Identification needed for white encrusting stuff

[catshanon]

I had put in some dead base rock with some wet sand in my 60G tank 2 weeks ago. The rock used to wick up the water in the salt as I could see the rocks turning a shade of purple where the old coraline algae used to be.
Today I saw a white encrusting crystal like growth over some of the rocks,..Is this some kind of salt creep, or what is it ? The tank is sitting dry right now.
Any help will be appreciated ?
Thanks,
Raj

[hillegom]

I assume this is a porus rock. And it is above water,
So if it has water in the pores and is drying out, then the water evaporates and the salt crystalizes out.
I am sure if you put the rock in the water again, the salt crystals will dissolve.