Here's why:

* Formation: The Twelve Apostles are formed from limestone, a sedimentary rock. Limestone forms from the accumulation of marine organisms' shells and skeletons over millions of years.

* Erosion: The dramatic shapes of the Apostles are due to the erosive power of the ocean. Waves and wind have carved away at the limestone cliffs, leaving behind the iconic stacks.

* Igneous and metamorphic rocks: Igneous rocks are formed from cooled magma or lava. Metamorphic rocks are formed when existing rocks are transformed by heat and pressure. These processes are not involved in the creation of the Twelve Apostles.

Let me know if you have more questions about rocks or geology!