I don't know for certain, but I don't think that's stone at all...
...my gut feeling is that it's opalescent art glass - the type one would normally find in smaller pieces for use in stained glass projects.

Whatever it is, it's an absolutely stunning effect.

I think it may be a marble I saw a couple of years ago called "metro". Call a few marble yards asking about a strongly linear marble. Check out a quartzite called Luce di Luna as well, similar look.

It is a marble I believe sometimes called delano

It definitely looks like Equidae marble. It's available in honed and polished finished slabs. I saw a slab of this just recently at Pental Granite & Marble in Seattle. It's stunning! www.pentalonline.com

It looks like Meta Marble in Seattle has it as well. They call it "Mink" marble. http://metamarbleandgranite.com/

I have this installed in my Kitchen. It is from an area of Turkey called Marmarma. It has several names - one is Marmarma. Check out google earth - you will see huge quarry pits where Marmarma is located on the Earth. Marmarma is very hard for many to pronounce hence I think why they renamed it. also called Marmara Equador. I tink it is fine for a bathroom, but it chips too easily for a kitchen where pots/etc. hit the edge of the sink surround.

@ brendanem - i'm thinking of using it for my vanity. how are you liking it?

It is beautiful but it does chip very easily, I am super careful but my house keeper dropped a glass cup and it broke and nicked the stone, I have a great repair guy who polished it out but I say only light use and areas with out lots of edges!

I was going to use it exactly like you did - for my (very small) bathroom counter top. would you do it again?

and thank you so much for responding - such a bug decision :)