Bog iron
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Bog iron refers to impure iron deposits that develop in bogs or swamps by the chemical or biochemical oxidation of iron carried in the solutions. In general, bog ores consist primarily of iron oxyhydroxides, commonly goethite (FeO(OH)). It was discovered during the Pre-Roman Iron Age, and most Viking era iron was smelted from bog iron.
Iron-bearing groundwater typically emerges as a spring. The iron is oxidized to ferric hydroxide upon encountering the oxic environment of the surface. Bog ore often combines goethite, magnetite and vugs or stained quartz. Oxidation may occur through enzyme catalysis by iron bacteria. It is not clear whether the magnetite precipitates upon first contact with oxygen, then oxidizes to ferric compounds, or whether the ferric compounds are reduced when exposed to anoxic conditions upon burial beneath the sediment surface and reoxidized upon exhumation at the surface.
Iron made from bog ore will often contain residual silicates, which can form a glassy coating that grants some resistance to rusting.
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[edit] Colonial America
Bog iron was widely sought in colonial America. Lake Massapoag in Massachusetts was drawn down by deepening the outlet channel in a search for bog iron.[1] The Saugus Iron Works National Historic Site, on the Saugus River in Saugus, Massachusetts operated between 1646 and 1668. The site contains a museum and several reconstructed buildings.[2] The success of the Saugus Iron Works, and the rapid depletion of the region's natural bog iron, led them to send prospectors out into the surrounding countryside. In 1658 they bought 1,600 acres (6.5 km2) of land which covered areas that are now Concord, Acton, and Sudbury. They set up a large production facility in Concord, Massachusetts along the Assabet River with dams, ponds, watercourses and hearths, but by 1694 the natural bog iron there had also been exhausted, and the land was sold for farming.[3]
The John Winthrop, Jr. Iron Furnace Site, on the National Register of Historic Places in Quincy, Massachusetts predated the Saugus site by a year, but on a smaller scale and with less success. Put into operation in 1645, it is considered to be the oldest iron blast furnace in the United States, although it operated for only two years.
In New Jersey, bog ore was mined and refined in Central & Southern New Jersey for the production of tools and wrought iron rails (many of which still grace stairs in Trenton and Camden), which took advantage of its natural rust resistance. During the American Revolution, the iron was used for cannon balls for the American colonial forces.
Bog iron was also found on the Eastern Shore of Maryland. The remains of a commercial smelting operation near Snow Hill, Maryland are now a state and national historic site. Known as Furnace Town, it was called the Nassawango Iron Furnace after the nearby creek. The commercial furnace ran from about 1825 to 1850.
[edit] See also
- Limonite
- Iron ore
- Ore genesis
- Acidithiobacillus ferrooxidans (iron oxidizing bacteria)
- History of ferrous metallurgy
[edit] References
- ^ Diana Muir, Reflections in Bullough's Pond, University Press of New England, 2000.
- ^ http://www.nps.gov/sair/index.htm Saugus Iron Works
- ^ http://www.concordma.com/magazine/maraprmay02/ironworks.html The Concord Iron Works
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[edit] External links
- Hurstwic: Iron Production in the Norse Era
- Talzhemir's Bog Iron Page
- Bog Iron Industry in The Pinelands, New Jersey
- ironfurnaces.com - a free wiki dedicated to the preservation of iron furnaces
- Bog Iron Formation in the Nassawango Watershed, Maryland U.S. Geological Survey: Open-File Report 03-346
- American Society of Mechanical Engineers, Nassawango Furnace landmark.
- ASME PDF file with detailed reconstruction drawings of the furnace and surroundings.
- Nassawango Furnace at the Maryland Historic Trust.
- “A Brief History of Nassawango Iron”
- Furnace Town, Snow Hill, Worcester County Maryland.
