@Azapuela:
The philosopher stone in many fictions has more powers than just creating gold.
For example:
- the most powerful core to use in an enchanted item - like a protective charm / accessory that protects its holder from any type of damage and harm.
- Puryfing powers
- Absolute healing powers - even the ability to ressurect the dead, sometimes even those who had died ages ago
- Magnifying powers = increasing the power of a spell, a magic, a ritual or simply the holder altogether
- Creating / changing matter beyind just creating gold - in a fantasy world beyond gold there should be even rarer / more powerful things like mythril, adamantium, scarletite/hihirogane
- Sometimes the key to eternal life or/and eternal youth
- Sometimes the key to summon or contact beings from other plaines of existence like demons from the underworld, divine beings from "heaven" or other mythical entities like the 4 sacred/divine beasts
So that stone probably signifies something along those lines.
As such he did not create it for creating gold but to make something out of it - e.g. a broach or a charm for the girl that protects her or increases her magic powers or so.