Origin of Asteroids

It's true that asteroids are pretty much void of quartz, and Brown handwaves this away by saying it melted away, but he apparently doesn't know much about asteroids/meteorites. Meteorites have a lot of volatile minerals, including things like clays, iron sulfide, and magnetite. These minerals all vaporize/change at temperatures much lower than 1300 F. Why aren't they all gone as well?

There's not too much introductory data online, because it's not really something too interesting to people who don't study meteorites. Essentially it goes something like this- troilite (FeS)forms via the gas-solid reaction of iron and hydrogen sulfide:
Fe + H2S --> FeS + H2
The thermodynamics of this equation are such that the reaction occurs at ~750 K (500 C). The reverse reaction (loss of sulfur gas) occurs a bit higher, around 900 K, due to some other thermodynamic factors, mainly eutectic melting. Analogous arguments can be made for clays and magnetite. All of the reaction temperatures are much lower than Brown's quartz melting.There are a lot of other problems with Brown's asteroid nonsense, and I'd think the site was a spoof too if the guy wasn't so serious.Here's a Science article by Brearley that provides a quick bit of info:
Just a moment...