Granite generally doesn't etch and dark granites like absolute black, blue pearl, uba tuba, etc. generally don't stain and don't need to be sealed. By the way some stone that is sold as commercial granite is technically not geological granite - blue pearl isn't - but they're perfectly nice countertop stones. Sounds like your sample may not really be absolute black - there's lots of inferior stones being passed off on unsuspecting consumers.

Try a second test- rub the counter with a clean white cloth that has acetone on it. If any black comes off, your granite has been dyed to make it appear blacker than it really is. Acetone is uesd to clean granite after install to remove any residue and will not harm the surface. It will remove dye though. I would definitely show the sample to your granite supplier and ask questions. I wouldn't accept the slab your sample came from.

Thanks for the info. I will try the acetone as well on any future samples. The stone yard actually gave me a sample of their AB "tile" as opposed to a piece of slab. I had assumed it is the same material, but maybe not.

From what you both said, may I infer that actual/real AB is a granite, and should not etch, and therefore if a stone is marketed as AB and does etch it is something else? Or is AB one of those stones that varies in its calcium content (perhaps depending on conditions where and when it formed, etc.), and so some AB would etch and some would not? (I've heard that is the case for some of the quartz stones--that they vary in hardness and composition depending on where they came from). Or does AB vary in color, and so they treat the lighter variations with a "topcoat" of some sort, and that is what is etching?

I don't know enough about granite to comment on the composition of the stone. I don't think any AB should etch. But if you had a sample that was treated with dye, your lemon test may have begun taking the dye out, as acetone would. Also, I don't think it's a matter of some AB needing a topcoat. If it's been dyes to make it appear blacker, you are paying for AB when you may be getting a cheaper or less desirable stone. It may be perfectly fine for a countertop, but your not getting what you pay for and it will fade.