Congratulations, not mold! I think everyone goes thru that phase, worrying about damp and wood and basements etc. Mold won't grow on stones - it likes wood, however.
It IS probably from dampness, tho that is usually not a problem. That appears to be a mineral leachate coming from the stone, called 'efflouresence'. I have some in my basement; the stones are sulfur-containing, the leachate is yellow, and is actually sulfur! You can smell it if you put some on your finger.
I wouldn't worry too much about it other than maybe taking a wire brush to it and then shop-vacc'ing the dust up. Do that every 10 yrs
The other thing I've seen done is that ppl will parge the basement walls with mortar/lime, 2 coats, and give the 2nd coat a brush finish. But that is entirely non-restorational, although many people like it.
Are those dehumidifier knobs in the pic? Very good
Yes, more pics, please! ha ha