The piece you pictured is very nice, and beauty is in the eye of the beholder. That said,
better lapis has no visible calcite (white) in it. It may or may not have flecks of gold
(pyrite) in it... I believe some people like the gold flecks and some don't...I myself
like it. The deeper and more ultramarine the blue is, the better the grade of lapis.
Lapis is often dyed to deepen the blue, but usually you can see the dye in veins
in the structure and acetone or alcohol will make it come off on a rag.
I have an interesting slab of lapis here that I bought last summer. It is half blue and
the other half has white in it, but if you turn it over, the white half is pure blue on the
other side. I think that as long as it is face up deep blue, the white doesn't devalue it.
If I find out that's not so, I'll just put it in a closed bezel, so you can't see the calcite.
Anyway, I think I'll try to get some more from the guy who had this slab at the July show
in Franklin, NC. I think I can sell the cabs...