Subterranean Alum Crystal Eggshell Geode Geochemistry

35 mins Ages 6-11 Indoor

An engaging, screen-free learning activity that builds real-world creativity and critical thinking for kids aged 6 to 11.

Materials Needed

  • • Clean eggshell halves (membranes peeled) (2 halves)
  • • Potassium alum powder (spice aisle) (3/4 cup)
  • • Liquid food coloring (blue, purple) (1 bottle)
  • • PVA craft glue and paintbrush (1 set)
  • • Wide-mouth heatproof glass jar (1 unit)

Pro Tips

  • → Paint the inside of a dry eggshell half with craft glue and dust with alum powder to create nucleation seed sites.
  • → Dissolve alum powder in hot water with food coloring until no more dissolves (supersaturated solution).
  • → Submerge the seeded eggshell in the cooling solution: sparkling crystalline geode clusters sprout across the shell interior over 15 hours.

Safety First

Adult handles hot water; alum is safe but not for consumption.

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Step-by-Step Instructions

1

Step 1

Coat the inside of clean dry eggshell halves with glue and sprinkle alum powder to form seed crystals.

2

Step 2

Dissolve 3/4 cup alum powder into 2 cups of near-boiling water, stirring until completely dissolved.

3

Step 3

Stir in 10 drops of food coloring, let cool slightly, and gently submerge the seeded eggshell halves.

4

Step 4

Rest undisturbed for 15 hours, then lift out and dry your glittering mineral eggshell geode.

What they are learning

Solute supersaturation crystallization Nucleation seed growth mechanics Natural mineral geode formation