Final Fantasy XII Doubts

So, im new here, and i joind because i bought the game like a weak ago. Ive played some other final fantasy games (VII-VII-X and Tactics) But this is totaly new and i just love it, theres no more to it. SHame i dont have much time to play it…
The thing is, so far in the game i have two questions that i hope some one can answer.
First, the stones the the fiends drop are usefull for something? or i can just sell them all?
And second… (i may spoil the game here so if you just start you are worned!) Im heading to the kings tumb to get a prof of ashes right to the throne, beyond the sandsea. This muggle told me that if i deafetat a tortoide i could claim a tresure, i did but i have no idea were it is, can anyone help me?

Thanks!

PS: Sorry for the gramar mistakes, im from argentina and im still learning.

double post… bad boy

double post… bad boy

My bad…