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Chemical rock
A rock produced by chemical precipitation (for example, rock salt, halite). Most of these rocks form in the bottoms of lagoons
or inland lakes when mineral-rich water evaporates, leaving the minerals behind. The salt lakes
of Utah and neighbouring states have many such deposits and some of them are mined. In Poland
salt deposits are so thick that a cathedral has been carved from salt in one of the mines.
Chemical weathering
Chemical weathering
The decay, or rotting, of a rock through the chemical action of water containing dissolved acidic gases.
Most rainwater has gases dissolved in it. They combine with the water to make it weakly acid. This is the reason why chemical weathering is important in all but deserts. The process is normally very slow, except with very reactive rocks such as limestone.
Chemical weathering occurs on the surface of a rock, as
acidic water reacts with the minerals. Some of the substances produced are soluble and are carried away by the rain, while others are insoluble and remain behind. The main insoluble material is called clay.
 Chemical weathering – Chemical action works from the outside in, producing
a kind of onion-skin effect surrounding the remains of the unweathered rock.
 Chemical weathering – Take a small piece of chalk, and put it in a glass with some vinegar. The vinegar is an acid, so the chalk will slowly disappear.
 Chemical weathering – When a rock has been chemically weathered, it has no strength and breaks up as soon as it is dropped.
Vinegar
Chalk
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