Hierarchy classification:

1. top of the aat hierarchies
2. Physical Attributes Facet
3. Conditions and Effects (hierarchy name)
4. [conditions and effects by specific type]
5. [conditions and effects for metals]

Anotations

Scope note:

A reddish powder composed of iron oxide and hydrated iron oxide that forms on the surface of iron and iron alloys. Rust is formed by the oxidation of iron in the presence of moisture. At least 40% humidity is required for the corrosion to occur.