Way is my rock turning white?

[Bob Escher]

It May be something simple but more than curious
I cam home today after a appt and noticed rock had turned completely white as if the spot had been knocked off the rock
It couldn’t have been and I noticed it elsewhere but didn’t think anything of it
Water parameters are fine

Thankd

 

[Big G]

My rock flakes off a chunk every now and then, and it is bright white. You could lift out a small piece of your seasoned rock and chip a bit off to see if it looks the same.

 

[Bob Escher]

But there’s not any residue on the sand unless it just crumpled into dust almost
Is that what happens