Bog iron is a form of impure
iron
Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...
deposit that develops in
bog
A bog or bogland is a wetland that accumulates peat as a deposit of dead plant materials often mosses, typically sphagnum moss. It is one of the four main types of wetlands. Other names for bogs include mire, mosses, quagmire, and musk ...
s or
swamp
A swamp is a forested wetland.Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p. Swamps are considered to be transition zones because both land and water play a role in ...
s by the
chemical
A chemical substance is a unique form of matter with constant chemical composition and characteristic properties. Chemical substances may take the form of a single element or chemical compounds. If two or more chemical substances can be combin ...
or
biochemical
Biochemistry, or biological chemistry, is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and biology, biochemistry may be divided into three fields: structural biology, enzymology, ...
oxidation
Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is ...
of iron carried in solution. In general, bog ores consist primarily of iron
oxyhydroxides, commonly
goethite
Goethite (, ) is a mineral of the diaspore group, consisting of iron(III) oxide-hydroxide, specifically the α- polymorph. It is found in soil and other low-temperature environments such as sediment. Goethite has been well known since ancient t ...
(FeO(OH)).
Iron-bearing groundwater typically emerges as a
spring and the iron in it forms
ferric hydroxide upon encountering the oxidizing environment of the surface. Bog ore often combines
goethite
Goethite (, ) is a mineral of the diaspore group, consisting of iron(III) oxide-hydroxide, specifically the α- polymorph. It is found in soil and other low-temperature environments such as sediment. Goethite has been well known since ancient t ...
and
magnetite
Magnetite is a mineral and one of the main iron ores, with the chemical formula . It is one of the iron oxide, oxides of iron, and is ferrimagnetism, ferrimagnetic; it is attracted to a magnet and can be magnetization, magnetized to become a ...
, and may include
vugs and stained
quartz
Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The Atom, atoms are linked in a continuous framework of SiO4 silicon–oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tet ...
. Oxidation may occur through
enzyme catalysis by
iron bacteria. It is not clear whether the magnetite precipitates upon the 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.
Bog iron, like other
hydrous iron oxides, has a specific affinity for
heavy metals. This affinity combined with the
porous structure and high
specific surface area
Specific surface area (SSA) is a property of solids defined as the total surface area (SA) of a material per unit mass, (with units of m2/kg or m2/g). Alternatively, it may be defined as SA per solid or bulk volume (units of m2/m3 or m−1).
I ...
of bog iron make it a good natural
sorbent.
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
silicate
A silicate is any member of a family of polyatomic anions consisting of silicon and oxygen, usually with the general formula , where . The family includes orthosilicate (), metasilicate (), and pyrosilicate (, ). The name is also used ...
s, which can form a glassy coating that imparts some resistance to
rust
Rust is an iron oxide, a usually reddish-brown oxide formed by the reaction of iron and oxygen in the catalytic presence of water or air moisture. Rust consists of hydrous iron(III) oxides (Fe2O3·nH2O) and iron(III) oxide-hydroxide (FeO(OH) ...
ing.
Formation
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.
The iron in the water is then
oxidized
Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is ...
by dissolved oxygen or, through
enzyme catalysis by
iron bacteria (e.g., ''
Thiobacillus ferrooxidans'' and ''
Thiobacillus thiooxidans'') that concentrate the iron as part of their life processes.
Presence of these bacteria can be detected by the oily film they leave on the surface of the water.
This change of oxidation state causes the precipitation of fine-grained iron solids near the point of groundwater discharge.
A variety of iron minerals, such as
goethite
Goethite (, ) is a mineral of the diaspore group, consisting of iron(III) oxide-hydroxide, specifically the α- polymorph. It is found in soil and other low-temperature environments such as sediment. Goethite has been well known since ancient t ...
,
magnetite
Magnetite is a mineral and one of the main iron ores, with the chemical formula . It is one of the iron oxide, oxides of iron, and is ferrimagnetism, ferrimagnetic; it is attracted to a magnet and can be magnetization, magnetized to become a ...
,
hematite
Hematite (), also spelled as haematite, is a common iron oxide compound with the formula, Fe2O3 and is widely found in rocks and soils. Hematite crystals belong to the rhombohedral lattice system which is designated the alpha polymorph of . ...
,
schwertmannite, and amorphous iron-aluminum-sulfate-rich solids, can be formed via oxidation of ferrous iron under the acidic conditions present.
All
photosynthesizers play dual roles as oxygen producers, and thus passive iron oxidizers, and as surfaces to which the iron can sorb or bind.
This causes aquatic plants to become heavily encrusted with a light-orange
floc of
iron oxyhydroxide near the point of oxygen gas released from the plants.
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.
Bog iron is a renewable resource; the same bog can be harvested about once each generation.
