Ironstone is a fine-grained, heavy and compact sedimentary rock. Its main components are the carbonate or oxide of iron, clay and/or sand. It can be thought as a concretionary form of siderite. Ironstone also contains clay, and sometimes calcite and quartz.
AppearanceFreshly cleaved ironstone is usually gray. The brown external appearance is due to oxidation of its surface. Ironstone, being a sedimentary rock is not always homogeneous, and can be found in a red and black banded form called tiger iron, sometimes used for jewelry purposes.
OccurrenceIronstone mostly occurs in the form of nodules, for example in seams in the coal measures.
Ironstone as a source of ironIronstone is a bountiful and widespread source of iron (Fe), although it only contains less than 50 percent iron, far less than the other main source of iron, hematite. Historically, most of British iron originated from ironstone, but it is now rarely used for this purpose.
ironstone in Dutch: IJzerzandsteen
ironstone in German: Eisenerz