A few days ago, we noticed a blue stain in our bathroom countertop just next to the sink. Please see the attached photo. For scale, one arm of the L-shaped stain is just under half an inch.
The stain appears to be under the surface of the marble. It does not come out with our regular stone cleaner (Rock Doctor Granite).
We're thinking it might be a cleaning product of some sort. Our housekeeper was over right before we noticed. The colours are off in the photo; it's a much lighter blue than you see. The blue cleaning products we use are: Windex and Toilet Duck. I imagine the Toilet Duck is pretty acidic, but there is no etching at all. The countertop above the stains is very smooth.
What could cause these stains so quickly? In any case, is there any way I can draw the stains out of the marble? Would the baking soda paste trick work like it does for oil stains in granite?