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What are clays and clay minerals?
Clay
minerals are the fine-grained components of geological materials, occurring
mostly as particles with a phyllosilicate or sheet
structure with diameters ranging from a few microns to a few hundredths of a
micron. They tend to have large surface areas, often high cation
exchange capacities, high adsorption capacities and some have swelling
properties, all of these characteristics making clays fascinating materials for
study and giving them properties which are important
from many viewpoints, academic and applied. Most of the common clay minerals
belong to the following groups: kaolinite-serpentine,
pyrophyllite-talc, smectite, vermiculite, mica,
chlorite and sepiolite-palygorskite.
Clay
minerals are important in a number of geological applications such as stratigraphic correlations, indicators of environment of
deposition and temperature for generation of hydrocarbons. They also form an
important constituent of soils where they exert a dominant influence on soil
structure and plant nutrition. In industry, they are used in drilling muds, coatings and fillings in paper manufacture, ceramics,
brick and tile manufacture and many other applications. A
"clay" as opposed to a "clay mineral" is often a
chemically very heterogeneous and structurally complex mixture of colloidal
particles including clay minerals mixed with finely divided quartz, feldspars,
carbonates, oxides and hydroxides of Al and Fe and organic matter.
Below
are some links to sites which contain further information:
http://www.minsocam.org/MSA/collectors_corner/arc/nomenclaturecl1.htm
http://www.mii.org/Minerals/photoclay.html
http://www.webref.org/geology/c/clay_minerals.htm
http://minerals.usgs.gov/minerals/pubs/commodity/clays/
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