Inside: How to use boric acid powder to grow crystal geodes inside duck or chicken eggs. Plus rock science printables: geode word search and crossword.
A geode is a hollow rock with sparkling crystals on the inside. How do the crystals get inside the rock? They grow naturally over millions of years. We don’t have a million years, but we do have some boric acid powder, which is all you need to grow gorgeous geodes that are almost as good as the real thing.
If your kids are like mine, the first question they are going to ask is how the rock got hollow in the first place. It turns out there are multiple ways this could happen.
In the case of volcanic rock, bubbles of carbon dioxide and water vapor might get trapped in flows of lava, and later dissolve, leaving empty space behind. In the case of sedimentary rock such as limestone or sandstone, minerals dissolve, and organic matter decays over time resulting in cavities.
Here are a few more points my kids brought up that you might find useful too.
How are geodes formed?
Groundwater and rainwater flows through rock cavities, leaving a variety of minerals – such as quartz, amethyst, and calcite – behind. These minerals create layers of different types of crystals and, over time, fill the empty space. The minerals grow towards the center of the geode. Which minerals end up inside the geodes vary by location and lots of other considerations such as acidity and temperature.
What color are geodes?
The shape and size of crystals inside the geodes are as unique as fingerprints, and no two geodes are completely alike, even if they are next to each other and are exposed to the same conditions. Most geodes have clear or white crystals. Sometimes colorization occurs as a result of impurities. For example, iron oxides impart rust hues. However, the extremely bright and unusually colored geodes you see on the internet are usually colored in the lab with artificial dyes.
Sparkly, glittery, bright, and beautiful geodes are surprisingly easy to make at home. Just follow along!
What you need
- Eggs shells (duck eggs are easier to cut into two halves than chicken eggs, which often crumble into many little pieces)
- Boric Acid Powder
- Jars, cups, or bowls for each eggshell half you will be coloring in this experiment (we used six)
- Food coloring (optional)
Note: Borax and boric acid are two different formulations of the same compound. Borax is sodium borate, while boric acid is hydrogen borate. In this experiment, we used boric acid powder. Just note that if you want to use Borax Laundry Detergent Booster instead, you might get different results.
What to do
- Boil eggs. Cool boiled eggs and cut with a sharp knife in half. If you are using chicken eggs, it might not be easy to get two halves from each egg. But as we discovered last year, duck shells are much easier to handle, and the geodes are bigger. Once you cut the eggs in half, scrape off the soft egg inside, and eat it (or add to a salad).
- Prep the workspace. Place eggshells into each container with the inside facing up. Set out food colorings if you are using them. Note: if you skip using food coloring, your crystals will be clear. Make sure you get everything set up before boiling the water, because you’ll need to work fast and use it while it’s hot!
- Boil water. Bring 3 cups of water to boil.
- Add boric acid. Stir in boric acid powder and keep stirring until it dissolves. Be careful not to leave some undissolved powder at the bottom of the pot, or the powder will be drawn away from the eggshells, and crystals will be formed around the bottom of the bowl instead of around eggshells. This is what happened to us in the past (pic below).
(Note: I recommend saving a few spoons for the Green Fire Experiment. This way, one jar works for two exciting activities. Otherwise, you can use the whole jar).
- Main action. Pour hot saturated water over the shells, and optionally add food colorings. As the borax acid powder cools, it settles on the eggshells and forms crystals.
- Let the shells sit overnight. Don’t stir, shake, or move the containers.
- Extract. When your geodes are ready, carefully remove them with a spoon, and let them dry on top of a piece of junk mail (or paper towel) at least for 12 hours. Don’t touch them with your skin, or your hands will get colored by the food coloring. Alternatively, break the top crust and put your geodes away for a few days. Outside is best. In our experience, all the liquid evaporates, and you get dry and clean geodes without the mess.
- Study. Get out a magnifying glass and study your geodes up close.
You want to see the real geode and our geode side by side?
The Greek root, geo-, means “earth-like,” probably because geodes look like little planets. You probably already know that geologists are the scientists who study rocks, and geology is the science that deals with the earth’s physical structure and substance. But do you know who petrologists are?
Petrologists are rock scientists. Petrology is the branch of geology that studies rocks and THE conditions under which they form. If you want to learn more about famous petrologists, read the biography of Ljudmila Mantuani and Otto Hahn.
Geode Word Search
Geode Crossword Puzzle
Additional Boric Acid Powder Uses
Now that you bought some boric acid powder, let me share something very useful. To the seasoned homemaker, boric acid is full of opportunities. It’s an excellent way to get rid of annoying pests like ants and roaches (just mix equal parts boric acid and flour and place it where your cat can’t get to it: under a stove or another tight space your kids and pets can’t access).
Boric Acid reduces the itch from mosquito bites (1 tsp of boric acid to 4 oz of water). And it removes annoying stains from toilet bowls (leave half a cup to a cup of powder for at least 30 minutes).
But the best use of boric acid powder by far is for mind-blowing kids’ activities. One of our favorites – and it happens to be one of the most popular experiments on the blog (with over 16 K shares) – is Green Fire. In this experiment, we used boric acid powder to color ordinary fire green. Another excellent activity, of course, is growing the crystal geodes that we described in this post!