VOlga Blue Granite

I found 2 beautiful slabs ov Volga Blue.  I'm told that thge slabs were really inique because they are more black and loaded with lrge chips of "Mica" and blue reflections.: they also don't have musch of the green in them.  My installer started the install and I found a black line from the front left to the back right in one of the pieces. When asked about it he said that it was a "vein" and typical in Granite.  When I did my pre-cut inspection I looked very carefully over the pieces and ran my hand over every in and I found no "veins." 

Are veins "typical" adn would they be a dark black line that goes all they way throught the slab in Volg Blue?

Charles