A dazzling tiara worn at two British coronations and the Star of Egypt diamond purportedly once belonging to King Farouk are among the historic jewellery items being auctioned Wednesday by Christie's in Geneva.

The glittering pieces are going under the hammer in the auction house's Magnificent Jewels sale in the Swiss city.

The sale also features the largest private collection of JAR jewellery ever to come to auction, spanning 40 years of the work of Paris-based creator Joel Arthur Rosenthal.

Less than a fortnight after the coronation of Britain's King Charles III comes the sale of the Bessborough Diamond Tiara, which was worn at the coronations of his grandfather King George VI in 1937 and mother Queen Elizabeth II in 1953.

Vere Ponsonby, the ninth earl of Bessborough, commissioned the Parisian jeweller Chaumet to craft a tiara for his wife to mark his appointment as Canada's governor-general in 1931.

The Art Deco tiara, made with platinum and weighing 136.5 grams, has an intricate floral design.

"This is as iconic as it gets in terms of the style. The workmanship is unbelievable," said Max Fawcett, head of the jewellery department at Christie's in Geneva.

"This is quite crown-like, which is fitting for this year as it has been through two coronations," he told AFP.

"It's a piece of art and a piece of history."

It is expected to fetch between 800,000 and 1.5 million Swiss francs ($890,000-$1.67 million).

- Star of Egypt -

The Star of Egypt is a spectacular unmounted 105.52-carat diamond.

Its origins are shrouded in mystery and it was reportedly bought in 1850 by the viceroy of Egypt, who sold it in 1880.

It first appeared on the London market in 1939.

It was seemingly later bought by King Farouk, who ruled Egypt from 1936 to 1952. His impressive jewellery collection vanished when he fled into exile, and only reappeared several years later. The Star of Egypt was bought alongside jewels known to be in his possession.

It has been in the same family since the 1970s and has never been auctioned before.

It is estimated at two to three million Swiss francs.

"The shape of it is incredible, the square emerald cut. It's an absolutely gorgeous stone," said Fawcett.

- JARs on the shelf -

The 28 lots by Joel Arthur Rosenthal (JAR) were amassed by a single collector over 15 years.

Rosenthal, who was born in New York but moved to Paris, produces up to 70 meticulously-crafted pieces a year.

These are mostly pre-assigned to his existing collectors and friends, "so as a new collector it's difficult to get in there", Rahul Kadakia, Christie's international head of jewellery, told AFP.

"What's nice is that there are lots priced from 3,000 to 400,000 (Swiss francs), so there's a jewel or object for every level of collector."

The most eye-catching is the 2011 sapphire, spinel and diamond 'eye' bangle, estimated at 150,000-200,000 Swiss francs. Its blue iris and black pupil is set on a golden expandable bracelet.

"JAR is super-creative and inventive in the way he uses gemstones and fuses colours together," said Kadakia.

"It's so realistic. Even when you look in profile it shows you the curve of the eyeball."

The priciest of the 102 lots is a Cartier Belle Epoque natural pearl and diamond devant-de-corsage formerly owned by Australian opera singer Nellie Melba.

It was made in around 1902 and is estimated to be worth 2.5 to 3.5 million Swiss francs.