Question

How are Mega Stones depicted in the overworld?

Comments

What do you mean by "depicted"?

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like TMs you find are in Yellow Pokeballs instead of the usual Red ones. I assume thats what he means

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Heres a link mew http://segmentnext.com/2013/10/12/pokemon-x-and-y-mega-stones-locations-guide-how-to-get/ not sure if the information is correct though

Answer 1

Ha I found it, they are shown as purple sparkles in the overworld.

Source P.S. its a full guide by Shofu on where and how to find the megastones.