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Sedimentary Rocks - Limestone.
Limestone is an example of a sedimentary rock
which has not formed from the
processes of weathering.
Limestone comes from the remains of millions
of sea creatures
which have died and fallen to the bottom
of the sea.
The creatures themselves have decayed but their shells and skeletons
remain.
Compaction over
millions of years turn these remains into limestone rock.
Limestone is mainly calcium carbonate. It has many uses.
Other examples of sedimentary
rock not formed by weathering
are chalk, coal and rock
salt.
Chalk
is a very pure form of calcium carbonate,
and is made in a similar way to limestone.
The formation of coal is outlined in the section Products from Oil.
Rock
salt is formed from salts which have crystallised out of sea water
as the water has evaporated.
The process is the same as that given
for general crystallisation where
evaporation of water from a saturated
solution causes the salt to
crystallise.
The salt crystals will
then settle as a sediment,
and compaction turns the salt into a sedimentary rock.
Rock salt
is mainly sodium
chloride.
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