http://typemoon.wikia.com/wiki/List_of_Magic_Spells#Elemental_Magecraft

That page lists petrification magic as an earth spell (the only earth spell, somehow). I mostly just added it for thematic reasons, so I have no issues with getting rid of it. Like I said, though, mages can resist it by running mana through their circuits. I guess a Servant without Magic Resistance could be affected, but I feel like servants in general are too "epic" to be tripped up by the debuffs of modern mages.