The lichen forms a thin to moderately thick crust that spreads widely over its rock substrate. Its surface is dark grey with a bluish cast and breaks into coarse, irregular polygonal blocks known as s. These blocks are dusted with masses of minute powdery propagules—technically called
soredia or —each about 25–50
micrometres (μm) across. Because the soredia originate around the margins of the areoles and then blanket the entire surface, the thallus acquires a granular, flour-like appearance. Fruiting bodies (
apothecia) are uncommon and small, rarely exceeding 1.5 mm in diameter. They lie partly submerged among the , bordered by a thick, grey rim derived from the thallus itself. The central ranges from bright yellow to dull orange and may become slightly domed with age. Inside each disc, unbranched threads of fungal tissue (
paraphyses) end in tips that swell to about 5 μm wide. The
asci produce eight colourless
ascospores, each 10–15 μm long and 5–7 μm wide, divided by a cross-wall (
septum) about one-third of the spore's length. In standard chemical
spot tests, the thallus turns a faint violet when treated with
potassium hydroxide solution (the K-test), whereas the apothecial disc reacts a deeper purple, helping confirm the identify of the species in the field. ==Habitat and distribution==