‘Green rusts’ are a group of reduced Fe hydroxides with a pyroaurite-like structure. In a new occurrence, green rust is present as a 45–60 mm thick band which lies just below the surface (~4 mm) of an ochreous deposit at an abandoned coal mine site. The sample is characterized by the presence of μ m-sized hexagonal crystals which have been identified from SEM imaging. Chemical analyses reveal an Fe(II):Fe(III) ratio which is close to the characteristic 2:1 ratio, and XRD analysis identifies the material by characteristic lattice spacings. The green rust layer also contains aragonite which is not present in the surrounding ochre. Green rusts are important as they have the potential to be used in water treatment.