Bog iron

Bog iron is a form of impure iron ore found in bogs or swampy areas. It is a type of limonite (hydrated iron(III) oxide) that forms through a natural chemical process involving the precipitation of iron from groundwater.

Formation occurs when groundwater, enriched with dissolved iron, seeps into oxygen-rich bog environments. The iron, usually in the ferrous (Fe²⁺) state, is oxidized to the ferric (Fe³⁺) state. This ferric iron is less soluble and precipitates out of the water, forming iron oxides and hydroxides. Organic matter in the bog, such as decaying vegetation, plays a role in the process, sometimes contributing to the reduction of iron and influencing the ore's composition.

Bog iron is typically porous and contains a significant amount of impurities, including sand, clay, and organic matter. Its iron content is generally lower than that of other iron ores, making it a less desirable source for modern steel production.

Historically, bog iron was an important resource, particularly in areas where higher-grade iron ores were scarce. It was relatively easy to extract and smelt using simple techniques, making it valuable for local blacksmithing and iron production. Many early ironworks, especially in regions with abundant bogs, relied on bog iron as their primary source of iron. The resource contributed significantly to early industrial development in those areas.

The extraction of bog iron often involved dredging it from the bog bottom or excavating it from shallow deposits. After extraction, the ore was typically roasted to remove water and organic matter before being smelted in a furnace.