Carbonatite

Carbonatite () is a type of igneous rock. It has greater than 50% carbonate minerals. Carbonatites may be confused with marble, so may need geochemical analysis to make sure.
Carbonatites usually occur as small plugs, or as dikes, sills, breccias, and veins. They are almost all near or in 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. Carbonates in general are typical products of life-forms.