A Glass Staff

This Staff of Defense is made of glass yet is as strong as oak, weighing three pounds. While holding the staff:
{1} You have +1 to AC
{2} The staff has 10 charges (recharged 1d6+4 per day) that can be used for mage armor (1 charge)
or shield (2 charges)
{3} +1 to hit; +1 to damage
{4} If you expend the last charge roll a d20; on a
20 it explodes doing 2d6 in a 30 foot radius