Saturday Science Sessions – Egg Geodes

Since Saturday, egg shells have been sitting in my fridge. Growing crystals. Using science to create egg geodes!

Geodes are crystals that form in the cavities of sedimentary rocks and in the gas bubbles of igneous rocks. These porous rocks have enough empty volume that water is able to seep through the spaces, carrying dissolved minerals.

These minerals are deposited in the holes in the rocks, slowly over time growing as more minerals are deposited. Examples of the crystals include quartz, calcite, and celestite.

Simulating geodes requires a few basic ingredients:

• Washed, cleaned, and dried egg shells
• A container to hold the shells
• Epsom salts
• HOT water
• Measuring cup
• Food coloring

For six egg shells, mix approximately 1/4 cup of the Epsom salts into 1/4 cup of hot water (almost boiling). The water should be nearly saturated with the salts – essentially to the point where adding more salts will not dissolve in the water.

Pour the water and salts into each of the egg shells and add food coloring to give the crystals color. Place the container of egg shells into a refrigerator and let it sit for at least 3 hours. The crystals will start to form in long needle shapes!

(A variation of this experiment uses Alum powder, which produces shorter and less finger-like crystals.)

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