Can a Rock Rot? The answer is yes! If you have ever looked at a china clay pit and seen the soft, white, sticky china clay it is hard to imagine that it was once a hard rock. For example, the china clay found in South Devon, England is the result of the rotting of the granite underlying the moors of Dart moor and Bodmin.
But what happens to make the granite rot into clay? Rocks rot by the process known as weathering, and all rocks suffer from its effect whether they are found in the tropics or the frozen wastes of the Antarctic. Weathering is the sum total of all the effect on the surface materials caused by the processes of heating and cooling freezing and thawing and so on.
There are two main types of weathering given special names by geologists:
Physical weathering: These are the processes by which rocks are broken down by action such as change of temperature on the materials themselves, and also the effects of water freezing and thawing in contact with the rocks.
- Chemical weathering: This is the term used to describe what happens when the chemicals that make up the rocks change as a result of the action of weather and air.
It is also worth noting that plant growth can have a considerable effect on rock materials, as can bacteria – a tiny organism which is not like any other plant or animal. In fact, without these bacteria which release essential nourishment from the rocks, there could be no more advanced life forms including man himself.
In areas of the world where it is damp enough to have rain and become cold enough for the water to freeze, rocks can be prised apart by the action of ice as it freezes and expands. In hot, dry deserts rocks may become very hot during the day only to cool very quickly as soon as the sun goes down so that they expand and shrink suddenly. This can cause the rocks to split with explosive force. Chemical weathering
When rain falls it may carry gasses from the air such as oxygen and carbon dioxide. The carbon dioxide makes the rains slightly acid; acid enough to be able to dissolve rocks like limestone. The Karts district of Yugoslavia, for example, where the rocks are worn into blocks and channels and swallow holes and caves, show the effects of this very well.
You have seen, then, that, like a piece of wood or an apple, a rock can become rotten when its materials may fall victim to rain and the wind.
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