- Name also: Arctic Blue
- Latin synonym: Plebejus glandon
- Family: Gossamer-winged Butterflies – Lycaenidae
- Subfamily: Blues – Polyommatinae
- Wing span: Very small, 20–25 mm (0.78–0.98 in.). Females usually larger than males.
- Wing upper side: Pale greyish blue, with unclear dark margin which is often fragmented on the hind wing into separate blotches. Females can be almost graphite grey and the edges and leading parts of their wings have light-coloured patches. Both forewing and hind wing have a distinct black blotch in the middle.
- Wing underside: Pale grey-dark brownish grey. Forewing with white-edged black blotches, hind wing with light-coloured blotches.
- Habitat: Stony precipices above the tree line.
- Flying time: Early July.
- Overwintering form: Caterpillar.
- Larval foodplant: Apparently purple saxifrage (Saxifraga oppositifolia) and yellow mountain saxifrage (S. aizoides).
- Endangerment: Endangered, protected in all of Finland.
In Finland the best (and usually only) place to find the Glandon blue is among the crumbling, calciferous slate and minerals where mountain avens grows at least 700 metres up the slopes of Saanatunturi Fell.
The Glandon blue is the second smallest of blues in Finland (the smallest one is Little blue, Cupido minimus). The Glandon blue is easy to differentiate from other butterflies due to the greyish blue or graphite grey colour of the upper side of its wing, and the light patches on the underside of its hind wing. Males fly close to the ground looking for females. The species overwinters as a small caterpillar and cocoons itself in cracks or between stones.