Bog iron

Iron-bearing groundwater typically emerges as a spring and the iron in it forms ferric hydroxide upon encountering the oxidizing environment of the surface.

[1] This affinity combined with the porous structure and high specific surface area of bog iron make it a good natural sorbent.

[2] These properties combined with the fact that bog iron is cheap to obtain are incentives for its utilization in environmental protection technologies.

Iron made from bog ore will often contain residual silicates, which can form a glassy coating that imparts some resistance to rusting.Iron is carried to bogs in low-pH, low-dissolved oxygen iron-bearing groundwater that reaches the surface through springs, along with structures of fractures, or where groundwater intersects surface flows.

[4] Factors such as local geology, parent rock mineralogy, ground-water composition, and geochemically active microbes and plants influence the formation, growth, and persistence of iron bogs.

[8] Smelting with a bloomery furnace often results in between 10 and 20 mass percent Fe being reduced to iron bloom, while the rest is transferred into the slag.

There is some archaeological evidence that lime was added to furnaces to treat silica-rich ores that were difficult to smelt by the bloomery process.

Iron production sites in central Sweden are dated to the late Bronze Age and the innovation might have been transmitted from both the south and the east.

There is evidence of a direct relationship between Viking settlements in northern Europe and North America and bog iron deposits.

[5] This supports the idea that iron processing knowledge was widespread and not restricted to major centers of trade and commerce.

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.

[18] In Central and Southern New Jersey, bog ore was mined and refined for the production of naturally rust-resistant tools and wrought iron rails, many of which still grace staircases in Trenton and Camden.

The remains of a commercial smelting operation near Snow Hill, Maryland, are now a state and national historic site.