The thing eduan noted at the time was the light shown when rak used his ability. And after that folk have been surprised at rak simply being able to control the environment. The element or shape are probably not particularly unique but rather the way in which rak manipulates rocks. I am not sure of how what rak does would be different from someone else who has the ability to manipulate rocks. I've speculated that conventionally rankers can't control the elements around them but that sounds strange considering shinsoo combat is based around gathering shinsoo from the environment..
evankhel has been shown covered in flames at times but it doesn't seem like a flame armor. I am guessing rocks are simply good defensively rather than this being the default form of native powers.
It simply ranker/high ranker cannot attach the shinshu that they changing to some element like rak do, even the ruler last station, we didn't see he/she can attach his/her ice element to his/her body like rak do, or AA that he only can attach it to his weapon, rak can do both, attach the element to himself, and make spear from it, I think all of native one can do that for every element that they are control, they can attach the element to themself and make some imaginary weapon from it, they can throw it or wear it to make their attack more powerfull.
The case of yihwa I think is different from what rak do, she doesn't wear her fire, she is just on overwhelming condition that her fire coming out all over her body, same with evankhell IIRC that she cannot attach his fire to her body and make a imaginary weapon looks alike from that fire that attach to herself.