Rocks and Soils

Rocks are the solid materials that make up the Earth’s crust, and they come in three main types depending on how they were formed. Igneous rocks (like granite and basalt) form when magma from inside the Earth cools and hardens. Sedimentary rocks (like sandstone and limestone) form when layers of sediment — tiny particles of rock, shells and organic material — are compressed together over millions of years. Metamorphic rocks (like marble and slate) are rocks that have been changed by extreme heat or pressure. Over time, rocks are broken down by wind, water and temperature changes — a process called weathering. The tiny particles produced, mixed with decomposed plant and animal matter (called humus), form soil. Different soils have different properties — sandy soil drains quickly, while clay soil holds water.