One thing about sand it gets pushed around when interact with objects so depending on how much force applied it should create at least a really small crater around it/ some sand that pushed away on getting there.
Also the helmet got there somehow (probably rolled over there?) leaving marks. Otherwise if it been there for a while it might have some sand blown onto it.
The material depends on it should look watching tutorials on how to make materials is nice, one of the better cycles tutorials I’ve found is: https://www.youtube.com/watch?v=U4s3o21Owm0
Part two is where he starts creating materials but getting some terminology never hurts.
One thing that would help is to smoothing out the edges on the helmet, the sharp ones, now it looks as a halo 1 helmet which is nice but making the material, the edge might not look as expected.
Lastly the back of the helmet looks to dark as some light would bounce, adding a light with low emission lighting up the back helps but i’m unsure about the best way to properly fix it.