A crustose species with a grey, greenish grey to black thallus that is effuse or sometimes even evanescent. The thallus may be areolate and may have a black prothallus. The small, matt black apothecia are flat or convex and may have a thin margin.
Catillaria chalybeia is most common in coastal and lowland Scotland where it is found on siliceous rocks and walls, especially where nutrient-enriched or becoming basic, particularly near the sea and in churchyards. BLS distribution map
scottishlichens.co.uk 