What is a jaspilite in geology ?

Jaspilite : definition

The jaspilites constitute powerful banded formations of siliceous and ferruginous sedimentary rocks, sometimes also manganiferous. They are formed by alternating beds of originally very fine silica (jaspers) which recrystallized under the effect of metamorphism, and ferruginous beds with dominant iron oxides (hematite and magnetite) with greenalite, chamosite and amphiboles, iron mineral accessories.

They are referred to by various names : ferruginous quartzite, taconite in the USA, itabirite in Brazil, and more generally under the term BIF (Banded Iron Formations). These jaspilites constitute the world's largest reserves of iron.