678 Possible Answer

Though the phenomenon appeared to be a simple transfiguration spell, the meaning behind it was not so.

Countless powerful mages and sages had already studied the art of transforming objects since ancient times—to convert 'all things' into gold was actually the ultimate goal of the origins for alchemy, its greatest feat being to produce gold and Elixir of Life, the 'Philosopher's Stone' that provides immortality.

Not too long ago, Helm had incinerated its own body and soul so its particles could be accelerated to the extreme to bombard Joshua's body, stopping short of emulating a burst of supernova and producing heavy metals including gold. This transfiguration spell, however, could turn stones into pigeons, with the reverse holding true as well. But if that could be accomplished, it would not be unusual to turn stone into gold.