06: Rocks : Icse-ix-geography

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Qstn #2
Name any three elements of the earth’s crust.
Ans : These are silicon, aluminium, iron, magnesium, calcium, potassium, sodium and nickel.

Qstn #3
Name three types of rocks.
Ans : Three types of rocks are sedimentary, igneous and metamorphic rocks.

Qstn #4
Why are the igneous rocks also called the primary rocks?
Ans : The igneous rocks were the first to be formed. They form the basis of formation of other types of rocks. Thus, they are called primary rocks.

Give one difference between Extrusive igneous and Intrusive igneous rocks.

Ans :

Extrusive igneous rocks	Intrusive igneous rocks
These rocks are formed by the cooling of molten magma on the earth’s surface.	These rocks are formed when the magma solidifies within the earth’s crust forming coarse texture.

Qstn #6
Name any two chief characteristics of Igneous Rocks.
Ans : Igneous rocks are formed by cooling of magma and these are crystalline rocks and full of mineral compounds.

Qstn #7
What is the main characteristics of Basic Igneous Rocks?
Ans : Basic igneous rocks have higher percentage of oxides of denser elements and dark in colour.
Example: Basalt, dolerite etc.

Qstn #8
Name two important landforms made by Igneous Rocks.
Ans : Conical mountains and extensive lava plateaus.

Qstn #9
What are Sills ?
Ans : The magma takes place in between the layers of rocks and hardens after cooling, which is called Sill.

Qstn #10
Which rocks are associated with ores of metals ?
Ans : Igneous rocks are associated with ores of metals due to their origin by cooling magma resulting in crystalline rocks rich in mineral content.

Qstn #11
Which rocks are associated with fossil fuels ?
Ans : Sedimentary rocks are associated with fossil fuels due to fossils trapped in between layers of these rocks.

Qstn #12
Mention any two chief characteristics of Sedimentary Rocks.
Ans : Sedimentary rocks are formed from material derived from other rocks including plant and animal remains. These rocks thus contain fossils.
Sedimentary rocks are generally not crystalline. They are soft and layered as they are formed by deposition of sediments.