need help interior walls of a house built in 1943
I'm trying to do a little remodeling of a small room at my mothers house but I'm having trouble with the walls. I'll try to make my explaination as quick and easy to understand as possible... The house was built in either 1943 or 1948 and most of the house has standard drywall and it's easy to simply put a nail or screw in the wall in order to hang anything you can think of, but the room she needs done the walls and ceiling are made of something else. I'm in no way, shape, or form an expert so I have no idea what it is. All I do know for sure is:
1. It crumbles into powder and small chunks very easily
2. It's impossible to put any kind of nail or screw in due to the fact that no matter what type of nail/screw I use or how I try to put it in the wall simply crumbles away.
I've put a picture of a small piece roughly the size of a half dollar to hopefully show what I'm talking about a little better than I can explain. If anyone has any clue of what this is and any advice on the best way to hang shelves, or anything at all really I would greatly appreciate it. Thanks in advance!