Alloy of iron and manganese used in basic and acid open hearth steelmaking practice A high manganese pig iron containing 15-30% manganese and used in bessemer and open-hearth steel production. See Pig Iron.

Spiegeleisen (German: Spiegel— mirror or specular; Eisen—iron) is a ferromanganese alloy containing approximately 15% manganese and small quantities of carbon and silicon. Historically, this was the standard form in which manganese was traded and used in steel making (see Bessemer process); today, manganese is usually traded and used in more concentrated form, 80% manganese content being typical.