User blog comment:FairyRaven/Fairy Tail Chapter 331: Natsu's Strategy, Review and Commentary/@comment-3290324-20130517205151/@comment-1776824-20130518172500

I just said it repels all non-Dragon Slayer forms of Magic. Mirajane used Magic to try and hurt Zirconis. It's like hitting a boulder with your fist; you can hit it all you want, but it won't do anything in the long term other than hurt you. Also, it's Gravity Magic, which means that it is a purely Magical source. Gravity Change works in a similar manner, as it can affect the caster as well, but in the end, it's still just Magic. :/