Mini Me Geology Blog

Many rocks can look alike which makes testing each sample an important part of the identification process. Sometimes telling the difference between limestone, marble, and other similar rocks such as shale and quartzite can be difficult. The fizz test for limestone and marble rocks is a favorite among geologists as a quick way to begin the rock identification process.

Calcite is the main component of limestone rocks and its varieties like oolitic limestone, fossiliferous limestone, coquina, and metamorphic rocks like marble. The calcite mineral is made of calcium carbonate which reacts with acid. Other varieties of calcium carbonate minerals such as aragonite and dolomite will also fizz during this test.

How to Perform the Geology Fizz Test for Limestone and Marble

You will need:

• Acid (hydrochloric or household acid such as lemon juice or vinegar)
• Minerals and rocks to test
• Eye dropper or straws
• Hand magnifier
• Paperclip or knife
• Notebook
• Pencil
• Camera (optional)

Step 1: Gather the samples you want to test. Some good choices are limestone, oolitic limestone, coquina, and marble. You should see some “fizzing” with these samples.

Step 2: Create a fresh surface for the test by breaking the sample in half or using the paperclip or knife to scratch the surface, removing the outer weathered material.

Step 3: Using a straw or dropper place a few drops of acid on one of your rock and mineral sample at a time.

Step 4: Look through your hand magnifier right away to see the bubbles. The bubbles may be small so look closely.

Step 5: Observe and document your results. Do you see the bubbles? If so, what do they look like? The fizz is telling you that your rock contains calcium carbonate.

Teacher and Parent Tip: Use other samples such as shale, slate, and quartzite to observe samples that should not “fizz.” Mix up your samples and see if you can identify them using the fizz test! If you have access to hydrochloric acid, it provides the best reaction with calcium carbonate but children should only use this acid under strict supervision. Creating a fresh surface for the test will help the bubble appear bigger when using lemon juice or vinegar.

You can find more great activities like these in our Rock Cycle Kit and Rock Detectives Kits! Our My Rockin’ Collection Junior Sedimentary Rocks will teach you about several varieties of limestone that fizz!

Filed under: Geology / Earth Science, Rocks - Igneous, Sedimentary & Metamorphic on April 28th, 2014