A small succulent plant proliferating from the base to form dense rounded clusters up to 250 mm in diameter. The roots are up to 2 mm thick. The leaves at first grow in two opposite rows (distichous), later becoming a dense rosette. They are 50-70 mm long and 15-18 mm in diameter at the base, firm but brittle, tongue-shaped, tapering towards the ends, straight but sometimes sickle-shaped (falcate), ending in an acute sharp point (mucronate). The inner leaves grow erect, the outer ones are spreading. Their upper surface is flat, becoming slightly channelled during dry conditions. The lower surface is rounded at the base but has a distinct keel. They are grey-green (glaucous) and rough due to raised tubercles.

The leaf margins are beset with horny white tubercles. When becoming detached the leaves will root and form new plantlets.The inflorescence is a simple raceme up to 250 mm long. The flowers are tubular and pendulous (hanging downwards) on stalks up to 7 mm long. The flowers are 30-43 mm long, with the belly-shaped (gasteriform), reddish pink basal portion up to 10 mm in diameter; the narrow upper portion is greenish yellow to yellow. After fertilization, the flower stalks (pedicels) become stiff, and the capsules, which are oblong and up to 20 mm long and 8 mm in diameter, are held erect. The flattish seeds are blackish, 3 mm long and 2 mm wide.

Gasteria glauca differs from other species of the genus by its leaves which are distinctly glaucous (grey-green) and often sharply pointed. It is related to G. ellaphieae, a well camouflaged crevice dweller from the Kouga Dam area and further to the east.