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Grow Rock Candy

Whether it's big or small, rough or smooth, almost every rock is made of minerals. Each mineral has a unique crystal pattern and compostion.

Think about the mineral salt. It is made of cube- shaped crystals. No matter where you find it — on your table or at the beach — its crystals will be shaped like cubes. Look at the drawings of the crystals that make up diamonds, muscovite, quartz, and topaz. How would you describe their crystal shape?

diamond mineral

DIAMOND

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cubic crystal structure

Cubic
Structure

muscovite mineral

MUSCOVITE

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monoclinic crystal structure

Monoclinic
Structure

quartz mineral

QUARTZ

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triagonal / hexagonal crystal structure

Triagonal
Hexagonal
Structure

topaz mineral

TOPAZ

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orthorhombic crystal structure

Orthorhombic
Structure

The same mineral can have different colors. This is caused by small amounts of different elements that got into the mineral when it was forming. While the color of a mineral may vary, its crystal shape is always the same. 

For example, diamonds can be clear, yellow, pink, and even blue, but its crystals will always have eight faces (sides).

Now it's your turn to grow crystals by making rock candy!

The Materials

the materials needed including a pan, sugar, water, food coloring, a pencil, a paperclip, and string
  • an adult to help you
  • 1 pencil
  • 1 paper clip
  • tall glass
  • 1 piece of non-colored string (about 2 inches longer than the height of your glass)
  • 1 cup of water
  • 3 cups of sugar
  • 1 saucepan
  • stovetop or burner
  • clock or timer
  • food coloring

What To Do

Part 1: Start Your Crystals

1

Pour 2 cups of sugar and 1 cup of water into a saucepan.

one child pouring sugar into a saucepan while the other child pours in water
2

Stir the mixture over medium heat until the sugar disappears.

A cloudy mixture of sugar and water in a saucepan
the fully dissolved sugar in water mixture looks clear in the saucepan
3

Add 1 more cup of sugar, a little at a time. Keep stirring until the sugar disappears.

4

Turn off the heat. Take the saucepan off the heat and let it cool for 25 minutes.

5

While you are waiting, clean the paper clip with soap and water. Tie one end of the string to the pencil. Tie the other end to the paper clip.

tying one end of the string to a pencil
tying the other end of the string to a paper clip
6

Have an adult pour the mixture into the glass. (It helps to use a funnel or do this over a sink.)

7

Place the pencil over the top, letting the paper clip fall into the mixture. Let it sit on a counter for 12 hours.

pencil places across the top of the glass with the string and paper clip hanging into the liquid in the glass
8

Remove the pencil and string and set it aside. What do you see? (Sugar isn't a mineral, but it forms crystal shapes just as minerals do.)

the string with formed crystals places aside to dry on a paper towel

Part 2: Grow Crystals of a Different Color

9

Reheat the sugar mixture in a pan. Keep stirring until the sugar disappears.

10

Take the saucepan off the heat and let it cool for 25 minutes.

11

Have an adult pour the mixture into a glass. This, time, add a few drops of food coloring. Stir it well so that the color mixes throughout the liquid.

putting a few drops of red food coloring into glass with sugar and water mixture
stirring the food coloring well
12

Place the pencil over the top of the glass, letting the paper clip fall into the mixture. Let is sit for 12 more hours.

pencil and string placed on top of the glass with red food coloring and sugar water mixture
13

Remove the pencil and set it aside. What happened to the crystals? How would you describe the crystals that formed? Are they different from the first crystals you made?

Part 3: They Can Keep Growing and Growing and...

14

If you want to make your rock crystals bigger, keep repeating the steps above.

15

Before you eat your rock candy, be sure to cut off the paper clip.

As you can see, rock candy is really just a bunch of sugar crystals. Enjoy your tasty treat!

2 children about to eat the rock candy they made
Image Credits:

Photos: Diamond: courtesy of AMNH, Rondi Davies calcite and topaz: USGS; jadeite: courtesy of AMNH; all other photos: courtesy of AMNH