Actually, black powder is still used in quarrying, especially for gravestones, countertops and other applications where you don't want the microscopic cracks that can be caused by higher speed "fracturing" explosives such a nitroglycerin, dynamite, tetral, TNT, and stuff like them there. I've never heard of slurry (ANFO) being used in quarrying, but I suppose as a heaving explosive it could be -- I don't know about the cracks it would leave in the rock, though. I knew one old quarryman who swore that the best rock came when holes were drilled, filled with water, and the rock allowed to crack off when the water froze.

Black powder contains potassium (or sodium) nitrate, sulfur, and charcoal. See a good public library for the proportions.

I'm not involved in explosives anymore; I run a public library. It's just one of the things I've done in the past.

By the way, the AP is reporting that the bomb was moved because the officers thought it was a hoax.