ROCK FORMATION: Rock is defined as any solid mineral material of the earth.
TYPES OF ROCK
1. Igneous rock
2. Sedimentary rock
3. Metamorphic rocks
MODE OF IGNEOUS ROCK FORMATION
1. IGNEOUS ROCK: Igneous rocks are formed by the cooling and solidification of molten rocks called magma ejected from beneath the earth’s crust.
TYPES OF IGNEOUS ROCK
i) Plutonic (Or Intrusive) Igneous Rock: This is formed when the molten magma cools and solidifies slowly before it gets to the surface of the earth to form large crystals e.g. granite, gabbro, diorite.
ii) Volcanic (Or Extrusive) Igneous Rocks: These rocks are formed when the molten magma cools and solidifies rapidly on getting to the surface of the earth to form small crystal. An example of volcanic rock is basalt
MODE OF SEDIMENTARY ROCK FORMATION
2. SEDIMENTARY ROCK: Sedimentary rocks are formed from sediments deposited either by water, by wind or by ice. These sediments are accumulated in layers or strata, one on top of the other and after a long period of time, they become hardened by compression to form sedimentary rocks.
TYPES OF SEDIMENTARY ROCKS
i) Mechanically Formed: This is formed from sediments of other rocks that have accumulated and cemented together over a long period of time, example sand store, breccias shale, clay, clay and conglomerate.
ii) Organically Formed Sedimentary Rocks: These rocks are formed from the remains of living organisms, vegetables. Examples include coal, peat, lignite, petroleum etc.
iii) Chemically Formed Sedimentary Rocks: They are precipitated chemically from rock solutions. Example include potash, sodium, chloride (common salt), nitrate, gypsum and dolomite.
3. METAMORPHIC ROCK: This is known as changed rocks. The rocks are formed from pre-existing igneous or sedimentary rocks which have been changed as a result of great heat and pressure. Examples are slate, marble, quartzite, gneiss, schist and graphite.