I'm trying to find how much iron (by mass) is in the main asteroid belt. I'm finding a lot of sites that say 10% of the asteroids are M class, but is that by number or by mass? Does anyone know, and can you provide a reference?
Population demographics of the asteroid belt
1] class M [metallic] 10%
2] class S [stony] 15%
3] class C [carbonaceous] 75%
These are by count and predominant spectral characteristics. The relative mass composition is not well known for obvious reasons. The aggregate iron content is probably about the same as that of mars crust [estimated around 5%].