How to Make a Geode of Blue Copper Sulfate Crystals

Homemade blue geode crystal

Crystal Titan / Wikimedia Commons / CCA by 4.0 

by Anne Marie Helmenstine, Ph.D.
Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels.
Updated February 12, 2019

Geodes are a type of rock containing crystals. Normally, millions of years are required for flowing water and minerals to deposit crystals. You can make your own 'geode' in only a few days. Grow beautiful translucent blue crystals of copper sulfate pentahydrate inside an egg shell to make your own geode.

This project is of average difficulty and will take 2 to 3 days to finish.

What You Need

Here's How to Do It

  1. First, you need to prepare the eggshell. A natural geode forms inside a mineral. For this project, the mineral is the calcium carbonate of an eggshell. Carefully crack open an egg, discard the egg, and keep the shell. Clean the egg from the shell. Try for a clean break, to create two halves of the shell, or you may wish to just remove the top of the shell, for a more ball-shaped geode.
  2. In a separate container, add copper sulfate to 1/4 cup of hot water. The amount of copper sulfate isn't exact. You want to stir copper sulfate into the water until no more will dissolve. More is not better! It should take a few pinches of solid material to make a saturated solution.
  3. Pour the copper sulfate solution into the eggshell.
  4. Place the eggshell in a location where it can remain undisturbed for 2 to 3 days. You may want to place the eggshell in another container to keep it from falling over.
  5. Observe your geode each day. Crystals should appear by the end of the first day and will be at their best after the second or third day.
  1. You can pour out the solution and allow your geode to dry after a couple of days or you can let the solution fully evaporate (a week or two).

Tips for Making a Geode of Copper Sulfate Crystals

  1. Even a small increase in the temperature of the water will greatly affect the amount of copper sulfate (CuS04 . 5H20) that will dissolve.
  2. Copper sulfate is harmful if swallowed and can irritate skin and mucous membranes. In case of contact, rinse skin with water. If swallowed, give water and call a physician.
  3. Copper sulfate pentahydrate crystals contain water, so if you want to store your finished geode, keep it in a sealed container. Otherwise, water will evaporate from the crystals, leaving them dull and powdery. The gray or greenish powder is the anhydrous form of copper sulfate.
  4. The archaic name for copper (II) sulfate is blue vitriol.
  5. Copper sulfate is used in copper plating, blood tests for anemia, in algicides and fungicides, in textile manufacturing, and as a desiccant.