Ask-a-Geologist #4: Why do geologists tests rocks for calcite?

Why do geologists test rocks for calcite?

We received a great question about why geologists test rocks for the calcite mineral. Let’s jump in!

Why do scientists test rocks to see if they contain the mineral calcite?

This week’s questions from Terence. He wrote to us and asked: “Why do scientists test rocks to see if they contain the mineral calcite?”

Well, Terrence, calcite is a great indicator mineral for rocks such as sedimentary limestones and metamorphic marbles. These rocks are made up of almost entirely calcite. Calcite is made of calcium carbonate and it reacts very strongly with acids like hydrochloric acid and also with some household acids like lemon juice and vinegar. And if you test a rock and it is positive for calcite, it’s a great indication of what your rock sample might be.

How to Test Rocks for Calcite

To test the rock samples, you can pour your acid directly onto the rock surface and look for the fizz or the bubbles to appear. If you’re using a weak acid like lemon juice or vinegar, you might want to use one of these little hand lenses to help you see the bubbles more easily. If you see the bubbles, then you know that your rock definitely has a calcite content and you are well on your way to identifying your rock sample.

Geologists commonly refer to the calcite test as the “Fizz Test.” You can find step-by-step instructions and tips for using lemon juice and vinegar instead of hydrochloric acid on our blog.

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