Is it meant to be like a hard rock, or a crystal? Cause right now, I read it as soft, a bit jelly-like. I thought more harsh straight lines would give it a harder appearance, so I fiddled around with it thusly:

I shifted the colours to go bluer when darker, added more highlights, used more angular shapes, did some pixel-level refinements, but there are some irregularities left (like that curved bottom-right). But those 90 degree angles in the shading are deliberate. A bit experimental. Like em?
I think I inadvertently made the face area look kinda flat in comparison to the depth that the upper shading gives...
ETA: I just found that this is a pre-existing character:
http://jontronshow.wikia.com/wiki/Rockington