Is someone cleaning the counter by spraying cleaning products on the edge and onto the underside that is not protected?

No cleaning products used other than warm water and a dry towel

Someone else had that same problem, maybe a year ago or so? I can't remember the thread title though. The stone is called White Macaubus and searching that might help find it. Also, it's quartzite, not granite, but it's an awesome stone. I don't think the other person ever found a resolution or even a cause to this problem. Good luck - I hope you can figure it out!

Ci_lantro thanks for that link!

That appears to be, as the link above suggests, simply moisture in the stone. All natural stones are porous, and Macaubas is no exception. Use less water when cleaning perhaps. Potentially a cleaner rather than water. Method makes a stone safe cleaner that works well.

This is contamination from use. Get a poultice from a stone supplier and follow the instructions. May take several applications; good luck.

Yes, it's definitely not moisture as we've dried it for weeks - while away on vacation and it was still there. Will try the poultice for a supplier. Tried a homemade one and it wasn't as successful.

Yes this an oil stain to the granite, all white granites will show a grey stain from it. Joseph has advised how to remove.

Though you will need to seal the stone to stop it coming back.