I know a lot of people expect them to be healer cause of the npc appearance but personally I think they'd be either dps caster or melee (they'd be a sort of melee magic wielder) based on their appearance in other ff titles.

To me something makes Geomancers unique visually is their use of vines, plants, water, lava, and sand among other things. Many of them certainly fall under the various elements as far as damage type but are still a refreshing break from the overlapping spell themes of most casters.