Oh boy...this quartzite has had a lot of problems...search for "quartzite is staining". I'm so sorry.

It's the type of quartzite and if you search you'll find it's a continuing problem with the light colored quartzites. :(

"Installer claims they are mineral deposits in the stone."

The installer is lying. Those are not mineral deposits. Mineral deposits are randomly shaped and colored like, well, minerals. And even for this kind of quartzite which unfortunately is known for water staining, those spots are too regular a shape and pattern for that. Listen to the comment above by @Joseph Corlett, LLC. The source of those spots is squarely on the head of the installer, and it is a red flag that he is not owning up to it.

Edited to add: here is a pic of a quartzite with a lot of mineral spots and streaks. While it is a different kind of quartzite than yours, this pic is to illustrate the way minerals in quartzite look which is nothing at all like what you pictured.

Thank you so much for the clarity.

Not sure how this is going to play out if installer is lying. I’ll have to push harder.

Give the installer the benefit of the doubt. It's possible they just have no idea that something they did during the install could have caused this. I would let them know that after doing some research, you are convinced these are not natural stains or minerals. You can say that you've heard others experienced this due to glues or solvents used during install. Let them know you aren't happy with how it looks and ask them to make it right. But don't accuse them lying and turn it adversarial right away. However, do be adamant that it is not acceptable the way it currently looks.

@TT great advice thank you!

@T T that is great advice. You’re right, it’s not good to turn the conversation adversarial. That wouldn’t have a good result. I was mad on the OP’s behalf at the photos, because the contractor said the spots were mineral deposits. But being mad is not the right approach.

Unfortunately, verifying adhesive bleed means separating the stone from the substrate and seeing if the spots match.

Update…

Installer sent me a pic of the original slab and it has the spots on it! He questioned the supplier who told him it is mineral deposits. We are looking into our options because everyone who looks at our counters notices it and I’m not happy.

In that case, this falls on the supplier. Those are definitely not natural as it occurs in a pattern that looks like something dripped on it. However, your fabricator also has some responsibility. Didn't they look over the slab before cutting it up and fabricating? They should have noted those spots and perhaps put a pause on things to make sure that it was acceptable. Did you look at and pick those specific slabs in person?

I never had a chance to look at the slab in person. The installer is now saying he should have consulted with us before installing. Installer is talking to supplier in hopes of getting a different slab. What do you think would drip to cause those marks?

If you read the dozens of horror stories here on Houzz about quartzite staining, and often after installation, you will choose another counter material.

Hmmm that’s something I’ll inquire about. We’ve already paid for the quartzite so not sure the company will allow that.

"The installer is now saying he should have consulted with us before installing."

He is correct. Once a blade kisses a slab, the fabricator owns it. The supplier is off the hook.

If you read the dozens of horror stories here on Houzz about quartzite staining, and often after installation, you will choose another counter material.

Yes some quartzites stain but many others don't. Mine is perfect after 5 years.