Re: How is 'bog iron' formed?

Hi Arnold, Thanks for the question. Bog iron is a mineral iron ore also known as limonite. It forms under oxidizing conditions, because reduced iron (ferrous iron or Fe(II)) is soluble, whereas oxidized iron (ferric iron or Fe(III)) is insoluble. The oxidization can be entirely chemical-reduced iron is formed by iron-reducing bacteria which can derive energy from the process, in anaerobic habitats. It's then carried by groundwater to oxygenated habitats where it oxidizes and precipitates. But the process can be accelerated by so-called iron oxidizing bacteria.

Chemically, the soluble form of iron is often iron (II) carbonate. When water accumulates in bogs and marshes, evaporation causes loss of the carbonate as CO₂ and the hydrated oxide, limonite forms. The formula of limonite is:
Fe₂O₃.3H₂O

Iron-oxidizing bacteria are bacteria that can accumulate iron(II) and oxidise it to iron (III). Often they reduce sulphate to sulphide in the process, resulting in the foul smell often found in stagnant water and bogs. There are many kinds of iron-oxidizing bacteria, some of which are unidentified, but one of the best known is called Thiobacillus ferrooxidans.

Bog iron can form anywhere where the conditions are suitable, so I'm sure this includes S. Maine, but I don't know if there are any notable deposits in this area. And finally, bog iron can't be brought up with a magnet- only pure iron metal and certain ores are magnetic in this way.

Here are some websites you might like to look at:

htt p://www.ce.vt.edu/enviro2/gwprimer/bacteria/bacteria.html
A good introduction to the many bacterial processes in groundwater.

http://osf1.gmu.edu/~jwe iss/webdoc3.htm
Research into iron oxidization around plant roots.

http://www.pre ssplus.com/pinelands/land/iron.html
Bog iron in the NJ Pinelands.

http://www.smenet.org/opaque-ore/ix_t_6.htm
Virtual atlas of opaque and ore minerals.

Neil Saunders