Grow crystals at home: salt and sugar geodes

Materials and supersaturated solution

You need a clean glass jar, 2 cups of very hot water, 6 tablespoons of salt or sugar, a cotton string, a pencil and a spoon. Tie the string to the pencil, lay it across the jar mouth and let the string hang without touching sides.

Stir salt or sugar into hot water until no more dissolves and a little powder stays at the bottom. This supersaturated solution holds extra material, pour it into the jar, cover loosely with paper and leave it still for crystal growth.

Atoms stacking and giant caves

Crystals grow because dissolved atoms lock into neat repeating rows like tiny bricks stacking perfectly. As water slowly evaporates over 3 to 7 days, more atoms join the surface and sharp cubes or spikes become visible daily.

Real caves show the same process on a huge scale over thousands of years. In the Naica cave in Mexico gypsum crystals reach 11 meters long and weigh 55 tons because warm mineral water stayed still for a very long time.

• Use hot but not boiling water
• Do not move the jar for 7 days
• Salt makes cubes sugar makes spikes
• Filter solution for clearer crystals
• Naica cave holds 11 meter crystals