Octahedral Diamond

Diamond. 2.5 x 2.5 x 1.5 cm. South Africa. 1898.

The largest diamond in the Vienna collection is remarkable not only for its 82.5 carats, but also for its purity and perfect octahedral shape.

82.5 CARATS
The diamond was a gemstone valued for its hardness and fire even in Antiquity, as documented by Plinius in his Historia naturalis: “The greatest value, not only amongst precious stones, but of all human possessions, is attributed to the diamond, long known to only kings, and then to very few of them … of indescribable hardness, and even able to conquer fire, hence the name ‘adamas’, which means ‘invincible’ in Greek.”
Diamonds consist of pure crystallized carbon, and the fact that they are combustible was demonstrated only in the 18th century, not least by Emperor Franz I Stephan of Lorraine. The fact that diamonds are easily split regardless of their hardness was realized much earlier, and this discovery led to the production of diamond powder, one of the uses of which is for cutting diamonds.
The octahedral diamond caused a sensation at the 1898 Imperial Jubilee Exhibition in the Prater due to its 82.5 carats (16.5 grams), its purity, and its perfect crystal shape. Even the emperor himself admired this exceptional gemstone. Soon afterwards it was offered to the mineralogical department of the imperial and royal Natural History Museum, but the chief chamberlain declined to purchase it. Then in 1899 a “generous benefactor” in the person of factory owner Georg von Haas donated this “extremely precious exhibit of supreme quality” to the museum. The slightly yellow gemstone was considered to be “the largest diamond crystal currently contained in a mineralogical collection.” However, they overlooked the fact that the British Museum of Natural History had had a 133 carat diamond on show ever since 1887.