It has a universal veil that can vary in prominence, and is yellow when young, later turning brown, and slightly sticky.

[4] Calonarius osloensis has crowded, 3-6 mm wide, yellowish gills, with slightly scalloped to serrated edges.

[1] It forms mycorrhiza with small-leaved linden trees, in calcareous (calcium-carbonate rich), shallow, soils with little leaf litter or humus.

Threats to the species include the decline of calcareous linden forests due to the land being developed for residential areas, or limestone quarries.

Additionally, the invasion of Picea abies (Norway spruce) trees from adjacent plantations, as well as increased thickets of Ash and Maple, cause the soils to become more humid and acidic.

The cap of Cortinarius langeorum is stained dark red by KOH, and its gills are gray rather than yellow, which distinguishes it from Calonarius osloensis.