Iron extraction
Europeans developed iron
smelting
Smelting is a process of applying heat and a chemical reducing agent to an ore to extract a desired base metal product. It is a form of extractive metallurgy that is used to obtain many metals such as iron-making, iron, copper extraction, copper ...
from bog iron during the
Pre-Roman Iron Age of the 5th/4th–1st centuries BCE, and most iron of the
Viking Age
The Viking Age (about ) was the period during the Middle Ages when Norsemen known as Vikings undertook large-scale raiding, colonising, conquest, and trading throughout Europe and reached North America. The Viking Age applies not only to their ...
(late first millennium CE) was
smelted from bog iron.
Humans can process bog iron with limited technology, since it does not have to be molten to remove many impurities.
Due to its easy accessibility and reducibility, bog iron was commonly used for early iron production. Early
metallurgists identified bog-iron deposits by indicators such as withered grass, a wet environment, hygrophilous grass-dominated vegetation, and reddish-brown solutions or depositions in nearby waters.
They stabbed wooden or metal sticks into the ground to detect larger ore-deposits,
and cut and pulled back layers of peat in the bog using turf knives to extract smaller, pea-sized nodules of bog iron.
Early iron-production from bog ore mostly occurred in
bloomery
A bloomery is a type of metallurgical furnace once used widely for smelting iron from its iron oxides, oxides. The bloomery was the earliest form of smelter capable of smelting iron. Bloomeries produce a porous mass of iron and slag called ...
furnaces.
The resources necessary for production were wood for
charcoal, clay for the construction of bloomery furnaces, and water for processing.
Iron in the ore is reduced to a
spongy iron bloom that stays in the upper part of the furnace while the undesirable elements stream downwards as
slag
The general term slag may be a by-product or co-product of smelting (pyrometallurgical) ores and recycled metals depending on the type of material being produced. Slag is mainly a mixture of metal oxides and silicon dioxide. Broadly, it can be c ...
. 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. The bloom must then be consolidated with a hammer to make usable
wrought iron
Wrought iron is an iron alloy with a very low carbon content (less than 0.05%) in contrast to that of cast iron (2.1% to 4.5%), or 0.25 for low carbon "mild" steel. Wrought iron is manufactured by heating and melting high carbon cast iron in an ...
. 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.
Europe
The first iron smelting attempts date to the 2nd millennium BCE in the
Near East
The Near East () is a transcontinental region around the Eastern Mediterranean encompassing the historical Fertile Crescent, the Levant, Anatolia, Egypt, Mesopotamia, and coastal areas of the Arabian Peninsula. The term was invented in the 20th ...
.
The technology then spread throughout Europe in the following two millennia, reaching
Poland
Poland, officially the Republic of Poland, is a country in Central Europe. It extends from the Baltic Sea in the north to the Sudetes and Carpathian Mountains in the south, bordered by Lithuania and Russia to the northeast, Belarus and Ukrai ...
in the 2nd century BCE.
Iron production reached
Scandinavia
Scandinavia is a subregion#Europe, subregion of northern Europe, with strong historical, cultural, and linguistic ties between its constituent peoples. ''Scandinavia'' most commonly refers to Denmark, Norway, and Sweden. It can sometimes also ...
around 800–500 BCE. 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. The ore used was limonite in the form of red soil and bog ore. From 200 CE ore from limonite-deposits in lakes was used. The ore was reduced in bloomeries. There is evidence of a direct relationship between Viking settlements in northern Europe and North America and bog iron deposits.
Bog iron dominated the iron production of
Norse populated areas, including Scandinavia and
Finland
Finland, officially the Republic of Finland, is a Nordic country in Northern Europe. It borders Sweden to the northwest, Norway to the north, and Russia to the east, with the Gulf of Bothnia to the west and the Gulf of Finland to the south, ...
, from 500 to 1300 CE.
Large scale production of bog iron was also established in
Iceland
Iceland is a Nordic countries, Nordic island country between the Atlantic Ocean, North Atlantic and Arctic Oceans, on the Mid-Atlantic Ridge between North America and Europe. It is culturally and politically linked with Europe and is the regi ...
at sites known as "iron farms".
Smaller scale production sites in Iceland consisted of large farmsteads and some original Icelandic settlements, but these seemed to only produce enough iron to be self-sufficient.
Even after improved smelting technology made mined ores viable during the Middle Ages, bog ore remained important into modern times, particularly in peasant iron production. In
Russia
Russia, or the Russian Federation, is a country spanning Eastern Europe and North Asia. It is the list of countries and dependencies by area, largest country in the world, and extends across Time in Russia, eleven time zones, sharing Borders ...
, bog ore was the principal source of iron until the 16th century, when the superior ores of the
Ural Mountains became available.
