Kids, have you discovered the colorful rocks that grow into underwater stalagmites yet? The ingredients for making your own silicate or crystal garden are a bit too exotic for you to find around the house or in the grocery store. Your best bet is to go to your favorite toy store and look for a product from Craft House called “Magic Rocks”.
Please note: All chemicals and experiments can entail an element of risk, and no experiments should be performed without proper adult supervision.
Follow the instructions very carefully. In fact, they say that an adult partner is needed if you are not 10 years old yet. We’ll give you a bit more of a scientific explanation here of what you’ll observe happening. You’ll first place the “magic rocks” into the bottom of a container and then pour a “magic solution” over them. The rocks are actually chunks of chemicals such as iron chloride (FeCl3), cobalt chloride (CoCl2), copper sulfate (CuSO4), manganese sulfate (MnSO4), and iron sulfate (Fe3(SO4)2). Chemists call compounds like these transition metal salts. They are indeed salts but they are not edible so don’t even think about it! The colors of these particular salts are, respectively, yellow, purple, blue, pale pink, and green. There might be different salts, and therefore different colors, in your set. These are just examples. The solution is sodium silicate, also sometimes called “water glass”. What you are making is a structural precipitate and they are quite complex. The iron chloride salt, for example, changes by chemical reaction with the sodium silicate to a mixture of iron silicates and iron hydroxide. This mixture is gel-like. But the gels will change their texture to become more crystalline and brittle after a while.
An air bubble usually caps the slender shoots that form at first, so look carefully. They move jerkily, from one side to another. An elastic gel-like membrane is actually forming and breaking here.
If your set doesn’t seem to work very well it might mean that the sodium silicate solution has degraded a little bit, especially if the set is old. Most transition metal salts shouldn’t be affected by time, though.
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Kathleen Carrado Gregar, PhD, Argonne National Labs
[email protected]
November 2000
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References:
- T. H. Hazlehurst, J. Chem. Ed. 1941, p. 286.
- B. Z. Shakhashiri, “Chemical Demos: A Handbook for Teachers of Chemistry”, 1983, Vol. 3, p. 379.
