Concept:
Ashokan pillars are among the most important examples of Mauryan art and architecture.
They are famous for their polished surface, monolithic form, and animal capitals.
Step 1: Understand Ashokan pillars.
Ashokan pillars were erected by Emperor Ashoka.
They carried inscriptions spreading messages of Dhamma.
They were made with great skill and had a highly polished surface.
Step 2: Identify the stone used.
The Ashokan pillars were generally made of Chunar sandstone.
Chunar sandstone was known for its quality and was used in Mauryan sculpture and pillar making.
Step 3: Final conclusion.
Therefore, the correct answer is:
\[
\boxed{\text{Chunar Sandstone}}
\]