North America
Pre-Columbian
Iron was produced by the
Vikings
Vikings were seafaring people originally from Scandinavia (present-day Denmark, Norway, and Sweden),
who from the late 8th to the late 11th centuries raided, pirated, traded, and settled throughout parts of Europe.Roesdahl, pp. 9� ...
on
Newfoundland
Newfoundland and Labrador is the easternmost province of Canada, in the country's Atlantic region. The province comprises the island of Newfoundland and the continental region of Labrador, having a total size of . As of 2025 the population ...
around 1021 CE.
Excavations at
L'Anse aux Meadows
L'Anse aux Meadows () is an archaeological site, first excavated in the 1960s, of a Norse colonization of North America, Norse settlement dating to approximately 1,000 years ago. The site is located on the northernmost tip of the island of Newf ...
have found considerable evidence for the processing of bog iron and the production of iron ore.
The settlement at L'Anse aux Meadows was situated immediately east of a sedge peat bog and 15 kg of slag was found at the site, which would have produced around 3 kg of usable iron.
Analysis of the slag showed that considerably more iron could have been smelted out of the ore, indicating that the workers processing the ore had not been skilled.
This supports the idea that iron processing knowledge was widespread and not restricted to major centers of trade and commerce.
Ninety-eight nail fragments were also found at the site as well as considerable evidence for woodworking which points to the iron produced at the site possibly being used only for ship repair and not tool making.
Colonial North America
Bog iron was widely sought in
colonial North America. The earliest known iron mines in North America are the mines from
St. John's, Newfoundland, reportedly in operation by
Anthony Parkhurst in 1578. The first mining efforts in Virginia occurred as early as 1608. In 1619
Falling Creek Ironworks was established in
Chesterfield County, Virginia. It was the location of the first
blast furnace
A blast furnace is a type of metallurgical furnace used for smelting to produce industrial metals, generally pig iron, but also others such as lead or copper. ''Blast'' refers to the combustion air being supplied above atmospheric pressure.
In a ...
facility in North America.
Lake Massapoag in
Massachusetts
Massachusetts ( ; ), officially the Commonwealth of Massachusetts, is a U.S. state, state in the New England region of the Northeastern United States. It borders the Atlantic Ocean and the Gulf of Maine to its east, Connecticut and Rhode ...
was drawn down by deepening the outlet channel in a search for bog iron. 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. The success of the Saugus Iron Works, and the rapid depletion of the region's natural bog iron, led the owners to send prospectors into the surrounding countryside. In 1658 the company bought of land which covered areas that are now Concord, Acton, and Sudbury. They set up a large production facility in
Concord, Massachusetts
Concord () is a town in Middlesex County, Massachusetts, United States. In the 2020 United States census, 2020 census, the town population was 18,491. The United States Census Bureau considers Concord part of Greater Boston. The town center is n ...
, 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.
In
Central and
Southern New Jersey
New Jersey is a U.S. state, state located in both the Mid-Atlantic States, Mid-Atlantic and Northeastern United States, Northeastern regions of the United States. Located at the geographic hub of the urban area, heavily urbanized Northeas ...
, bog ore was mined and refined for the production of naturally rust-resistant tools and
wrought iron
Wrought iron is an iron alloy with a very low carbon content (less than 0.05%) in contrast to that of cast iron (2.1% to 4.5%), or 0.25 for low carbon "mild" steel. Wrought iron is manufactured by heating and melting high carbon cast iron in an ...
rails, many of which still grace staircases in
Trenton and
Camden. During the
American Revolution
The American Revolution (1765–1783) was a colonial rebellion and war of independence in which the Thirteen Colonies broke from British America, British rule to form the United States of America. The revolution culminated in the American ...
, bog iron
cannonballs were cast for the colonial forces.
19th century United States
Bog iron was also found on the
Eastern Shore of Maryland
The Eastern Shore of Maryland is a part of the U.S. state of Maryland that lies mostly on the east side of the Chesapeake Bay. Nine counties are normally included in the region. The Eastern Shore is part of the larger Delmarva Peninsula that Ma ...
. 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.
The Shapleigh Iron Company constructed a smelter at
North Shapleigh, Maine, in 1836 to exploit a small bog iron deposit in Little Ossipee Pond. The plant commenced operation in 1837, but according to an 1854 history of Shapleigh "the business
rovedunprofitable, therefore after a few years it was abandoned."
[Weddle, Thomas K. The Iron Age of Maine, Part II: The Shapleigh Iron Company: A Foray into Industrial (geo)Archaeology in ''Maine Geologic Facts and Localities''. Augusta, Maine: Maine Geological Survey, November 2003. https://digitalmaine.com/mgs_publications/370/ accessed 6/9/2019.]
See also
*
*
*
* (iron-oxidizing bacteria)
*
References
External links
ASME PDF filewith detailed reconstruction drawings of the furnace and surroundings.
* at the Maryland Historic Trust.
*
{{DEFAULTSORT:Bog Iron
Bogs
Iron
Economic geology
Iron ores
fi:Järvimalmi