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Limestone
1930s was the result of light soils blowing. The same happens in Victoria, Australia, creating dust- laden winds called a buster or brickfielder. (Contrast with: Heavy soil.)
Limestone fossil
Limestone rock
Limestone
A sedimentary rock in which more than half the material is calcium carbonate (calcite).
There is a wide
variety of limestones.
Some, like chalk, are quite
soft, while others, like
so-called mountain limestone, are so hard they can be used as the foundations for roads.
All limestones react easily with acids (see: Chemical weathering and Weathering) and are therefore much more readily eroded in humid climates than in desert climates. In a desert, limestones behave as just another hard rock, while in humid climates limestones may erode chemically faster than other rocks.
Many limestones are grey and appear to be massive. Others have fractured into blocks. If these fractured blocks are exposed at the surface, water can seep into them and dissolve the faces of
the blocks. These bare surfaces with widened cracks are called limestone pavements.
Solution does not stop at the surface. It also occurs below
the surface and affects wherever water flows through limestone. In time huge amounts of limestone can be eroded away, leaving an underground landscape of caves and tunnels.
Limestones are formed in many different environments. Some appear in seas that contain very
Crystals of calcite
 Limestone – Limestone can be found as rock, as fossils and as the mineral calcite.
little sediment. In this case the limestone rock is almost pure white. Others emerge in a sea in which there is a large amount of clay. The combination of calcium carbonate and clay creates a grey limestone.
The calcium carbonate of most limestones comes from the skeletons of sea organisms. Chalk is entirely made from the skeletons of microscopic sea creatures. Many limestones also contain remains
of larger creatures such as corals, mollusks and sea urchins. These fossils can all be used to identify the rocks.
When cut and polished, hard limestones containing large fossils can be extremely decorative and are used for floors of buildings.
(See also: Formation.)
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