Your shaders blow my mind.
I've personally been doing a material study of obsidian that I've been chronicling in my own polybook (http://community.cgcookie.com/t/polybook-grifter/8313/6). Your obsidian looks good and is probably more accurate than mine, but I feel like it's missing something. Obsidian is a highly reflective glass-like material that seems to me to have subsurface scattering properties, especially when it is smooth polished. It seems like most of the surface of your example is smooth enough that it ought to be reflecting recognizable images of the rock around it.