Fun and easy science experiments for kids and adults.

Crystal egg geode

Grow crystals on an egg shell in this experiment about geology. You get a nice ornament as a bonus.

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Video

Materials

2 dl aluminum potassium sulfate ("alum")
1 egg
Wood glue
1 paintbrush (or your finger)
Food coloring in any color
Measuring cups
1 pair of nail scissors (regular scissors also work)
1 bowl
1 spoon
1 pitcher that can hold at least 7 dl (3 cups)
1 needle (or thin nail)
Microwave (or other way to boil water)
Toilet paper
Water

Warning!

There is hot water in this demonstration.

There is also aluminum potassium sulfate ("alum") in this demonstration, which is an irritant.

Inhalation: Breath fresh air and rest.
Skin contact: Rinse with water.
Eye contact: Rinse with plenty of water. Get medical attention if necessary.
Ingestion: Drink plenty of water. Do not vomit. Get medical attention.

Environment!

It is okey to pour a mixture of alum and water into the sink, but dilute it with plenty of water.

Step 1

Source: "Incredible Egg Geode". Steve Spangler Science.

Wash the egg thoroughly.

Step 2

Use the needle to make a hole in one of the pointy ends of the egg. Poke around a little so that the hole becomes a few millimeters (1/8 inch) in diameter. Stir a little with the needle inside the egg to break the yolk.

Step 3

Do the same on the opposite side of the egg.

Step 4

Lean over the bowl and blow into one hole. The contents of the egg now shoot out through the second hole. Save for an omelette.

Step 5

Carefully cut the eggshell into two halves. Start in one of the holes.

Step 6

Take one half of the shell and remove any loose pieces. Wipe the egg with paper. Pour wood glue into the shell half and spread it out using the brush. Cover the entire inside of the shell, the edges, and a little bit on the outside, right at the edges.

Step 7

Powder generously with alum over the shell, so that all surfaces with glue are covered. Turn the shell upside down so that excess alum ends up on the table. Save this alum for later. Let the shell dry for 12 hours.

Step 8

Pour 475 ml (2 cups) of water into the pitcher and heat it in the microwave until it almost boils. Add 40-50 drops of food coloring och stir.

Step 9

Add 175 ml (3/4 cups) of alum. Use what you have saved on the table. Stir until all the alum dissolves. If all the alum doesn't dissolve, heat the mixture a little more. Then allow the mixture to cool for 30 minutes before continuing.

Step 10

Place the shell half in the pitcher. Use the spoon to gently push it down to the bottom. There it should lie with its inside facing up.

Step 11

Wait until the egg has as many crystals as you want. This can be as long as 15 hours, or as fast as 3 hours. Pick up the egg geode and let it dry on some paper.

Step 12

You can reuse the alum solution. Reheat it and stir. Remove all crystals that still don't dissolve. Then add a few teaspoons of alum to replace what had crystallized and stir until this dissolves. Add a new color if you want.

Short explanation

In this demonstration, a geode has formed - a hollow rock with crystals inside - in the same way as in nature.

Long explanation

Earth's crust, the outermost solid layer of our planet, is made up of thousands of different minerals. Minerals are chemical substances that (normally) form crystals and are formed on or beneath Earth's surface. Three common minerals are quartz, feldspar and mica. Minerals constitute the various rocks that exist. A rock is defined according to which mineral or minerals are included, its chemical composition and how it was formed. One common rock is granite, which consists of small grains of quartz, feldspar and mica. In granite, the different mineral grains can be easily distinguished with the naked eye, but this isn't always the case.

A crystal is a solid chemical substance whose atoms and/or ions form a structure that repeats itself in all three dimensions. All minerals thus form crystals, and have this ordered structure. Sometimes the crystals are microscopically small, but they can also be several meters in size.

A geod is a hollow part of Earth's crust, where minerals are deposited in special structures in the cavity. For example, it could be an air bubble that is trapped in lava that then solidifies. Afterwards, groundwater has seeped through the cavity and released small amounts of minerals at a time. These minerals have stuck in the cavity of the geode where they formed special structures. These special structures are often large crystals.

At the same time as minerals are deposited in the cavity of the geode, the outer walls of the geode solidify. This means that when a geod is then found, when erosion and weathering have exposed it, it looks like a normal rock among the rest of the rocks. By splitting the stone in half, you can find its beautiful interior.

In this demonstration, you have created your own geod. When you mix the mineral aluminum potassium sulphate ("alum") in water, it dissolves, which means that a mixture is formed where the components cannot be distinguished. By heating the water, more alum can dissolve, because both the alum and the water then move faster and thus mix more easily. When the water then cools, the solubility becomes lower again and the alum "falls out" of the solution and merges into crystals. The evaporation of water also contributes, as the amount of water that can dissolve alum then decreases. The alum crystals are formed primarily in places that are uneven, because the alum particles at those places find it easier to escape from the grip of the water molecules (water molecules hold together quite strongly). This is why you created some starter crystals on the eggshell in advance. This deposition of minerals is exactly what happens inside a natural geod.

Experiment

You can turn this demonstration into an experiment. This will make it a better science project. To do that, try answering one of the following questions. The answer to the question will be your hypothesis. Then test the hypothesis by doing the experiment.