The pillars of Ashoka were usually made of:

Most Ashokan pillars were made of a fine, buff-coloured sandstone, mostly quarried at Chunar, near Varanasi in Uttar Pradesh.

About the Ashokan pillars:

• They were erected by Emperor Ashoka in the 3rd century BCE across his empire.
• Many of them carry inscriptions (edicts) that spread his message of Dhamma.
• Each pillar was carved from a single piece of stone (monolithic), and was about 12 to 15 metres high, weighing up to 50 tonnes.
• The pillars were transported over long distances from the quarries, probably on rollers and by river, to places hundreds of kilometres away.

Features of Mauryan pillars:

• They have a very high polish, which makes them shine like metal; this "Mauryan polish" is a hallmark of Mauryan art.
• They have no base; they were set directly into the ground.
• The shaft is plain and slightly tapering.
• On top is a capital, usually with an inverted lotus (bell-shaped) design, an abacus (a slab, often decorated with animals and wheels), and a sculpted animal (such as a lion or an elephant) at the top.

Famous Ashokan pillars:

• Sarnath (Uttar Pradesh): with the famous lion capital, which became the National Emblem of India.
• Lauriya Nandangarh (Bihar): with a single lion on top, still standing.
• Vaishali (Bihar): with a single lion.
• Sanchi (Madhya Pradesh): with a lion capital (broken).
• Sankissa (Uttar Pradesh): with an elephant capital.
• Two pillars from Topra and Meerut were later moved to Delhi by a Sultan of the 14th century.

Other features:

Some scholars see Persian (Achaemenid) influence in the bell-shaped capitals and the polish, while others stress their Indian character.

Why not the other options?

• ✗Granite was used for some later monuments, such as the Gomateshwara statue.
• ✗Marble was used in later Mughal buildings.
• ✗Basalt was used for rock-cut caves in the Deccan.