Classwork Exercise and Series (Geography- SS1): Definition Of Rocks

Definitions of Rock

A rock is any solid substance that forms part of the earth’s crust. Rock is made up of minerals. The most common rocks and their minerals are:

Rocks                                                    Mineral content

Limestone                                           Quartz, micas, feldspar

Sandstone                                          Quartz, Calcite, feldspar

Granite                                                Feldspar, augite

Basalt                                                   Calcite, dolomite

Shale                                                    Quartz, micas, feldspar

   Types of Rocks

Rocks are grouped based on their origin and mode of formation

1. Igneous Rocks: They result from the eruption, cooling and solidification of magma from beneath the earth. They are usually crystalline. There are two types; plutonic (intrusive) igneous rock and volcanic (extrusive) igneous rock. Examples are basalt and granite.

Characteristics of igneous rocks

• Igneous rock are crystalline
• Igneous rock are non stratified
• Igneous rock are hard and impervious
• Igneous rock don’t contain fossils

2. Sedimentary Rocks: sedimentary rocks are formed from the accumulation of sediments by water, ice or wind.

Characteristics of sedimentary rocks

• Sedimentary rock are non crystalline
• Sedimentary rock occur in strata( layers)
• Sedimentary rock contain fossils
• Sedimentary rock are not resistant to erosion

There are three types of sedimentary rocks based on their processes of formation. These are:

Mechanically formed sedimentary rocks are formed from action of water, ice and wind. E.g clay, sandstone, shale etc

Chemically formed sedimentary rock are formed from chemical participation examples are rock salt, gypsum, potash, borax e.t.c

Organically formed sedimentary rocks are formed from the remains of plants and animals examples are chalk and corals

3. Metamorphic Rocks are 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. The original character and appearance may be greatly altered or changed by such forces

Characteristics of Metamorphic rock

• Metamorphic rocks often contain fossils
• Metamorphic rocks have different colours and texture
• Metamorphic rock may be hard or soft

Importance of rock to man

• Rocks are ores containing minerals like gold, diamond, copper, silver, petroleum etc
• Rocks are raw materials for industries example limestone is used in making cement; marble for making and beautifying houses and making of glass
• Rocks are domestically useful; as grinding stones
• Granites are used for constructing work.
• Rock masses on mountain serves as tourism centre example Olumo rock, Zuma rock in Suleja

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