I can't see this resolving. Maybe they put them in and ordered another slab to be installed after? I imagine ANYONE would think this is acceptable - except to get a CO and then resolve.

(edited for first post making me look drunk)

There are many post on these forums (kitchen and building) with white-gray quartzites that have similar staining. You might want to do some searching. It usually doesn't have a great outcome.

What name did they give this "quartzite"?

Did you do any tests on the slabs?

It could be a dolomite or a marble?

Take aBernz-O-Matic to them please. You may watch it disappear.

Good lesson to inspect the counters before they leave the fabricators shop.

When your builder said "I know you’re in a rush to get your C.o.” he was basically saying "I'm in a rush to get my last payment and I'm putting the blame on you." I'd be extremely unhappy! That's a bigger stain area than what we typically see. Based on how your first picture shows that the stain stops at the seam, I think you're right that it's a fabrication issue and not glue or other moisture seeping in after install (as we've seen in other posts.)

However, I'm not a pro. Just chiming in to say that although you have to be out of your current place soon, I would try not to rush this. Even if you have to live with plywood counters for awhile, I think it's worth getting it right; that might mean switching stones and/or fabricator.

I'm so sorry this is happening to you!

That is much more likely to dry out in an air-conditioned home than it is on a rack is a humid fabricator's shop. Just because the builder and the schedule benefit doesn't mean it's the wrong decision.

I dont think you need kitchen counters in place to get a C.O. People move in with plywood kitchen counters all the time. The builder is hoping you don’t know that.

You have time to get the counter situation sorted. That is because, and reiterating the above comment, you don't need your final counters installed for the Certificate of Occupancy. You do however need a connected kitchen sink and faucet. That can be done with plywood counters and either your sink or an inexpensive laundry/utility sink. Your lack of stone counters will not prevent your Certificate of Occupancy.

Also reiterating what @chispa wrote. I am sorry to say that if this counter stained from water during fabrication, it is going to stain from water from daily use, especially around the sink. We have seen many stories about this. What you have is likely not quartzite, but rather marble. I would not blame the stoneyard though - most of the time, they have no idea, and sell how the stone name is told to them by the distributor.