How to Perform the Geology Fizz Test without Hydrochloric Acid

Geology Fizz Test Experiment for Calcite

Geologists love testing rocks and minerals and, admittedly, one of the most exciting tests is the GEOLOGY FIZZ TEST. The mineral calcite is made of calcium carbonate (CaCO3). Rocks containing calcite, or calcium carbonate, “fizz” when you apply acid to the surface.

How Acid Reacts with Calcite during the Geology Fizz Test

Calcium carbonate reacts with acids and produces carbon dioxide gas, water, and calcium chloride. The carbon dioxide produces bubbles, which look like the fizz on the top of a soda. When you apply acid to the surface of a mineral or rock that contains calcite, you will see bubbles on the surface.

The most common acid that geologists use for the fizz test, is hydrochloric acid. Hydrochloric is a strong acid so it is easy to see the reaction.

Whoa! Hydrochloric Acid Is Too Strong for Kid’s Experiments

We agree that hydrochloric acid is not always the best choice to use with kids. For one thing, when children are learning to identify rocks and minerals you want them to be able to test and explore without worrying if they are going to burn their fingers with a strong acid.

Alternatives to Hydrochloric Acid for Kid’s Geology

Naturally acidic foods are the best choice when children perform the fizz test. Weak acids like lemon juice (citric acid) and vinegar (acetic acid) are the perfect alternatives for performing safe lab experiments with younger kids. The only problem with weak acids like lemon juice and vinegar is that sometimes it is harder to see the reaction (the bubbles).

The best way to fix this problem of bubbles that are too small to easily see is to create a fresh surface on the rock or mineral for the kids to test. There are two ways to create a fresh testing surface on a rock or mineral. The first method is to break the sample open with a rock hammer. The second method is to scratch the surface of the sample with a paper clip. Scratching the surface removes the older, weathered exterior that masks the sample’s true characteristics.

After the children create a fresh surface, they can use a dropper bottle or a straw to place a few drops of lemon juice or vinegar on the surface. If the sample bubbles, there is the mineral calcite in your rock. This is a great test for limestones and marbles which are made completely of calcite. Dolomite, a mineral similar to calcite, is made of calcium magnesium carbonate and will also fizz, but to a lesser extent than calcite.

If you need help teaching kids how to perform the geology fizz test or to identify rocks and minerals using other experiments, check out this book which will provide all of the details you need.


Leave a Reply

You must be logged in to post a comment.