The correct answer is option 'A', igneous rocks. Let's understand why igneous rocks are the most abundant rocks found on Earth's crust.

Igneous Rocks:
Igneous rocks are formed from the solidification and cooling of molten magma or lava. They are classified into two types: intrusive and extrusive. Intrusive igneous rocks cool and solidify beneath the Earth's surface, while extrusive igneous rocks cool and solidify on the Earth's surface.

1. Formation:
Igneous rocks are formed through volcanic activity or the cooling of magma deep within the Earth's crust. When magma is ejected onto the Earth's surface through a volcano, it cools rapidly and forms extrusive igneous rocks. On the other hand, when magma cools and solidifies slowly beneath the Earth's surface, intrusive igneous rocks are formed.

2. Abundance:
Igneous rocks are the most abundant rocks on Earth's crust due to several reasons:

- Magma Generation: The Earth's mantle, which lies beneath the crust, is composed of molten rocks called magma. Magma is generated through processes like melting of subducted crust, partial melting of the mantle, and decompression melting. This continuous generation of magma ensures a constant supply for the formation of igneous rocks.

- Recycling Process: The Earth's tectonic plates are constantly moving, and as a result, older rocks are subducted into the mantle. This process recycles the older rocks, which eventually melt and form new magma. This magma then rises to the surface and solidifies to form igneous rocks.

- Erosion and Weathering: Over time, other types of rocks like sedimentary and metamorphic rocks undergo erosion and weathering. The eroded particles are carried away by water, wind, or ice and eventually accumulate in sedimentary basins. These sediments can then be subducted and melted to form new igneous rocks.

3. Examples:
Some common examples of igneous rocks include granite, basalt, pumice, and obsidian. Granite, in particular, is a widely found igneous rock that is composed of minerals such as quartz, feldspar, and mica.

In conclusion, igneous rocks are the most abundant rocks found on Earth's crust due to the continuous generation of magma, the recycling process of older rocks, and the erosion and weathering of other rock types. This makes igneous rocks a significant component of the Earth's crust.