The Conodont Alteration Index (CAI) is used to estimate the maximum temperature reached by a sedimentary rock using thermal alteration of conodont fossils. Conodonts in fossiliferous carbonates are prepared by dissolving the matrix with acid, since the conodonts are composed of apatite and thus do not dissolve. The fossils are then compared to the index under a microscope. This article or section does not adequately cite its references or sources. ... Metamorphism can be defined as the mineralogical, chemical and crystallographic changes in a solid-state rock, i. ... Conodonts are extinct worm-like forms with distinctive conical or multi-denticulate teeth made of apatite (calcium phosphate). ... Carbonate is an anion with a charge of -2 and an empirical formula of CO32-. An aqueous solution of carbon dioxide contains a minute amount of H2CO3, called carbonic acid, which dissociates to form hydrogen ions and carbonate ions. ... ske| Fracture|| Conchoidal to even Apatite is a group of phosphate minerals, usually referring to hydroxylapatite, fluorapatite, and chlorapatite, named for high concentrations of OH-, F-, or Cl- ions, respectively, in the crystal. ...

The CAI ranges from 1 to 6, as follows:

The CAI is commonly used by paleontologists due to its ease of measurement and the abundance of Conodonta throughout marine carbonates of the Paleozoic. However, the organism disappears from the fossil record after the Permo-Triassic extinction, so the CAI is not available to analyze rocks younger than 250 million years. Additionally, the index can be positively skewed in regions of hydrothermal alteration. Celsius is, or relates to, the Celsius temperature scale (previously known as the centigrade scale). ... The Paleozoic Era (from the Greek palaio, old and zoion, animals, meaning ancient life) is the earliest of three geologic eras of the Phanerozoic eon. ... Metamorphism can be defined as the mineralogical, chemical and crystallographic changes in a solid-state rock, i. ...

External links

Table of CAI from Königshof 2003, with photographs