Chlormayenite (after Mayen, Germany), Ca12Al14O32[☐4Cl2], is a rare calcium aluminium oxide mineral of cubic symmetry.

It is also found at pyrometamorphic sites such as in the Hatrurim Formation of Israel and in some burned coal dumps.

[6][3] It occurs in thermally altered limestone xenoliths within basalts in Mayen, Germany and Klöch, Styria, Austria.

It occurs with calcite, ettringite, wollastonite, larnite, brownmillerite, gehlenite, diopside, pyrrhotite, grossular, spinel, afwillite, jennite, portlandite, jasmundite, melilite, kalsilite and corundum in the limestone xenoliths.

[4][7] The formula can be written as [Ca12Al14O32]O,[8] which refers to the unique feature: anion diffusion process.