For polishing stones, the best oil to use is mineral oil. Mineral oil is ideal due to its non-reactive nature, which prevents it from altering the stone's composition. It also has a high flash point, making it safe for use without the risk of spontaneous combustion. According to a study published in the Journal of Gemology, mineral oil is preferred over other oils like olive oil or coconut oil because it does not leave residues or cause discoloration on the stone surface. This is crucial for maintaining the stone's natural luster and appearance.