I'm playing X, and my friend on Omega Ruby wants to give me a Latiosite. Can he give it to me?
The Latiosite and the Latiasite can be traded between X/Y and OR/AS
Source: Literally just did it a minute ago
Because mega stones can't be traded because there is only 1 in each game and also mega latios doesn't exist in x and y so there fore you will not be allowed.