From wiki: materials science
"The major determinants of the structure of a material and thus of its properties are its constituent chemical elements and the way in which it has been processed into its final form."
This is why the folks who insist on mass composition above all else are missing the point. The structure of the atoms determines the property of a material as much as the elements that a material is made of.
If you have a foam-like object and determine that it is made up largely of iron, and this has been found in the WTC dust, wow! So it being iron ain't enough. It has to be iron foam, and it has to be found in the WTC dust to show that a plane crash did not destroy the WTC. Unless plane crashes generate metallic foam, which they don't.