Stone of Sages

The Stone of Sages, also referred to as the Wisdom Stone, is a hypothetical vessel of stone that can be given shape within Mt. Aleph once the Golden Sun would form above the mountain and enter it once all four Elemental Lighthouses are lit. This stone is never actually seen in the game, but it is described as "dominating everything, it can transmute lead into gold, even thwart death itself". It therefore embodies Alchemy itself, and apparently its mere presence inside the mountain would infuse the world of Weyard with Alchemy's power, keeping the world's life force healthy and allowing for the inhabitants of Weyard to harness the power and knowledge necessary for developing great civilizations.

As indicated by a mind-read at Prox not normally accessible in normal play, the Stone of Sages is a great power source that would prompt the power-hungry to fight for control of the stone. It is likely that this would be a primary plot point in a hypothetical third game in the Golden Sun series, taking place after Golden Sun: The Lost Age (when the Golden Sun is channeled and the Stone of Sages is given shape, thus restoring Alchemy to the world).

It is worth noting that the Stone of Sages never appears in either game as Alex and Isaac absorbed the power of the Golden Sun and so the Stone of Sages was effectively absorbed by the two.