Don't risk it! My fabricator used it to remove epoxy from my Caesarstone, on the advice of the Caesarstone sales rep, and it dulled the surface. Caesarstone wouldn't do a thing about it and they had to pay for a new slab. Quartz has a resin binder, and BKF is an abrasive.

NO, good chance BKF will etch or leave residue on the stone.

Get some plain steel wool--I think I usually use 000 (can also use 00, which is coarser, and 0000, which is finer--I use whatever I have handy. Try it out first on in an out of the way area). I buff away mineral deposits or errant marks that resist cleaning with alc-water spray and a microfiber cloth. It also buffs away rings (water deposit) from coffee cups or glasses.

I wouldn't use the kind that is like comet, but the kind that's like soft scrub should be ok. If it doesn't scratch/dull a stainless steel sink, could it really hurt a rock?

I don't know about the mineral deposits, but a VERY dilute solution of bleach and water will kill most everything. I found a link, they recommend 1/3 cup bleach per gallon of water for countertops. Honesty, the more dilute solution of 1 Tbsp/gallon would probably do the job and would be safe for most everything.

Here is a link that might be useful: Disinfecting for Norovirus

I have been on this forum too much when I read your subject line as "can you use beekeepers friend on granite?". I thought, what? She has marble! I have gotta get out some more!

Barkeepers friend is a stainless steel cleaner formulated with some fine abrasive and 5-10% oxalic acid.
Should be ok on granites as they are acid resistant and hard enough to take a very mild abrasive. Itshould do well removing mineral deposits near faucets. Always test first because some granites which are resined or dyed can be affected by acids.
I like to remove mineral or calcium buildup with a single edge razor blade(held at a 45 degree angle) and MB-3 or diluted vinegar(test first)
Always test new products in an out of the way spot or a sample piece just to be safe.
As far as disinfecting 1.5 oz of bleach in a quart of water sprayed on the area and left to dwell for 7 minutes should do the trick. Vinegar is also a good disinfectant as well on granite that you have tested it on.
I like 3% volume hydrogen peroxide-use it on your countertops and let it dwell for 7 minutes than wipe off.
Is a great disinfectant and is non-toxic to all.
Is 100 % biodegradeable as well. Regulated disinfectants are toxic.

The recommended bleach formula for labs is 1/2 to 1 cup of bleach to one gallon of water ... spray it on liberally, let it sit for 10 minutes and wipe it off.

That should not be strong enough to hurt granite.

But it will kill Hanta virus, HIV virus and many other nasties.

Thanks all. I was afraid to try the barkeeper's friend and I'm glad I didn't. My granite has been in about a month, and the rough spot is also a really dark place in the granite and may just be rough. I'll try steel wool or razor blade on it though.

I don't think the bleach solution I mixed was even that strong lazygardens. It was whatever the cdc recommended and I don't remember it now. Didn't hurt it though.