Limestone, a fizzy rock – key terms
Exploring limestone’s geology, biology, chemistry and uses.
Limestone is the rock that fizzes with acid. It has a biogeochemical origin, a rich agricultural history and is literally ‘fizzing’ with uses and applications. This resource provides explanations of the key concepts encountered when exploring limestone – the ‘basics’ that every student should understand.
Sedimentary rock
A type of rock formed after the deposition, compaction and cementation of sedimentary material produced by either the weathering and erosion of the Earth’s surface, biological organisms (shells) or chemical precipitation (ooids). Limestone is a sedimentary rock.
Diagenesis
The hardening of loose sediment into sedimentary rock. It is the sum of the physical, chemical and biological changes that take place in sediments as they become consolidated into rocks.
Limestone
A sedimentary rock with a calcium carbonate content of no less than 50%. Its origins can be traced back to either chemical or biochemical processes that occurred in the geological past.
Geologic time scale
The time that has elapsed from the formation of the Earth to the present day. It is divided into eons, eras, periods, epochs and ages. Waitomo limestone dates to the Oligocene epoch 23–34 million years ago.
Biochemical limestone
A sedimentary rock formed from broken-up, calcium carbonate-rich skeletons (shells) of once-living marine organisms that have been cemented together.
Temperate limestone
A category of limestone, rich in the mineral calcite, that has formed from the smashed up calcareous skeletal debris of marine organisms (both plants and animals) that once lived in cool or temperate waters of higher latitudes.
Tropical limestone
A category of limestone, rich in the mineral aragonite, that has formed in warm tropical waters either from marine organisms, such as reef-building corals, or from chemically precipitated grains of calcium carbonate.
Karst landscape
Distinctive surface and underground landforms such as caves, fluted rock outcrops and dolines or sinkholes that are sometimes associated with limestone regions. The Waitomo region around Ōtorohanga is typical karst countryside.
Limestone calcination
Heating limestone to a high temperature (above 850°C) such that it decomposes into carbon dioxide and calcium oxide (lime).
Lime
Pure lime is calcium oxide, which is produced industrially by strongly heating limestone. Its ease of manufacture and chemical properties make it an important industrial chemical.
Agricultural lime
Ground-up limestone, rich in calcium carbonate, that is spread on pasture and added to soils to increase the pH of the soil.
Biomineralisation
The process by which living organisms produce minerals, often to harden or stiffen existing tissues. For example, pāua grow a protective shell based on two mineral forms of calcium carbonate known as aragonite and calcite.
Tectonic plate boundary
The margin formed when tectonic plates collide. For example, off the east coast of the North Island, the Pacific plate and the Australian plate are colliding, giving rise to the boundary known as the Hikurangi Margin.
Hikurangi Margin
An active subduction zone extending off the east coast of the North Island where the Pacific and Australian plates collide – the Pacific plate is forced down under the Australian plate.
Cold seep
A place on the seafloor where cold methane-rich water escapes. They occur most often at tectonic plate boundaries. Carbonate deposits and specialised communities of organisms are often found at these sites.
Chemosynthesis
The production of carbon-based compounds using the energy released from chemical reactions instead of the energy from sunlight. For example, chemosynthetic bacteria found at cold-seep sites use dissolved methane as their energy source.
Read this article for an introduction to this subject and the resources we have on it.
