Ironstone

From Wikipedia, the free encyclopedia

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.

Contents 1 Appearance 2 Occurrence 3 Ironstone as a source of iron 4 See also

[edit] Appearance

Freshly 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.

Sometimes ironstone hosts concretions or opal gems.

[edit] Occurrence

Ironstone mostly occurs in the form of nodules. It is easy to find ironstone overlying coal measures.

[edit] Ironstone as a source of iron

Ironstone is a bountiful and widespread source of iron (Fe), although it only contains <50% 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.

[edit] See also

• Iron ore
• Banded iron formation