I have used it, not as 'mulch' per say but as a way to supress weeds. I've put down weed fabric (in this case black plastic painters would use) and covered it in crushed limestone, poke holes in the plastic, when it rains the water filters down to the roots and over time supplied a nice dose of lime to my otherwise sour michigan blow sand.
It was like $5's where i live to get the back of my truck filled w/ crushed limestone.