If you run your finger over the spot, does it feel differently than the rest of the slab?

Also, did the installer call your attention to it? He should have. Buying quartz is different than going to a yard to see a granite slab before you purchase it. Quartz, you find a sample you like and expect the entire piece to look the same. Because it is ground stone, I guess it is possible to have one spot like that...but, I agree, that would drive me nuts.

I could see settling for a flaw if it was real stone, but quartz should be consistent throughout.

I have seen variations in slabs of quartz. They are not identical and not always consistent.

looks like a piece of something else fell into the cookie sheet before it was baked.....i'm thinking you didnt have to ok your slabs before installation, they made me look at my quartz before it went in.