Materials
Why amorphous structure matters more than SiO2 content
A datasheet figure tells you what is in the bag. Structure tells you what it will do once it is in a formulation.
Silica is usually specified by one number: how much SiO2 a sample contains.
Structure decides reactivity
Amorphous silica has no long-range order. Its surface is available, and that availability is what chemistry can act on.