EM - Rocks and minerals and their exploitation 1.1, page no 1-5

Formation of rocks

• The third rocky planet from the sun:

• The earth is a rocky planet, compared with Jupiter, which is a gas giant.

• The earth is made from metal ores.

• The planet was formed about 4.5 billion years ago. The force of gravity pulled the heavier elements together first, forming the core.

• The lighter elements then formed the earth's crust about 3-4 billion years ago.

TYPES OF ROCKS:

1. Igneous rock

2. ,Sedimentarty rock,

3. Metamorphic rocks.

Igneous rocks:

• The word igneous is latin for fire.

• These rocks form when hot molten rock crystallizes and solidifies.

• Made from liquid magma.

• Magma cools to form solid rock.

• Minerals crystals sometimes present; the size of the crystals depends on the speed of cooling.

• No fossils present.

Sedimentary rocks:Theses rocks are formed from pre-exiting rocks or pieces of once-living organisms.They form deposits that accumalate on the earth's surface.

*Made from other rock fragments.

*Rock fragments become buried and increased pressure forms rocks.

*crystals absent.

*Fossils may be present.

Metamorphic rock:started out as some other type of rock, but have been substantially changed from their original igneous, sedimentary, or earlier metamorphic form. Metamorphic rocks form when rocks are subjected to high heat, high pressure, hot mineral-rich fluids or, more commonly, some combination of these factors.

*Made from existing rock.

*The original rock is changed in form by heat and pressure.

*Mineral crystals present.

*No fossils present.

THE END