We are just loving Steve Spangler Science, a website full of science projects you can do at home. One of the coolest is to make your own geodes out of eggs. A real geode (top photo) is a rock whose inside is full of crystals. Crystals form from materials that line up in smooth, flat, shiny faces. Table salt is crystal-shaped, as are the diamonds in jewelry. Crystals inside geodes might be made of the purple stone amethyst, the pink stone rose quartz, or some other stone or mineral. Here, you can make your own crystal out of alum powder, a salt-like mineral that you can buy at the store. You dissolve it in water, then let it stick to the inside of an eggshell. Your “geodes” might be as glittery as the one Nature makes!

*Wee ones:* How many geodes can you count in the bottom photo?

*Little kids:* Each geode uses half an eggshell. If you have 5 eggs, how many geodes can you make (assuming you don’t break any)? *Bonus:* If you’ve made 6 green geodes so far out of your 10 shells, how many blue geodes can you still make?

*Big kids:* If it takes 28 seconds to paint the inside of an eggshell with glue, then 13 seconds to sprinkle alum powder, how fast can you prep 1 shell? *Bonus:* You then let the eggshells sit overnight in water mixed with food dye and more alum. If they start at 7:00 pm and finish 15 hours later, what time do they come out?

*The sky’s the limit:* If you make 5 geodes all of different colors, then take out 2 in the morning, how many possible pairs of colors could you pick? (Don’t worry about the order in which you pick them — a pair is a pair.)

Answers:

*Wee ones:* We see 7, including the ones peeking from underneath.

*Little kids:* 10 geodes. *Bonus:* 4 blue geodes.

*Big kids:* 41 seconds. *Bonus:* At 10:00 am.

*The sky’s the limit:* 10 possible pairs. If you make blue, green, purple, red and yellow (BGPR and Y) and choose blue, there are 4 other choices you could choose, giving BG, BP, BR and BY. If you choose green as one, then there are only 3 other new choices, since you already counted the blue-green pair. If you choose purple, there are similarly only 2 new choices left, and if you pick red, just 1 more choice (yellow). 4+3+2+1 = 10.

Laura Bilodeau Overdeck is founder and president of Bedtime Math Foundation. Her goal is to make math as playful for kids as it was for her when she was a child. Her mom had Laura baking before she could walk, and her dad had her using power tools at a very unsafe age, measuring lengths, widths and angles in the process. Armed with this early love of numbers, Laura went on to get a BA in astrophysics from Princeton University, and an MBA from the Wharton School of Business; she continues to star-gaze today. Laura’s other interests include her three lively children, chocolate, extreme vehicles, and Lego Mindstorms.