Carbonatites

Carbonatite

Igneous rock
Carbonatite from Jacupiranga, Brazil. This rock is a compound of calcite, magnetite and olivine
Composition
Primary	carbonate minerals, (> 50%)
Secondary	Other

Carbonatite (pronunciation: /kɑːrˈbɒnətaɪt/) is a type of intrusive or extrusive igneous rock defined by mineralogic composition consisting of greater than 50 percent carbonate minerals. Carbonatites may be confused with marble, and may require geochemical verification.

Carbonatites usually occur as small plugs within zoned alkalic intrusive complexes, or as dikes, sills, breccias, and veins. They are, almost exclusively, associated with continental rift-related tectonic settings. It seems that there has been a steady increase in the carbonatitic igneous activity through the earth's history, from the Archean Eon to the present.

Nearly all carbonatite occurrences are intrusives or subvolcanic intrusives. This is because carbonatite lava flows, being composed largely of soluble carbonates, are easily weathered and are therefore unlikely to be preserved in the geologic record. Carbonatite eruptions as lava may therefore not be as uncommon as thought, but they have been poorly preserved throughout the Earth's history.