Why do the ponies use crystals to represent magic?

[Discord the Amazing 12]

I dunno if anyone wrote this (or cared to look because it would be to hard to browse through so many subjects when a helpful pony can give me a link to it)

Why did they begin using crystals to symbolize magic again when Twilight already figured it out and if theorized if sunny dose have her journal, would she have known that?

again there is so many contradictions and no answers, how long will it take before even this simple answer is given?

I only say this because they put G5 in G4s universe and to me if it doesn’t pay homage that it’s due then it shouldn’t have been made to begin with, why? Because it’s already a good story and to add on to G4s greatness is to stain it, but that’s just my opinion you can take it or leave it