Ioun stone price check

[Incurable]

Hello, I'm a brand new player and I found a "Vibrant Purple Ioun Stone" today in waterworks. I wasn't sure what it was for so i asked in advice channel and people started offering me, what seems like a fortune, to a new player. But someone else advised me to post it on here and ask for advice, hence this thread. people have offered from 800plat, saying that it was worthless, up to 500,000 plat from a very nice lvl 20.

Might there be anyone who could clear this up for me? I don't fully understand what it is that i have nor what it is truly worth.

Thanks,
~Inky