What Are Rocks Made Of

Rocks are solid materials found all around us on Earth. They are made of one or more minerals, which are natural, nonliving substances that form in the ground. Understanding what rocks are made of helps scientists learn about Earth's history and how our planet changes over time.

Different combinations of minerals create different types of rocks. Some rocks contain just one mineral. For example, marble is made mostly of a single mineral called calcite. Other rocks are made of many minerals mixed together. Granite is a good example of this type of rock. When you look closely at granite, you can see tiny specks of different colors. Each colored speck is a different mineral. Granite usually contains minerals like quartz, feldspar, and mica all mixed together.

When you examine rocks carefully, you can see the minerals inside them. Sometimes minerals appear as tiny grains, which look like small bits of sand stuck together. Other times, minerals form crystals, which have flat surfaces and regular shapes. Some rocks even show layers where different minerals are stacked on top of each other. These visible features help us understand that rocks are really mixtures of natural materials from Earth.

Interesting Fact: The largest crystal ever found was discovered in a cave in Mexico and was longer than a school bus—over 39 feet long!