NEW YORK (Commodity Online): A 32.01-carat emerald-cut diamond that billionaire philanthropist Leonore Annenberg bought for her 90th birthday sold for $7.7 million at an auction.

The flawless, colourless diamond sits on a ring designed by Manhattan jeweler David Webb. It is flanked by two pear-shaped diamonds, one of them 1.61 carats and the other 1.51 carats.

The ring was offered for sale by Annenberg’s estate. Christie’s auction house did not identify the buyer.

Annenberg died in March at the age of 91. She served as US chief of protocol during President Ronald Reagan’s first term — a position that carried the rank of ambassador. Her husband, Walter Annenberg, a billionaire publisher and ambassador to Britain under President Richard Nixon, died in 2002.

The big diamond combines the best of the four C’s: top colour, perfect clarity, ideal cut and excellent weight.

Annenberg purchased the ring for herself to mark her 90th birthday, Christie’s said. It was delivered by armed guards to her Rancho Mirage, Calif., home from the Beverly Hills jeweler’s store, it said. She was thrilled whenever someone came by to admire it, the auction house said.

The ring’s pre-sale estimate was $3 million to $5 million. The previous auction record for a 30-carat square cut flawless, colourless diamond was $3.1 million, set at Christie’s in Geneva in May.

The record for any diamond or jewel at auction is $24.3 million for the 17th century cushion-shaped grayish-blue 35.56 carat Wittelsbach Diamond.