Wizard gains a new innate weapon, the "Spellwand." It attacks using the (ranged) Spell Combat tree. It initially comes into being "unloaded."
The Wizard "reloads" the wand by using any offensive (i.e., non-aura, non-buff) spellgem. Reloading costs 1 AP and 5 MP and can be done at any time (though any existing charges in the Spellwand are lost at the time of reloading). When a spellgem is "reloaded" into the Spellwand, the gem is drained of charges (but not destroyed). The Spellwand takes on the damage type of the spell in the original spellgem, and gains a number of charges equal to 3x the number of charges originally in the spellgem. In this sense Spellgems are just glorified ammo that determine the damage amount and type, nothing else.
The damage done by a spell in a spellwand is equal to the amount that the character would "normally" do in combat if casting the spell spontaneously (i.e., it includes bonuses for knowing similar spells, Fortify Spell, and so forth) though this amount is set as of the time the gem is "reloaded" into the wand (i.e., learning a spell of the same damage type does not increase the damage done by an already-loaded wand, though it will increase the damage done the next time the wand is reloaded). Casting a spell from the Spellwand is done from the regular "combat" menu (which means it can be used against doors, fortifications, etc.). The attack costs the Wizard 1 MP and 1 AP.
Deep Spellcraft and other similar abilities may not be used with Spellwands; i.e., the Spellwand is a "weapon" and not a "spell" for the purposes of abilities that improve attacks.