Would they really breakup?
I know many small asteroids can break up while entering the Earth's atmosphere, but they are also traveling well in excess of 30,000+ mph when they hit it. I'm talking about a controlled drop from low Earth orbit. These blocks wouldn't be traveling faster than 17-18,000 mph. Plus, their angle of entry could be controlled so as to minimize the shock wave. If something as fragile as a space capsule can be safely deorbited then why not a large solid block of high grade iron-nickle ore?