Ironstone is a sedimentary rock, either deposited directly as a ferruginous sediment or created by chemical replacement, that contains a substantial proportion of an iron ore compound from which iron (Fe) can be smelted commercially.
Not to be confused with native or telluric iron, which is very rare and found in metallic form, the term ironstone is customarily restricted to hard, coarsely banded, non-banded, and non- sedimentary rocks of Phanerozoic age. The Precambrian deposits, which have a different origin, are generally known as banded iron formations. The iron minerals comprising ironstones can consist either of oxides, i.e. limonite, hematite, and magnetite; carbonates, i.e. siderite; silicates, i.e. chamosite; or some combination of these minerals.[U.S. Bureau of Mines Staff (1996) Dictionary of Mining, Mineral, & Related Terms. Report SP-96-1, U.S. Department of Interior, U.S. Bureau of Mines, Washington, D.C.][Neuendorf, K. K. E., J. P. Mehl Jr., and J. A. Jackson, J. A., eds. (2005) Glossary of Geology (5th ed.). Alexandria, Virginia, American Geological Institute. 779 pp. ]
Description
Freshly cleaved ironstone is usually grey. 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 or opal gems.
Occurrence
Ironstone occurs in a variety of forms. The various forms of ironstone include siderite nodules; deeply weathered
saprolite, i.e. (
laterite); and
Oolite ironstone.
Uses
Ironstone as a source of iron
Ironstone, although widespread, is a limited source of iron. Historically, most British iron originated from ironstone, but it is now rarely used for this purpose because it is far too limited in quantity to be an economic source of iron ore.
Ceramics
Ironstone's oxide impurities render it useless as a component in
: the "
ironstone china" of Staffordshire and American manufacture, a fine, white, high-fired vitreous
semi-porcelain, commonly used for heavy-duty dinner services in the 19th century,
[G. Bernard Hughes, English and Scottish Earthenware, Abbey Library] includes no ironstone in its production. Its "iron" quality is in its resistance to chipping.
In construction
The stone can be used as a building material. Examples include the
at
Kirby Bellars and
South Croxton in
Leicestershire, and
Eydon Hall in
Northamptonshire.
In art
Sculptures carved out of ironstone are rare. One example is
Henry Moore's
Head created in 1930.
See also
