rocks of the earth

LESSON 13: ROCKS

A rock is the nonliving solid path of the earth crust that contains minerals. They are classified based on their mode of formation there are 3 types namely; Igneous, Sedimentary and Metamorphic rocks

Igneous Rock:

These are rocks formed by the cooling and solidification of molten material (magma) within the earth crust and on the earth crust. Crystals are formed during the cooling of the molten material hence the rocks are also called CRYSTAL ROCKS. It made up 95% of the earth crust; there are 2main types of igneous

Plutonic rocks: They are also called instructive rocks because they result from the solidification of molten magma within the earth surface, this gradual cooling and solidification result to the formation of large and easy recognizable crystals .E.G granite, diorite, dolerite and gabbro.
Volcanic Rocks: They are also called extrusive rocks. They are formed when molten rocks called lava are poured onto the earth surface where it quickly cool and solidifies this result to the formation of fine crystals. E.G basalt, rhyolite, andesite and trachyte.

Sedimentary Rocks:

They are formed from pieces of materials such as bits of rocks, death remain of animals and plants carried and deposited by water, ice or wind on land surface were they are hardened. Sedimentary rocks are formed with the help of compression forces. Sedimentary rocks are classified into 3 bases on their formation mode

Mechanically formed sedimentary rocks: They are formed from the deposition and hardening influence by compression of weathered particles. E.G sand Clair. They are mostly found in lowlands and depressions.
Chemical formed :They are formed when salty solution are been dehydrated when it reaches the earth surface thus leaving the salt which accumulate forming rocks E.G rock salt
Organically formed: They are formed from the accumulation of death remains of plants and animals over a long period of time E.G lime stone from shells and skeletons of animals, coal from death remains of plants.

Metamorphic Rocks:

These are rocks formed from the changing of original structure and forms of other rocks by heat or pressure. Igneous and sedimentary rocks can be change into metamorphic rocks

Original forms	Metamorphic forms
Lime stone	Marble
Granite	Gneiss
Coal	Graphite

ROCK CYCLE

It is an ever ending process by which rocks changes from one form to another

Igneous rocks are formed from the pulling and hardening of magma from the interior of the earth
During weathering this rocks are broken down and the particles are deposited into layers
With time particles are hardened and cemented forming sedimentary rocks
When heat and pressure act on sedimentary rocks they change into metamorphic rocks
If these rocks are hardly heated they will melt to magma which may rise out and cool forming igneous rock
They rock cycle then begins again for millions of years