And well, there is no such thing as really just getting a riff and calling it "progressive metal".
Progressive metal is a mindset of how you go about composing music, not so much a style/a type of riffing if that makes sense.
You could easily have played your black metal riff or death metal or thrash riff or even the "metalcore" riff in a progressive metal song and it's still progressive metal, but playing a 20 second snippet of "prog metal" is not progressive metal.