This painting really impressed me. Even tho it's just a practice i can't help but love the way you rendered it.
Awesome knowledge of values, the shapes are well defined and you can almost feel the roughness of the stone thanks to the light noise. All the proportions look good to me, maybe the original head is a little longer vertically, but not much of an issue.
The hair are astonishing, the details are very well done.
The only little thing I can complain about it's that some edges are way too strong that they should be: e.g the inside of the ear, the countour of the eyelids (I know there should be a stronger shade, but still, it's a little too dark in value)