Description
Ironstone is a sedimentary rock, either deposited directly as an iron-bearing sediment or formed by chemical replacement, containing a substantial amount of an iron ore compound from which iron (Fe) can be commercially smelted. Not to be confused with native or telluric iron, which is very rare and occurs in metallic form, the term ironstone is usually restricted to hard, coarsely banded, unbanded, and non-cherty sedimentary rocks of post-Precambrian age. The Precambrian deposits, which have a different origin, are generally known as banded iron formations. The iron-bearing minerals that form ironstones may include oxides, such as limonite, hematite, and magnetite; carbonates, such as siderite; silicates, such as chamosite; or a combination of these minerals.
