We’re slowly working our way through all the classic science experiments for kids. Epsom salt crystals are a favorite version of crystal experiments that everyone should try at least once!
Use this tutorial to learn how to make Epsom salt crystals.
It’s possible to make really big Epsom salt crystals if you create a highly supersaturated solution and cool it quickly, plus leave it for a long time. Saturation, temperature, and time are the secrets to making huge Epsom salt crystal gardens!
Keep reading to learn how to make your own Epsom salt crystal garden.
This post is part of the 31 days of creative STEM activities for kids series.
How to Make Epsom Salt Crystals
Follow along with these step-by-step directions for making crystals from Epsom salt!
Find more classic science fair projects here.
You’ll also want to check out the ultimate list of summer STEM activities and the ultimate list of summer science experiments.
Epsom Salt Crystals Facts
Epsom salt is another name for magnesium sulfate.
The natural form of Epsom salt (MgSO4) is a mineral called epsomite.
Epsom salt is also found on other planets like Mars and Ceres.
The hotter water is, the more magnesium sulfate can bind with the water molecules because everything is moving around fast.
When you heat water and stir in Epsom salt, the water absorbs the magnesium sulfate.
However, when the mixture is refrigerated, the magnesium sulfate atoms pull away from the water and form a crystal structure because the water can no longer hold all of the Epsom salt.
Why does Epsom salt make crystal spikes?
As the water cools, the water can’t hold as much salt. So it releases it, and because there is a seed crystal in the container, the Epsom salt crystals form around that.
Epsom salt forms a cylindrical, spiky shape due to it’s molecular structure.
It looks like this:
How long do Epsom salt crystals last?
An Epsom salt crystal can last a long time if left undisturbed. However, they are super fragile, so they are likely to break easily and can crumble.
If an Epsom salt crystal gets wet, it will dissolve.
If you store Epsom salt crystals in a dry, safe spot, they can last for years!
Epsom Salt Crystals Supplies
Shop the Amazon affiliate links below for supplies you may not have for your crystal science experiment.
- Epsom salt
- Food coloring
- Something for the crystals to “stick” to (another Epsom salt chunk will work fine)
- Container for the Epsom salt crystals
Epsom Salt Science Experiment Directions
Follow along with these easy directions to learn how to make Epsom salt crystals! Kids will love this super fun, super easy science activity.
Stir about 1/2 a cup of Epsom salt into 1/2 a cup of hot tap water (but not boiling).
Tap water is better than filtered water for this project because more impurities make better crystals. Not all of the Epsom salt will absorb, but most will.
Add some food coloring and a few pieces of impurities (you don’t have to use toast crumbs) and pour it into your container.
Stick the mixture in the freezer for about 10 minutes to rapidly cool, then stick it in the refrigerator overnight.
Epsom Salt Crystal Results
The next morning, you should see that crystals have formed (if they didn’t, your mixture didn’t have enough impurities or you didn’t mix enough Epsom salt into the liquid).
Pour off the extra water to examine your crystals. If you leave them in the liquid long, they will start to melt.
Our Epsom salt crystals started to melt about 5 minutes after we removed them from the refrigerator even though we did pour the extra liquid off. Perhaps we didn’t have quite enough Epsom salt in the mixture?
To make this more like a real experiment rather than a demonstration, you could try mixing several batches of salt with different quantities of salt.
Or try seeing if crystals form better in the refrigerator, freezer (but not long enough for the water to freeze), or at room temperature.
More Crystal Science Experiments
Super Fun and Easy Crystal Science Fair Projects
How to Make Crystals without Borax
How to Make Salt Crystal Feathers (in under an hour!)