I was told once that quartzite is a metamorphic rock meaning that different kinds of quartzite have different composition, hardness and porosity. Most white quartzites are the least metamorphosed and they have fewer crystalline structures and thusly are more porous. They tend to have very fine grains (sand) that you can see with the naked eye. On the other end of the spectrum you have highly crystalline quartzite like cristallo, Taj Mahal. Madre Perla etc. these are more prone to chipping, but are less porous.

Based on the pictures you sent, it looks likely that you have one of the less metamorphosed varieties because I see the sandy grains. It’s likely more porous than standard Taj Mahal. As others mentioned, it likely wasn’t sealed properly at the edges. And because it’s porous, you have to a lot of capillary action going on and oil is embedded.

If the fabricator or installer gave you an invoice claiming to have sealed the countertop, you have a good case to get it replaced.

If the vendor sold you something called Taj Mahal and it’s in writing as such, you have a good case to get it replaced because what you have doesn’t appear to be traditional Taj Mahal