I seal everything because I have this “ounce of prevention is worth a pound of cure” mentality. I would go ahead and seal with a high quality impregnating sealer. I’m using Dry treat Meta Creme on my Cygnus Quartzite. It’s super easy to apply and water clean up with no nasty smell. Seems to be doing a very nice job.

***however I’m no expert, just a crazy homeowner***

Applying sealer does not enable stone to etch. I'd try some high quality sealers on scrap first.

^^^ definitely test on scrap!! I tested on 3 different pieces of scrap allowing the sealer to sit for different lengths of time before touching my actual counters

Regarding the Absolute Black granite, the answer is do not seal. I repeat, do not. Different granites have different densities or "absorption rates". If a stone has a high absorption rate, that means it absorbs things readily, and needs to be sealed to prevent that absorption of things you might spill that would stain. However, Absolute Black is the most dense granite there is, with an extremely low absorption rate. That means that if you apply sealer, the stone is too dense to absorb it. The sealer would just sit on the surface of the stone. That leads to hazing, which is a cloudy haze appearance on the stone from sealer not being absorbed. The haze can only be removed by removing the sealer with acetone. As I said, do not apply sealer to Absolute Black.

BTW, Absolute Black isn't the only granite that doesn't need sealer. There are quite a few different granites that are dense. My granite counters are 12 years old, have never been sealed, and look like the day they were installed.

Unfortunately there are a lot of bad counter fabricators who have not bothered to learn which granites need to be sealed and which don't. They just apply sealer to everything. Absolute Black's appearance would be marred by sealer.

Regarding your comment about etching - AB won't etch. If a stone is going to etch, like marble does for example, no sealer will stop that. Sealer is to prevent stains, not etching.

Regarding your quartzite, I don't know if it needs sealer or not. There have been a number of threads on this forum that talk about it, and you should look for those.

Kiki RyanBoth will need to be sealed especially any white natural stone

Drytreat 40sk for the AB and either that or metacreme for the quartzite. The above information about AB the water absorption rate is still high. Yes you do not have to seal polished AB as polishing closes the pores of the stone off... but matte is different the pores remain slightly open, hence it does not have the light reflectivity.

We would suggest sealing the black, but not with a film sealer and with only something that like the above.

People who manufacture / sell sealer always advise sealing. This ranks right up with 'snake oil'.

Put several drops of water on the counter - wait 10-15 minutes. If it isn't absorbed, it doesn't need sealing.

We had Zodiaq quartzite (now Corian Quartz) for seven years. Never waxed, never sealed. Never changed. Corian says no wax or sealers necessary.

Check with your quartzite manufacturer. (Unless you believe their strategy is to have their product deteriorate in a few years, so you'll buy new counters from them.)