Try dripping a few droplets of water in the same area. If the water beads up (i.e., doesn't absorb into the stone and leave dark/shadowy spots), it's likely the ring is an oil stain -- which means your contractor likely didn't use a sealer that protects against both water- and oil-based liquids. Any idea what brand he used? Also, what type quartzite do you have? Close-up looks similar to my Calacatta Gold.

A sealer does not prevent staining at all, it just slows the absorbtion, it will still stain if left to sit on the surface long enough. You need to use a pultice to attempt removal.

did you ever get the stain out? I had a very similar problem, and from a picture I took while the fabricator was sealing in the home, it looked like it was the round bottom of the sealant that had to do with the ring. As I had not used the counter, and have a photo of his sealer on the exact spot (could tell by markings of the quartzite!)

very frustrating!

Just found this post - we also have a similar stain on the exact same stone and am trying figure out how to remove it. Wondering if you had success with anything specific?

That looks like a vacuum pod mark to me. Measure the diameter then go to your fabricator's shop and measure the vac pods on his CNC machine and/or his lifters or those of his supplier.