Adults reach up to 5 cm in length and appear black from the distance, but dark green metallic sheen is apparent from up close. When at rest, the characteristic narrow white band between 2nd and 3rd abdominal segments is also noticeable. Other members of the genus Somatochlora also share these characters, especially the northern emerald (S. arctica) and the treeline emerald (S. sahlbergi); although, the latter lives far north and its range doesn't overlap the alpine. The northern emerald has olive-green eyes (compared with azure in the alpine emerald) and less contrasting white band, but closer examination of anatomical characters, especially on the legs, is necessary for reliable determination.