I am looking for some feedback on a feat I am considering for my wife's Elemental Earth Wizard. She envisions her character manipulating rocks and earth, and using them to damage her opponents. She is not keen on "the earth is acid" idea. I have the old Arcana Unearthed by Monte Cook and we both love how he separated elements from energy. There are feats that let you substitute the original element type for one you specialize in. The Elemental Spell feat in APG is not what we are looking for, as it raises the spells level and uses the "earth is acid" concept.
Here is what I am proposing.
Feat: Elemental Master
Prereqs: Elemental Specialization, Spell Focus (element of specialization)
Benefit: An Elemental specialist Wizard who meets the prereqs. and selects this feat can substitute the element type of any spell she knows when preparing spells for the day. When the spell is cast, it deals damage based on the chosen element instead of the original.
For example: an earth wizard who prepares a fireball spell can choose to prepare it so that it will do earth damage instead. She will effectively create and explosive ball of earth and stone. Burning Hands would shoot out shards of rock, etc.
Complications: I realize there is no damage type [earth] when considering Damage Reduction/Vulnerability.
Note: We are casual, non-competitive gamers who see the rules as guidelines for communal story telling.