How soil is made up?

The surface of the Earth is covered by a layer of rock. This layer is called the Earth’s crust.

Scientist who study rocks are called geologists.

Rocks

A rock is a naturally occurring solid. It is made of minerals (which are crystalline), or other mineral-like substances. 

The Earth's outer solid layer, the lithosphere, is made of rock. That means the Earth's crust is made of rock.

The different minerals in the rocks make different kinds of rock.

Geologists study a number of different materials that they call rocks.

The photographs below show some different kinds of rocks.

Minerals

Rocks are made up of grains of different materials. These different materials are called minerals. When you look closely at some rocks you can see the different minerals.

Each mineral is made of one chemical substance. In some rocks the minerals form small crystals. In other rocks the crystals are much larger.

This is granite. The glassy crystals are quartz. The large pink and white crystals are feldspar. The small black crystals are mica.

Granite is a rock made from quite large crystals of three different minerals. Granite is sometimes polished and used as flooring or work surfaces because it looks attractive.

The three minerals in granite are called quartz, feldspar and mica.

Soil

Soil is made from tiny rock particles and humus.

Soil is formed when rocks wear down due to weathering. The soil used greatly influences the growth and development of plants.

Soil provides an anchoring medium for many plants and plants absorb water and mineral salts from the soil.

Soil is made up of small particles of rocks and minerals. Soil also contains the remains of plants, animals and waste products such as dung. All the material that comes from living things is called humus.

Many bacteria, fungi and small animals live in the soil. The bacteria and fungi break down the dead plant animal materials.

The particles in soil may be different sizes. Sand particles are large. Clay particles are small. Soils also contain different amounts of humus.

These difference give soils different properties. These properties are important for growing crops.