Here's why:

* Formation: Igneous rocks are formed from the cooling and solidification of magma (molten rock) or lava. This process happens deep within the Earth's crust or on the surface during volcanic eruptions.

* Vast Quantities: The Earth's mantle, which is primarily composed of molten rock, is a huge source of igneous material.

* Continual Creation: Igneous rocks are constantly being formed through ongoing volcanic activity.

While sedimentary rocks like sandstone and limestone are also common, they are formed from the weathering and erosion of existing rocks, including igneous rocks. Metamorphic rocks are formed from the transformation of existing igneous, sedimentary, or other metamorphic rocks due to heat and pressure.

Therefore, igneous rock, being the foundation upon which other rock types are built, is considered the most abundant type on Earth.