Rocks

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Types of sedimentary rocks

CLASTIC ROCKS

made of fragments of rock cemented together e.g. Breccia

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2. NON-CLASTIC

Minerals crystallize out of solution to become rock e.g. limestone

Or are formed from remains of plants and animals (also referred to as biogenic rocks) e.g. coal

A. Limestone B. Coal

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Characteristics of sedimentary rocks

May contain fossils

Are stratified

They are not banded

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Metamorphic rocks

Metamorphism means to change.

Rocks change with temperature

and pressure.

Usually takes place deep in

the Earth

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Contact Metamorphism– Rocks are heated by nearby magma (affects a small scale)

Increased temperature changes the composition of the rock, old minerals are changed into new ones

Hornfel is a fine-grained non-foliated metamorphic rock produced by contact metamorphism

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Regional metamorphism: affects a large area and results from plate tectonics

Rocks are changed due to pressure

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Metamorphic rocks can be foliated, i.e. showing layers/bands of minerals e.g. Gneiss or non- foliated e.g. Marble

A. Gneiss B. Marble

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Characteristics of metamorphic rocks

May be foliated/banded

Rarely contain fossils

React with acids

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The rock cycle

Rocks change from one form to another, any type of rock can change into another type, for instance, an igneous rock into sedimentary or metamorphic and vice versa.

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Uses of rocks

Source of minerals e.g. gold

Used in construction

As aquifers, they are good sources of water

They form mountains, which are places of scenic beauty e.g. Mulanje mountain