spirit stone : accessory (not hair accessory)

Hi,
I searched the forum but didn't find an answer.
What are those stones for? Cannot be used on jules,boss jules,hair accessory, and also not on weapons even tho in description sais they are for weapon augmentation.
Anyone knows an actual fact about what they are for?

I wait for answer.

Thanks.

You can only use them on "normal" jewelry.
Twilight, Seraph, Eternal etc.

CoC jewelry, boss jewelry etc. will not work