Limestone Essay

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Limestone:
What is limestone?
Limestone is a sedimentary rock that is widely found in New Zealand. The rock is made up of more than 50% calcium carbonate (CaCO3) which is derived from the shells of tiny marine fossils. Limestone commonly forms in shallow marine water from a build-up of marine organism’s fossils. In the Waikato there are two major quarries where limestone is formed, one in Te Kuiti and another in Otorohanga which is near where the Waitomo Caves are based. In this report, I will be investigating and analysing the chemical processes involved with the formation of limestone caves, and the consequences these chemical processes pose on the environment.
Formation of limestone:
In New Zealand most limestones are made of shell fragments and lime muds which were originally deposited in the shallow marine waters. These fragments are loose sediment, which undergoes diagenesis to form a hard sediment rock of limestone. The loose sediment is buried beneath the ground, which applies a lot of pressure to the calcium carbonate sediment. This application of pressure is called pressure dissolution. Through this pressure the calcium carbonate actually starts to dissolve. It then seeps into the pores and reprecipitates as cement, which provides the solid characteristic of limestone.
Formation of limestone caves:
Limestone is formed when carbonic acid reacts with the limestone bedrock. However, we first must look at how this carbonic acid was formed: Co2 + H2O H2CO3 . The word for this equation is Carbon dioxide + Water Carbonic Acid. This reaction occurs when the evaporated water combines with the carbon dioxide in the atmosphere to produce carbonic acid. Include soil Co2
The carbonic acid lea...

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...in the cave’s atmosphere. The air we breathe contains carbon dioxide, therefor the Waitomo Cave’s decision to limit the amount of visitors to certain caves each day, is a great way to reduce the impact on the equilibrium. (http://books.google.co.nz/books?id=IBESYmQcb0sC&pg=PA119&lpg=PA119&dq=chemical+equilibrium+in+caves&source=bl&ots=XQ9_hSQ5GP&sig=0i8oZ2ZIAyqHOSKd9R2wr3yo7_I&hl=en&sa=X&ei=gLB4U53tMbKp7AbSwIGQBA&ved=0CCcQ6AEwAA#v=onepage&q=chemical%20equilibrium%20in%20caves&f=false)
Another impact on caves is the extensive road works and agriculture to produce an urban lifestyle. Water is huge part in the formation process of caves and mineral crystallites. Through toxic chemicals produced from urbanization, this water is contaminated and poses a threat to the continuity of the caves.
(http://www2.nature.nps.gov/views/KCs/CaveKarst/HTML/ET_Threats.htm)

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