The Stone Golem, also known as RockGol, is an enemy in the original Final Fantasy. Like other Golems, it is resistant to all status effects and elements. Physical attacks are best, despite the enemy's armored appearance.
If not dealt with quickly, fights with it can actually drag on, since it can cast Slow and reduce your party's attack rate. Regardless of whether you choose to engage it physically or with magic, it is best to deal with it quickly as a result. Fortunately, it's somewhat weak for how late in the game it appears.