Mass in the asteroid belt

[pqloapq]

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?

[banner001]

...i would guess at number, as opposed to mass. If there are not massive mass differences between the different types of asteriod, one could asssume that 10% in numbers, was also 10% in mass...in anycase an educated guess is likely to be reasonable accurate given the wide diversity of asteroids.

[JulianO]

Well one way to think about it is what are iron asteroids?

They don't just appear ready formed, the basic asteroid is a a mixture of stuff left lying around from the formation of the solar system.

To get iron ones - you have to have differentiation. So they are normally formed by a biggish asteroid forming, and being hot enough that the constituents get hot enough to partially melt. In this case things like iron sink to the middle and lighter compounds rise to the top.

Then it somehow gets broken up, either by impact of ripped apart by a big bully like Jupiter, and the bits that were in the core are the iron ones.

So although it doesn't answer the question - there won't be more iron asteroids than there was iron in the asteroid belt, and then only those that have been subject to differentiation will distil into more solid iron asteroids.