Rocks and soils

Introduction

Characteristics of rocks

Some rocks are harder than others. For example, granite is a very hard rock, but chalk is a very soft rock and wears away easily.

Some rocks, such as sandstone or chalk, let water soak through them. They are called permeable rocks.

Other rocks, such as marble and slate, do not let water soak through them. They are called mpermeable rocks.

Uses of rocks

Slate

Because slate is a hard, impermeable rock, which splits easily into thin sheets, it is ideal for making roofing tiles.

Marble

Marble has an attractive texture and colour and can be cut and polished. Because of this, it is used to make floor tiles and wall tiles. Some statues are made from marble too.

Chalk

Chalk is a rock that is formed from the skeletons of tiny sea animals. It wears away very easily which is why it ideal for making sticks of chalk to write on blackboards.

Granite

Granite is a coarse-grained rock that is hard and impermeable. It is often used to make steps and roads as it is a rock that doesn’t wear away easily.

Soils

Soils are a mixture of tiny particles of rock, dead plants and animals, air and water.

Different plants grow better in different types of soil.

Sandy soil is pale coloured with lots of small air gaps. Water drains through sandy soil easily so it usually feels quite dry.

Clay soil is an orange or blue-ish sticky soil with very few air gaps. Water does not drain through it easily. When it rains, puddles stay on top of clay soil for a long time.

Chalky soil is a light brown soil. Water drains through it quickly.

Peat is different from other soils because it does not contain any rock particles. It is made from very old decayed plants and is dark, crumbly and rich in nutrients (chemicals plants need to grow).