i remember earlier someone talking about a soul gem called azures star. it does exist and is part of a shrine quest i wont say which one it is (for the people that dont wanna know). but the azures star is the item you gain for completing the quest. it is a reusable soul gem. for those who wanna know what the azures star is

So that is what it is use for, I nearly want to sell it to the Creeper. ;)

thanks for telling.