Page 10 - Curriculum Visions Dynamic Book

Limestone
Limestone is the common name for rocks
that are made up mainly of calcium carbonate. Limestones vary greatly and have many origins.
The origins of limestone
Most limestone rocks share an origin in ancient warm, shallow seas. Some were formed as vast coral reefs. Others were formed from the cemented remains of tiny sea creatures and made into soft chalk. The warm waters also caused calcium to precipitate out from sea waters rather like the scale in a kettle. This scale took the form of millions of tiny balls of limestone. This type of limestone is called oolitic limestone after the Greek word oon, meaning egg-shaped.
Water-bearing rocks
Most limestones have cracks and gaps that make them porous. Oil and water can then accumulate in these gaps. This is what makes limestone good oil- bearing and water-bearing rock.
The colour of limestone
Limestone is rarely white because of the impurities in it. It is most commonly light grey, a result of a mixture of calcite and mud. Oolitic limestone is often honey- coloured because it contains some
iron. Limestones can contain so much iron that they are worth mining as iron ore.
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