A quote from the French naturalist, Cuvier (1827)

The Blue Antelope. (A. leucophaea) The Blue Antelope, or Blauw Bock of Kolbe, was formerly not uncommon in the vicinity of Swellendam, in the Cape Colony, but now so rare, that no specimen has been killed in South Africa since the year 1799. Mr Allaman first described and figured it from the spoils of one shot by Colonel Gordon, under the wrong name of Tseiran, or Dzeren, which belongs to a smaller species of Asia. It is an animal of considerable beauty, four feet high at the shoulder, and above six feet in length; the horns are slightly compressed, and assume the curve of a scimitar, measuring twenty-eight inches along the curve; at the base they are closely wrinkled, numbering from twenty to thirty annuli, without appearance of striae; the ears are long and pointed, gray at the back, and white within; a white spot passes before each eye, extending downwards towards the mouth; the forehead and chaffron are dark gray, as also the anterior part of the legs; the inside of the limbs is white: but what distinguishes the animal most, is the silvery blue-gray of his coat, occasioned by the hair, which is rather long and coarse, lying sparingly scattered upon a shining black hide, which is also the cause why the beauty of this colour fades into a duller gray after death, the skin becoming browner with drying.

There is a short mane of reversed white hair on the neck, and the muzzle is black, but the beard ascribed to it by Kolbe is more doubtful, because not observed in the figures of specimens, though it is not improbable that the long hairs composing it are inclined to drop out from the skins, or perhaps only remarkable in the rutting season, and wanting in the females.

The manners of the species are totally unknown, and the horns are rare in cabinets of natural curiousities. The only specimen now known is in the Museum of Paris, whither it was brought, we believe, from the collection of the late stadtholder of Holland. We possess a drawing of the individual, which, however, is far inferior in beauty to another which we copied from the original drawn by Colonel Gordon, a duplicate of which appears figured in the works of Count de Buffon.

Cuvier's Animal Kingdom, IV. Mammalia. 1827:176