel

Procedure:

  1. Place the granulated sugar into the medium-size pot for mixing and heating.

  2. Pour two cups of water into the pot and heat to the boiling point (212° Fahrenheit/100° Celsius) Add food coloring during this step if you want colored crystals!

  3. Stir the sugar into the hot water until dissolved or looks like syrup. Then, turn the heat off and allow the solution to cool for 15 minutes.

  4. Place a stick or bamboo skewer across the top of a large open jar. Tie two or three thick strings onto the stick. (The strings should be long enough to almost touch the bottom of the jar. Make sure the strings are spaced apart about 1 inch (2.5cm).

  5. Slowly pour the warm solution into the jar.

  6. Cover the jar with a paper towel and place the jar where it can be examined undisturbed.

  7. Within 24 hours, tiny crystals will begin to grow onto the strings. Larger crystals will form in 2 -3 weeks.

Extensions

  1. Add more sugar to the water to rapidly produce numerous small crystals.

  2. Have an adult pour the hot sugar solution into small containers for each student.

  3. To make colored crystals, add a drop of food coloring to the solution before crystals appear.

  4. Make rock candy on a stick. Soak a toothpick, bamboo skewer, or pipe cleaner in water. Then, roll it in granulated sugar and allow to dry. Pour the hot sugar and water solution into a heat resistant container and allow it to cool until room temperature. Place the stick, skewer, or pipe cleaner in the sugar solution. (Suspend it so it's not touching the bottom of the container.) The granulated sugar on the wooden stick will act as a "seeding," causing larger crystals to appear on the stick. Once the crystals have stopped growing, remove it from the solution and allow to dry.

  5. Make a candy necklace (like the one I ate at the fair). Try this with an elastic string tied into a loop. Follow the same procedures for making rock candy on a stick – Step #4. Once the crystals have stopped growing, remove the elastic string from the container and allow the crystal to dry before wearing it around your neck.

Non-edible table salt crystals
It's very simple to make salt crystals either from epsom salt or common table salt (sodium chloride).

Materials

  • two cups water

  • four cups of common table salt

  • heating source (stove or hot plate)

  • large glass jar that can tolerate heat

  • food coloring

  • string

  • stick or bamboo skewer - six inches long

  • three paperclips

Procedure

  1. Boil two cups of water.

  2. Slowly add four cups of table salt and food coloring. Stir the solution until the salt will no longer dissolve and starts to collect at the bottom of the pan.

  3. Allow the solution to cool for 15 minutes.

  4. Tie three strings onto the stick. On the opposite end of each string, attach a small paperclip. The strings and paperclips should be long enough to almost touch the bottom of the jar – make sure the strings are spaced apart about one inch. The paper clip will "seed" crystal formations.

  5. Slowly and carefully pour the warm solution into the jar.

  6. Cover the jar with a paper towel to keep the dust out.

  7. Place the jar where it can be examined but undisturbed.

  8. Within 24 hours, you'll begin to see tiny cube-shaped crystal formations growing onto the strings.

Additional resources

I hope that you and your students enjoy these activities – have fun!

John Cowens has taught for 26 years. He currently teaches sixth grade at Fleming Middle School in Grants Pass, OR.

November/December 2004, Vol.35, No.3