Gem earth and stone

This fist sized emerald gleams with smoldering power.  It fits perfectly into the Staff of Ruin.
Property (Attuned): You must be a wizard to become attuned to this item.
This stone has seven charges.  As an action, you can expend a charge to cast one of the following spells contained in the staff: 
• passwall
• move earth
If you expend the wand’s last charge, roll a d20. On a 1, the wand blackens and crumbles to dust, forever destroyed.
The wand regains 1d6 + 1 expended charges each day at dawn.