Question

Consider the following statements:

1.Acid igneous rocks are less dense and lighter in colour.

2.Basic igneous rocks are denser and darker in colour.

Select the correct answer from the following codes

• A. Only 1
• B. Only 2
• C. Both 1 and 2
• D. Neither 1 nor 2

Answer 1

Answer:

C. Both 1 and 2

Igneous rocks

• They are formed by the cooling of magma.

• These rocks are formed by the solidification of lava.

• They are called igneous rocks because they are created by intense heat.

• They can form on or below the Earth's surface, either by crystallization or not.

• Magma is formed by the partial melting of rocks in the Earth's crust or mantle.

• Magma is usually formed for three reasons: an increase in temperature, a decrease in pressure, and a change in composition.

• There are more than 700 types of igneous rocks.

• Most of these are found below the Earth's surface.
  

• Acid igneous rocks are less dense and less colorful.

• They have a higher silica content (usually 65-85%).

• They are mainly composed of light-colored minerals such as quartz and feldspar. Therefore, they are light in color.

• Ex: Granite
  

• Basic igneous rocks are dense and dark in color.

• They are low in silica (usually 45-60%) and high in magnesium and iron.

• They are mainly composed of dark-colored minerals such as pyroxene and olivine. Therefore, they are dark in color.

• Ex: Basalt