A dazzling diamond of Indian origin that belonged a member of a European royal family sold for $21.5 million at a Christie’s auction in Geneva, Switzerland, on Tuesday.

The white stone, named after Archduke Joseph August of Austria (1972-1962) stands out for its size, its clarity and its historical importance. The price it attracted at the auction was a world record for a colorless diamond. Christie’s had expected the diamond, which weighs a whopping 76.02 carats, to sell for between $15 million and $25 million.

It didn’t disclose the name of the buyer....