Elemental Transformation

You imbue a willing creature with a spark of elemental energy determined by the precious stone used in the casting. For the duration the target’s appearance transforms to incorporate the element that the spell is channeling and gains a set of benefits based upon which stone was used:

Air (blue sapphire): The target’s skin turns a light blue and a consistent gust of wind swirls up from beneath them. The target gains resistance to lighting and thunder damage. They also gain a flying speed equal to their walking speed. 
Earth (yellow diamond): The target’s skin turns hard and rocky while crystals grow out of them. The target gains a +2 bonus to AC. They also gain the ability to burrow through nonmagical, unworked earth. While they do so they do not disturb the material they move through. 
Fire (red corundum): The target’s body begins to burn as flames pour across their form. The target gains immunity to fire damage. The targets melee attacks also deal an additional 1D8 fire damage. 
Water (emerald): The target becomes fluid, as their skin turns a dark blue and water constantly drips from them. The target gains resistance to acid and bludgeoning damage and a swimming speed equal to their walking speed. The target is also able to squeeze through gaps as narrow as 1 inch wide without issue.