Try to avoid single pixels, especially in high contrast areas like a shadow and highlight right next to each other unless you want to make it sparkly.  When doing detail the form and implication is much more important than exactness.  Also, even though this is a side view you still should have a little of the top edge to give it depth.

I really like the craggy shapes you put into the stone.  My only worry is that it's too busy and will have to be toned town to match the already completed art.  I'm too lazy today to check.

I did an edit, feel free to build on it.

Nice work!

So what is the current status of the OPP? The wiki seems to be down, and the Pixeljoint forum hasn't seem much posts since early september it seems.