Chemical Gardens and Silicate Chemistry
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Chemical Gardens and Silicate Chemistry

How a simple chemical trick can lead to some very complex studies. This is based on the reaction of certain heavy metal salts with alkali metal silicates

A chemical garden works because the internal pressure of the water of crystallization contained inside the chemical towers is higher then the surrounding free water outside. The chemical tower is composed of a complex precipitate of metal silicate colloids taking a form similar to geopolymers. It is this difference of pressures that causes the chemical towers to grow upward. The material composing the towers is recognized by mineralogists as being chemically similar to several naturally occurring silicate minerals.

The growth of the towers is an analog of a polymer only in this case the reaction is based on silica based radicals rather then carbon based radicals. A similar reaction is found in “geopolymers” that are an alumino-silicate based replacement for Portland cement as a binder for making concrete. In this case we are able to observe the double bonding of silica with metal ions is a free standing reaction rather being enclosed in a matrix with other substances. This reaction is based on the double bonding of the silica atom with two valence metals or above.

Each metal salt in the reaction is able to retain its characteristic color because the speed of reaction is extremely swift not allowing a co-mingling of the various chemicals under normal circumstances. If the concentration of metal salts exceeds the amount of silica atoms it is to react with the excess chemicals precipitate before forming silicates making the sodium silicate solution to become milky. Any of the resulting chemicals produced as chemical towers in the reaction would be able to function as “binders” in the geopolymer process.

Although the reaction calls for the use of a 10% solution of sodium silicate to go forward and of the “alkali” metals can be substituted in the reaction. Although you can buy these chemicals commercially they can all be synthesized by dissolving amorphous finely divided silica in a solution of alkali metal hydroxide. A readily available source of amorphous silica is diatomaceous earth that is used in many places. The ancient Egyptians prepared this by reacting it with sodium hydroxide. When the resulting solution cleared in 10 to 20 minutes what was left behind was a solution of sodium silicate. If you try this be sure that you have pure diatomaceous earth that doesn’t have any Bentonite clay mixed with the DE.

The Chemical Garden is a good teaching tool for studying an introduction to silicate chemistry, geochemistry or mineralogy because it looks so simple in the beginning but has so many ramifications the deeper you dig. Any of the disciplines mentioned is a whole scientific study all by itself.


Handbook of Chemistry & Physics, CRC Publishing, New York, 2008

Make your own Magic Rocks, Anne Marie Helmenstine, chemistry,

Silicon Dioxide, Wikipedia,

Colloid, Wikipedia,

Geopolymer Presentation, John Carter,


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