Affixes

The more general of the prefixes is ferro‑: ferroconcrete, concrete reinforced with steel; ferrocene, a crystalline compound containing iron between two flat layers of atoms; the adjective ferruginous describes a substance containing iron oxides or rust. The usual adjective is ferrous (but see below).

A few metals can be strongly and permanently magnetized; because this was first observed in iron, it is called ferromagnetism, though it is also shown by nickel and cobalt and their alloys.

In chemistry, ferro‑ refers specifically to iron compounds in which the iron is divalent, as in ferrocyanide, for which the adjective is ferrous; ferri‑ is used for chemical compounds that contain iron in its trivalent state, as in potassium ferricyanide, and here the adjective is ferric.