The Magma Stone is an accessory that can be found pre-hardmode that grants fire damage to most weapons used by the player. Attacking with the stone equipped creates flaming particles similar to the Molten Armor/Weapons and causes melee weapons to inflict the On Fire! debuff.
Because this item adds a visible fire effect to any melee weapons, it produces light. It is a great item to save torches on spelunking trips and dungeon dives.
As a melee accessory, this may not affect any magic or ranged weapons.
This also works with projectiles shot from a melee weapon like the Beam Sword, Ice Blade or others.