A matrix is the principal substance (usually more than 50%) in which a constituent is embedded. For example, when a plain carbon steel with 0.20% carbon is cooled very slowly from the molten state to room temperature, platelets or lamellae of ferrite and iron carbide are alternately formed. This microstructure is called pearlite, and it forms a constituent in an alpha- iron or ferrite base that is called the matrix. The pearlite is said to be embedded in a ferrite matrix.