Fuller's earth

Fuller's earth is any nonplastic clay or claylike earthy material that can be used to decolorize, filter, and purify animal, mineral, and vegetable oils and greases.

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Occurrence and composition

  In 2005, USA was the largest producer of fuller's earth with almost 70% world share followed at a distance by Japan and Mexico, reports the British Geological Survey.

Fuller's earth usually has a high magnesium oxide content. In the United States, two varieties of fuller's earth are mined, mainly in the southeastern states of the United States of America. These comprise the minerals montmorillonite or palygorskite (attapulgite) or a mixture of the two; some of the other minerals that may be present in fuller's earth deposits are calcite, dolomite, and quartz.

In England, fuller's earth occurs mainly in the Lower Greensand. It has also been mined in the Vale of White Horse, in Oxfordshire, England. The Combe Hay Mine was a fuller's earth mine operating to the south of Bath Somerset until 1979. Other English sources include a mine near Redhill, Surrey (worked until 2000), and Woburn, Bedfordshire, where production ceased in 2004.

In some countries, like the UK, calcium bentonite is known as fuller's earth, a term which is also used to refer attapulgite, a mineralogically distinct clay mineral but exhibiting similar properties.

Uses

The name reflects the first use of the material. In past centuries, fullers (q.v.) kneaded fuller's earth and water into woollen cloth to absorb lanolin, oils, and other greasy impurities as part of the cloth finishing process.

Fuller's earth was also sold in pharmacies until recently for compressing pills and it is sometimes used by crane operators and their oilers to absorb grease and oil off the brake bands on the winches to make them function properly.

Fuller's earth is also used by military forces to clean soldiers who are contaminated with chemical weapons.

It also finds use in special effects when simulating explosions. Fine-grained fuller's earth makes a much larger plume than ordinary dirt, suggesting a larger explosion and allowing a smaller, safer charge to be used.

Important uses are in absorbents and filters. Because of this, fuller's earth is sometimes found in cat litter.

Hills, cliffs and slopes containing fuller's earth can be unstable, since this material can be thixotropic, when saturated by heavy rainfall.

In fly fishing, a mixture of Fuller's earth and detergent can be used to prevent undesirable flotation of a greasy fly fishing leader (the fine fishing line attached to the fly). The aim is to prevent the fish seeing it on the surface thereby becoming frightened off or "spooked".

In popular culture

An alleged fuller's earth mining operation is the subject of a Sherlock Holmes mystery, The Adventure of the Engineer's Thumb

See also

• Bentonite
• Sepiolite

References

• British Geological Survey, Mineral Fact Sheet: Fuller's Earth [1] (accessed 16 November 2006).
• "fuller's earth". Encyclopædia Britannica Encyclopædia Britannica Online. (2006). 9035638. Retrieved on 2006-11-02. 
• Oxford English Dictionary, Second Edition. Oxford: Oxford U P, 1989.