I assume you mean enchanted with stone striker (not stone sheath, which just prevents critical hits).
Skills trump weapons (so balthazaar and stone striker trump an icy weapon, after all if you had a sundering sword that deals slashing damage, those skills convert the slashing damage to holy/earth damage). As for which skill wins, it is whichever one was applied most reccently.
Whichever was applied last would override the previous one, so if you Put up Avatar of Balthazar and then Stone Sheath, then you'd be dealing earth damage, and verse-vice(sp?) you'd be dealing holy.
Hawkofstorms: I did mean stone sheath. As Lotrfish pointed out, it makes opponents cause earth damage.
So is the general thought that skill trumps weapon mod, and hex trumps skill? Or is it an order of operations type thing, where if the hex is placed, then the form adopted - the form's damage will win out?
IMO (and I haven't tested it, but with a friend in a skirmish it would be easy to do), the hex will always triumph. ANet simply doesn't want you to be able to trump the effect of a hex, they want you to have to remove it to get rid of the bad effect, otherwise, what would be the point?