Geodes are geological formations, appearing as ordinary rocks on the outside but revealing a cavity lined with shimmering crystals inside. The term “geode” originates from the Greek word “geoides,” meaning “earthlike,” referring to their typically rounded or egg-like shape. While natural geodes take millions of years to form, creating similar crystal-filled formations at home offers an accessible way to explore the science of crystal growth.
Understanding Geodes
Natural geodes begin their formation in hollow spaces within rocks, such as gas bubbles trapped in cooling volcanic lava or cavities left by dissolved tree roots or animal burrows in sedimentary rock. Mineral-rich groundwater then seeps into these voids, depositing layers of dissolved minerals on the inner surfaces. Over vast periods, these minerals slowly crystallize and grow inward, forming the characteristic sparkling linings of geodes. The home crystal growing experiment mimics this natural principle by using a supersaturated solution, where dissolved minerals precipitate out of a liquid and form crystals as conditions change. It also utilizes a “seed” surface, like the inner wall of a shell, to provide a starting point for crystal growth, similar to initial mineral deposits in a natural geode.
Gathering Your Materials
To grow your own geode-like crystals, you will need a few common household items. Borax, a laundry booster and cleaning product, serves as the primary crystal-forming substance. Hot water acts as the solvent, dissolving the borax to create the solution from which crystals will grow. For the “geode” mold, you can use eggshell halves, plastic containers, or pipe cleaners shaped into desired forms.
Additional tools include:
A pot for heating water
A spoon for stirring
String or twine for suspending your mold
A skewer or pencil to hang the mold in the solution
When handling borax, exercise caution: ensure adult supervision, avoid ingestion, and consider wearing gloves to protect your skin.
The Crystal Growing Process
Begin by heating water to a rolling boil in a pot on the stove. Once hot, gradually add borax powder, about three to four tablespoons for every cup of water. Stir continuously until no more borax dissolves, and you see a small amount of undissolved powder at the bottom. Heating the water allows it to dissolve more borax than it normally could at room temperature, creating this supersaturated state. If the solution appears cloudy, your finished crystals might also be cloudy.
Next, prepare your chosen “geode” mold, whether an eggshell half or a pipe cleaner shaped into a coil or snowflake. If using pipe cleaners, tie a string to your shape and attach the other end to a skewer or pencil. Carefully pour the hot supersaturated borax solution into a heat-safe container, such as a glass jar. Gently lower your prepared mold into the solution, ensuring it is fully submerged but not touching the sides or bottom.
Covering the container loosely helps to slow the cooling process, which promotes the growth of larger, more defined crystals. Crystals begin to form within a few hours, with significant growth visible after 12 to 24 hours as the solution cools and the borax precipitates.
Ensuring Success and Solving Problems
Achieving crystal growth requires attention to a few details. Ensuring the solution is fully saturated is key; continue adding borax until no more dissolves, even if a small amount remains at the bottom. Always start with boiling water to maximize borax dissolution and create a supersaturated solution. Allowing the solution to cool slowly and remain undisturbed is important for forming larger, well-structured crystals. Avoid jostling the container during the growth period.
If crystals are not forming, the solution may not have been sufficiently saturated, or it might have cooled too quickly. Conversely, if crystals appear small or cloudy, it could indicate that the solution was too concentrated or cooled too rapidly. For a colorful display, food coloring can be added to the borax solution before suspending your mold. Once your crystals have grown, carefully remove them and allow them to dry completely. Borax crystals can be susceptible to humidity over time, so to preserve their appearance, consider coating them with clear nail polish or storing them in a sealed container with a desiccant.