In general, they are different from the dirt beneath our feet and the ores that we mine from our planet's crust. Likewise, they are much different than the Moon, Mars, etc. Asteroids are much more metal-rich, like the core of the Earth, Moon, Mars and any other planet. The asteroids are normally not as enriched in oxides, silicates, and the other lighterweight elements that floated up to dominate a planetary crust. Asteroids are more like a mixture of a planetary metal core plus a mantle and a crust.
Free metal is abundant in the mix, and often dominant.
This free metal can be used without any further industrial processing. The metal granules can easily be separated from the dirt using only magnets and soft grinders. Out come little metal disks, which are separated using simple magnets. The above is a very simple system to send to the asteroid. No advanced technology, so to speak.