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ראשון, 17 פברואר 2008 |
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 Clay
is a naturally occurring material composed primarily of fine-grained
minerals, which show plasticity through a variable range of water
content , and which can be hardened when dried and/or fired. Clay
deposits are mostly composed of clay mineralsphyllosilicate minerals),
minerals which impart plasticity and harden when fired and/or dried,
and variable amounts of water trapped in the mineral structure by polar
attraction. Organic materials which do not impart plasticity may also
be a part of clay deposits. ( Clay minerals are typically formed over
long periods of time by the gradual chemical weathering of rocks
(usually silicate-bearing) by low concentrations of carbonic acid and
other diluted solvents. These solvents (usually acidic) migrate through
the weathering rock after leaching through upper weathered layers. In
addition to the weathering process, some clay minerals are formed by
hydrothermal activity. Clay deposits may be formed in place as residual
deposits, but thick deposits usually are formed as the result of a
secondary sedimentary deposition process after they have been eroded
and transported from their original location of formation. Clay
deposits are typically associated with very low energy depositional
environments such as large lake and marine deposits.
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Last Updated ( רביעי, 11 פברואר 2009 )
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