Editing Diamond (section)

=== Formation and growth ===
[[File:Diamond age zones.jpg|thumb|Age zones in a diamond<ref name=DCOdecadal/>]]
Diamonds in the mantle form through a ''[[metasomatism|metasomatic]]'' process where a C–O–H–N–S fluid or melt dissolves minerals in a rock and replaces them with new minerals. (The vague term C–O–H–N–S is commonly used because the exact composition is not known.) Diamonds form from this fluid either by reduction of oxidized carbon (e.g., CO<sub>2</sub> or CO<sub>3</sub>) or oxidation of a reduced phase such as [[methane]].<ref name=Cartigny/>

Using probes such as polarized light, [[photoluminescence]], and [[cathodoluminescence]], a series of growth zones can be identified in diamonds. The characteristic pattern in diamonds from the lithosphere involves a nearly concentric series of zones with very thin oscillations in luminescence and alternating episodes where the carbon is resorbed by the fluid and then grown again. Diamonds from below the lithosphere have a more irregular, almost polycrystalline texture, reflecting the higher temperatures and pressures as well as the transport of the diamonds by convection.<ref name=Shirey2013/>