What is this white crystal like substance?

We bought a fifty year old house about 3 years ago. Over the weekend while cleaning the basement, I noticed this in a corner. There is an unfinished, unheated concrete room on the other side of the wall that is right beneath our front porch. I’m wondering if maybe that room is causing moisture? But back to the photos…any clue on what that is? It’s sort of powdery and crystalline. Do I need a mold specialist or can I clean it and put a fan on it to dry out any residual moisture?