[Model Answer QP2022 GS1]Describe the characteristics and types of Primary rocks.

Introduction

Igneous rocks are called Primary rocks. They are called Primary rocks because they are first to form in the geological past of the earth. Also, a primary rock is a rock whose constituents are newly formed (Solidification of Magma or Lava) and have never been constituents of some other rock or formed through replacement and alterations.

These are basically crystalline rocks with no organic remains on them. The examples of primary rocks include Granite, Basalt, and Gabbro.

There are two types of Igneous Rocks:

Plutonic Rocks (Intrusive Rocks)	Extrusive Rocks
1. Solidification of Magma	1. Solidification of Lava
2. Coarse Grained structure because of slow cooling.	2. Fine Grained Structure because of Sudden cooling.
3. The rocks are darker and denser.	3. The rocks are lighter and less dense.
4. Example: Granite	4. Example: Basalt

Characteristics of Primary Rocks:

1. They are unfossiliferous : Any fossils are burnt away due to high temperature. 

2. Texture of the rocks: The grains are either coarse or fine which is reflective of the rate of cooling of magma. 

3. Mineral Rich: Since their origin is directly from the magma, they are rich in minerals especially ferrous minerals.

4. Colour of the rocks: Colour of the rocks reflects its composition. Dark colour usually indicates basic magma as its source and light colour indicates acidic magma.

Conclusion

Primary rocks not only form the core of the continents but also are rocks which are the most mineral rich then sedimentary or metamorphic.