What is bog iron?
By Chelsie Vandaveer
November 26, 2002
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The sheets of ice that alternately covered and retreated during the Pleistocene left behind a landscape ground flat by the great weight of frozen water sometimes more than a mile thick (1600 meters). At the terminus or leading edge, the glaciers melted and deposited the loads of mineral dust and rock, moraines. The moraines often trapped the remaining meltwater; wetlands and slow moving streams formed within the flattened landscape. Sphagnum mosses pioneered the revegetation of these wetlands. Millennia of Sphagnum growth built peat soils.
Bogs are areas of wet peat-based soils. If dominated by grasses and sedges, they are properly called marshes; dominated by trees and shrubs, they are swamps. The anaerobic (low oxygen), acidic conditions of the soil provide habitat for the odd iron bacteria--Gallionella and Leptothrix species.
As iron oxide-rich waters seep or flow into marshes and swamps, iron bacteria precipitate the molecules into filaments or coatings which perhaps serve to protect the bacteria. Colonies of bacteria form nodules of iron ores, siderite or limonite. The ore nodules form within the peat soils, hence the name bog iron. The nodules vary in size with the length of time they had to form.
Bog iron is thought the first iron ore mined by humans. The practice may date as far back as 2000 BCE in Europe. Bog mines are the only mines with a renewable resource. The bog iron mining damages wetland habitats, but as long as the peat soils are left and water continues to enter the wetland, the ores replenish. Depending upon the amount of iron-oxide the water carries and its rate of flow into the wetland, new nodules of ore are ready for mining about every 30 years.
The Hurstwic Historical Society of New England has a fascinating page about how Vikings mined and used bog iron including photographs of smelted iron and implements. To view the page, click on the link:
http://www.hurstwic.org/history/articles/manufacturing/text/bog_iron.htm
The Monmouth County Vocational School District has posted a great article on the formation of bog iron. To learn more about how these ores are produced, click on the link:
http://www.mcvsd.org/mccs/geo-hths/bogiron.htm
Series: | 1 | | 2 | | 3 |
killerPlants Tendrils: ~~1~~2~~3~~4~~5~~
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