Several different things to address in your post:

- regardless of whether your stone is quartzite, granite or marble, sealing it should not cost $500. Most fabricators seal stone counters upon installation as part of the service, at no additional cost. If you want to seal your own counters, just go to Home Depot and buy 511 Sealer for about $20 for the smallest bottle (it will still outlast you in the home, since very little is used in each application). Follow the directions on the label, but basically if you are able to wipe on thinly, you can do it.

- “but will not warranty the quartzite against stains because they say the quartzite is so dense it doesn't thoroughly absorb the sealant.” Complete opposite things being said in one sentence. I don't know if they are blowing smoke, or if you just misunderstood them. When a stone is very dense, i.e. non-porous, it will not absorb liquids and it will not stain. Consequently, a dense stone does not need sealant at all. Furthermore, if you seal such a dense stone, the sealant will not absorb, and just sit on top, marring the stone’s appearance with haze and streaks. I suspect the company meant that due to the stone’s density, they will not warranty the stone against the hazing and streaks that could occur if it is sealed.

- if a quartzite is indeed a dense quartzite it should not be sealed for the reasons I mentioned above. What I do not know is whether your Aria Calacatta Quartzite is a dense quartzite. Different quartzites have different densities, just like different granites do. The quartzites that are more dense (Taj Mahal is a well-known one in that category) should not be sealed, and the less dense quatzites should be sealed. An easy test is to drip some water on your counter. Wait 15-20 minutes. If the water is still beaded on top, you don’t need to seal your stone. If the water has absorbed, the stone is porous and should be sealed.

You need a different installer and source.

I'd be extremely concerned integrity of these folks, and add

Has your LASER template been done?

Do you know how your veining will look

Do you have seams and do you know their location?

Have you thoroughly inspected the slab

Were you home for the template, advised on all above?

Were you asked to sign based on all above?

It is this???

You need to personally test this stone for porosity before anything is cut. And make sure it's really quartzite too.

Is there a way to test it for porosity in the showroom? They haven‘t cut any yet so there aren’t any samples.

"I'd be extremely concerned integrity of these folks"

@JAN MOYER - if indeed the OP's stone is dense, the fabricator is exactly right that it should not be sealed. If they are warning the OP that when sealer is applied to a dense stone it will mar the appearance of the counter, they are also exactly right. Usually we see on this forum the dumb fabricators who seal every counter, even stones like Absolute Black, and then the homeowner posts on here about the streaks and haze. So I do not agree with your comment about the integrity of the company. It seems to me that there are misunderstandings on the OP's part about how sealant works with different stones.

The real question is what @Joseph Corlett, LLC said - the crux is that the quartzite needs to be tested for porosity, as I also mentioned above. Then it can be determined whether the fabricator is correct or not.

"Has your LASER template been done?"

I've had several different kitchens in which templating was done old-school, not by laser. The fabricators often say that laser templating can be more troublesome than the stick templating that is the way it's been done for decades. And, whether laser templating or not, it's all about the expertise of the fabricator, regardless. I would never advise anyone that their fabricator must have laser templating rather than stick templating to be a good fabricator. That is not true.