Page 86 - Science - 5

w Marble, sandstone and granite are used in the construction of buildings.

w Gems find use in jewellery industry. Diamonds are used for cutting glass.

COAL, PETROLEUM AND NATURAL GAS
Besides metal ores and minerals, the Earth’s crust also consists of huge

quantities of coal, petroleum and natural gas (methane). Coal, petroleum and
natural gas are major sources of energy.

Coal
Coal
Coal
About 300,000,000 years ago, much of the
Earth’s surface was covered with dense forests

and swamps. As trees and other plants died
and fell, they did not decay completely. Airless

mud and certain other conditions made it
difficult for decayed bacteria to live. So, the

Coal half-rotten trees gradually sank into the mud.

More and more dead vegetation and sediments are collected on top of them.
Over the years, these sediments under high pressure and heat formed coal.
Uses of Coal

Coal is used :
w in power stations to generate electricity.

w to make drugs, plastics, cosmetics and fertilizers.
w as a fuel for cooking.
w in blast furnaces in steel industry.
Petroleum
In India coal mines are situated in Jharia
(Jharkhand), Raniganj (West Bengal), Singareni, Dhanbad and Neyveli.

Petroleum
Petroleum
Petroleum
Petroleum gets its name from the Latin words petra and oleum . Petra
means rock and oleum means oil . It is named so, as it is the mineral oil
found in rocks.
Petroleum is formed under the seas. Dead tiny plants, animals and bacteria

sank to the bottom of the sea and get mixed with the sand and silt on the sea
bed. Their bodies did not decay completely but were crushed by the weight of

sediments formed later. Their remains become a mixture of carbon
compounds called petroleum .

Wells are dug deep under the ground to get petroleum. Petroleum is subjected
to fractional distillation to separate various components. This job is done in a

Discover 87 Science/5
87
87