How Rocks Are Different

Rocks are solid materials that make up Earth's surface. Rocks come in many different forms, and scientists describe them by looking at their properties—the characteristics that make each rock special.

One important property is hardness, which means how difficult it is to scratch or break a rock. Some rocks are very hard and cannot be scratched easily. Other rocks are soft enough to scratch with your fingernail. Scientists test hardness by trying to scratch rocks with different tools.

Another property is texture, which describes how a rock feels and looks on its surface. Some rocks feel rough and gritty, like sandpaper. Others feel smooth, like a polished stone. When you look closely at rocks, you might see different structures. Some rocks have visible layers, like stripes of different colors stacked on top of each other. Some rocks have shiny crystals that sparkle in the light. Other rocks look like tiny pebbles cemented or glued together.

Rocks also come in many colors. You can find gray rocks, red rocks, white rocks, black rocks, and brown rocks. Sometimes one rock has several colors mixed together.

Scientists and students sort and compare rocks by testing their hardness, looking at their texture, and observing their color. These properties help us understand and describe the many different types of rocks we find on Earth.

Interesting Fact: The softest rock is called talc, and you can scratch it with your fingernail. The hardest natural material on Earth is diamond, which is so hard it can scratch any other rock!