STEM Activity: Geology Detective

Go to your local park — or your backyard — and see if you can collect all three types of rocks: igneous, sedimentary and metamorphic! Be a rock detective using white distilled vinegar to discover if your samples contain limestone. Limestone is a type of rock formed from calcium carbonate, often from the remains of marine fossils.

Materials Needed

• Bucket
• Gardening gloves
• Notebook
• Pen or pencil
• Small plastic bowl
• Small shovel
• White distilled vinegar

Step-by-Step Instructions

1. With adult supervision or permission, search in your backyard or nearby park for rocks with different colors, shapes and sizes. Collect your samples in a bucket and be sure to wear a pair of gardening gloves to protect your hands. If a rock is stuck in the ground, a trowel or shovel might help excavate it. Consider wearing safety glasses to protect your eyes.
   
   Be on the lookout for these three types of rocks:

Igneous rocks are formed from melted rock (like lava or magma) deep beneath the Earth’s crust.

Sedimentary rocks are made from many layers of sand, small rocks, and dead plant and animal material, that are compacted underground over time.

Metamorphic rocks are igneous or sedimentary rocks that have been transformed (metamorphosed) through intense underground heat and pressure.

Remember — all kinds of rocks may not be present in all areas!

2. Once you’ve finished collecting your samples, take out your notebook. Tear out small pieces of paper and label each of your samples with a number (sample 1, sample 2, etc.). Then, write these numbers in your notebook.
    
3. Examine each rock, noticing its color, texture and features. In your notebook, take notes on the features of each sample. Predict which rocks contain limestone by writing a big letter “L” next to the sample number. Helpful hint: Limestone can be yellow, white and gray in color, is generally a hard rock and can contain fragments of other rocks and even shells.
    
4. One at a time, place each rock in a small plastic bowl and pour white distilled vinegar over it. Make sure to cover the rock in its entirety.
    
5. After a few minutes, use your observation skills to identify if bubbles are beginning to form. If bubbles form on the surface of the rock, it contains limestone!
    
6. Return to your notebook and count how many of your predictions were correct!

What Are We Discovering?

Limestone is a type of sedimentary rock that contains calcium carbonate. This compound chemically reacts with acids, such as those found in white vinegar (otherwise known as acetic acid). When the calcium carbonate and vinegar react, one product they release is carbon dioxide. This is the same gas that makes bubbles in carbonated beverages! You can see the carbon dioxide as it forms on the surface of the limestone and releases as bubbles into the liquid. To learn more about how beverage bottles keep that carbonation contained, check out National Inventors Hall of Fame® Inductee William Painter, who invented the bottle cap still used to seal carbonated beverage bottles today.

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