English: Simplified cartoon showing the distribution and forms of carbon inside Earth. Carbon has low solubility in mantle minerals; hence, it occurs primarily in the form of gas (red circles), fluids or melts (orange circles), and accessory solid phases (green circles), including diamonds (octahedra). Reactions involving carbon include redox melting (diamond consuming) and freezing (diamond producing), reduction of carbonate to diamond, growth of diamond from metallic liquids, breakdown of carbonate under reduced conditions, redox reactions that produce tetracarbonates, and reactions between carbonate and silicate. Numbers indicate the depth at which important phase transitions in carbonates have been proposed to occur: (1) calcite to aragonite (2) dolomite to dolomite-II (3) aragonite to post-aragonite (4) dolomite-II to dolomite-III (5) Fe-carbonate to Fe-tetracarbonate (6) post-aragonite to CaCO₃ with sp3-hybridized carbon, and (7) magnesite to magnesite-II. Ferrous iron in carbonate undergoes a HS to LS transition in the mid-mantle. The thickness of the crust and slab is vertically exaggerated for clarity. Please consult Carbon-Bearing Phases throughout Earth’s Interior for references and more information.