I ordered 75 pounds of fiji shaped marco rocks. The stuff is very porous and ranging in different sizes. I had a really huge piece (2 actually) that took up maybe 1.5 feet long and a good height too. For those, just take a hammer and screwdriver and chizel it. Those 2 came in the 50 pound box though. The smaller box had smaller rocks. Very light weight and porous. I guess 75 pounds was more like 125 pounds wet someone told me. I tried getting 75 pounds to go with my 50 pounds of LR from the old tank when I transfered tanks, but forgot about water weight, so I'm over 125 pounds for a 125 tank, which is ok. The thing is they have good surface area.
When you get them, they will probably be a bit dusty. Soak them in water and maybe scrub them a bit if you could, all I did was soak them.