What is the mineral composition and formation of carbonatite?

Carbonatite is an unusual type of intrusive or extrusive igneous rock defined by a mineralogic composition consisting of greater than 50% carbonate minerals such as calcite, ankerite, or dolomite. They typically occur as small plugs within zoned alkalic intrusive complexes, dikes, sills, breccias, and veins, and are almost exclusively associated with continental rift-related tectonic settings. Because carbonatite lavas are composed largely of soluble carbonates, they weather easily and are poorly preserved in the geological record, making active examples like Tanzania's Ol Doinyo Lengai extremely rare.

What we know

• Carbonatite is an intrusive or extrusive igneous rock defined by a mineralogic composition consisting of greater than 50% carbonate minerals. [1, 2]
• Carbonatites usually occur as small plugs within zoned alkalic intrusive complexes, or as dikes, sills, breccias, and veins, and are almost exclusively associated with continental rift-related tectonic settings. [2]
• Carbonatite lava flows are composed largely of soluble carbonates, causing them to weather easily and remain poorly preserved throughout the geologic record. [2]
• Ol Doinyo Lengai in Tanzania is the only known carbonatite volcano to have erupted in historical time, producing cool natrocarbonatite lava. [2]

Still open

• The precise reason why certain late-stage blocks of carbonatite-glimmerite are barren of apatite remains unknown, though it could be related to metamorphism and fluid flow.

Where to go next

• a case in pointWhich active volcano erupts carbonatite lava?
• what caused itHow do tectonic settings influence carbonatite formation?
• the bigger pictureWhat are the characteristics of igneous rocks?
• how we knowHow does geochemical verification distinguish carbonatite from marble?
• whenHow has carbonatitic igneous activity changed over Earth's history?
• an unexpected connectionHow does an ancient carbonatite complex operate as a modern phosphorus mine?An extraordinarily old carbonatite formation dating back billions of years serves as the European Union's sole operating phosphorus mine, extracting apatite from glimmerite-carbonatite series rocks.

Sources

• [1]carbonatite (Wikidata Q195178) · CC0 1.0
• [2]Carbonatite · CC BY-SA 4.0
• [3]Siilinjärvi carbonatite · CC BY-SA 4.0
• [4]Zircon · CC BY-SA 4.0
• [5]Ore · CC BY-SA 4.0