 Advanced carbonation of felsic and mafic rocks, very rarely, creates fenite, a metasomatic alteration caused particularly by carbonatite intrusions.Fenite alteration is known, but very restricted in distribution, around high-temperature metamorphic talc-carbonates, generally in the form of a sort of aureole around ultramafics.Such examples include biotite-rich zones, amphibolite-calcite-scapolite alteration and other unusual skarn assemblages.