It looks like a vein-cut calacatta marble. When it's vein cut, you can see the horizontal lines like in the photo shown.

Thank you!

How do you deal with a seam with a striated countertop like this? I love this stone, but don't know how seams would look.

We typically try to bookmatch slabs (so that two adjoining surfaces mirror each other in appearance, thus giving the impression of an opened book). This will reduce the appearance of a seam in the countertop.

I've been looking everywhere for a countertop like this made of quartz. What is the brand? Is "Quartzite" the brand? I saw in a different post that it is "white" quartzite. Any more specifics would be greatly appreciated! Thanks.

It is a natural material known as 'white quartzite.' We have found it to be hit or miss as far as vendors carrying it. What was an unusual find, seems to be rising in popularity - as more vendors have expressed interest in supplying it. In the Cincinnati area, Mees Distributors has been our local source.