Rocks are natural materials made from minerals, fragments, or other geological constituents. They form much of the solid ground beneath soil, water, and vegetation. A rock can look uniform at first glance while containing grains, layers, or structures that reveal a more complicated history. Differences in these features help explain why rocks respond differently to water, weathering, pressure, and the passage of time.
One broad way of describing rocks is by how they formed. Igneous rocks develop from cooling molten material. Sedimentary rocks form through the accumulation and later alteration of material deposited at the surface or in water. Metamorphic rocks develop when existing rock changes under conditions such as increased heat or pressure. These categories describe origins, although later events can add further complexity to an individual example.
The texture of a rock includes the size, shape, and arrangement of its components. Large visible crystals suggest conditions different from those represented by a very fine-grained material. Layers may record successive episodes of deposition, while cracks or folded structures can indicate later movement. Colour can also be informative, but it is not a complete guide by itself. Weathered outer surfaces may look different from freshly exposed material inside.
At the surface, rocks interact with air, water, living organisms, and changing temperatures. Some minerals alter chemically, while physical processes can break larger pieces into smaller fragments. Gravity and moving water transport these fragments into new settings. A pebble in a stream may therefore have a history that began far from the place where it is now found, linking separate parts of a landscape through movement and erosion.
Observation can start with ordinary details: the outline of a grain, the direction of a layer, or the contrast between a sheltered and an exposed surface. Comparing several examples is often more useful than assigning a name from colour alone. Rocks are not merely a background to the visible world; they preserve evidence of formation, change, and transport, connecting present-day landforms with processes operating over many different timescales.