Rocks And Minerals

Rocks of different kinds are found all over the earth in hills and mountains,in the soil and under the ground.Huge rocks found on mountains are called boulders.The tiny grey stones or gravel used to build roads are also rocks.Sand is made up of tiny pieces or particles of rock.When rocks break up into tiny particles they form soil.Scientists who study rocks are called geologists.

Rocks are divided into three groups depending on how they are formed.Igneous rock- Deep inside the earth it is so hot that all substances melt.The central part or core of the earth contains a mixture of molten rock and gases.This is called Magma.Sometimes magma is pushed upwards by the heavy rocks all around it.When it finally reaches the earth's surface it escapes through a little crack or hole in the ground.As they cool they collect around the crack and form a mountain.this kind of mountain is called a volcano.The molten rock called lava continues to flow out of the crater of the volcano.As it cools it hardens into a rock called igneous rock.It means made from fire and heat.When magma cools slowly under the ground it turns into another rock called granite.Pumice is another igneous rock.It is very light and has many holes.Sedimentary rock-Rivers flowing down to the sea carry with them soil,sand and pieces of rock.In the sea these heavy materials sink to the bottom.they settle there and are called sediment.Each year new layers of sediment form on top of the older layers.This goes on for thousands of years.The enormous weight of the upper layers and the water press down on the lower layers.These lower layers harden and form sedimentary rock.Conglomerate is a kind of sedimentary rock containing pebbles,gravel and sand.It is formed when the lowest layers of sediment harden into rock.Sandstone is formed when layers of sand harden into rock.It is often pink or reddish in colour.Metamorphic rock- The word metamorphic means to have been changed.These are those rocks which began as either sedimentary or igneous rock and were changed into another kind.The new rocks are often different in their form and colour.Limestone changes because of these reasons into a hard stone called marble.Soft shale is changed into a hard smooth metamorphic rock called slate.Slate is used for the roofs of buildings.

Mineral- It is a chemical substance found in nature.Many rocks and minerals are found togther.Some rocks are dug out of the ground in quarries.Most mineral ores ha ve to be mined from under the ground.Important substances obtained by mining include metals ( iron,copper,silver,lead and gold),gems,coal and petroleum.