The brooch is in the shape of a scroll set with pink topaz and diamonds and has an oval pink drop topaz.
The royal brooch has an interesting history. It originally belonged to Augusta Duchess of Cambridge and then to her daughter, also Augusta, who was Grand Duchess of Mecklenburg Strelitz.
It became the property of Queen Mary who was particularly fond of pastel-coloured stones and admired the delicate color of the pink topaz in the brooch.
According to a news report, she presented it to Lady Alice Montagu-Douglas-Scott, before her wedding in 1935 to her son the Duke of Gloucester.
The Duchess of Gloucester lent this unusual pink topaz brooch, one of her favourite pieces of jewellery, to an exhibition at the Cafe Royal on 5-6 July 1956 in London. The "Jewel Luncheon and Exhibition" was a fundraiser for the Gosfield Hall, a residential nursing home for the elderly. The Duchess opened the exhibition.
The ladies attending the luncheons were asked to wear their favourite pieces of jewellery. Eight leading London jewellers participated in the exhibition showing antique eighteenth-century diamond jewels and modern jewellery.
Later Duchess Alice, presented the brooch to her daughter-in-law Brigitte Duchess of Gloucester, who wore it in public at a gala event.
Above on the left, Princess Augusta 1797-1889, third daughter of Friedrich III, Landgrave of Hesse-Cassel.
In 1818 she married her second cousin, Adolphus, Duke of Cambridge. They lived in Hanover, where the Duke held the post of Viceroy, until the ascension of Queen Victoria and the separation of the Hanoverian and British crowns.
Upon their return to Britain in 1837, they lived at Cambridge Cottage, Kew, and later at St. James' Palace.
They had three children; George, second Duke of Cambridge, Princess Augusta later Duchess of Mecklenburg-Strelitz, and Princess Mary Adelaide of Cambridge, later Duchess of Teck.
More topaz jewels were presented by Queen Mary to the Duchess of Gloucester probably in 1953:
Bangle/bracelet with large oval topaz
Brooch of topaz with diamonds with large pedant of an pear-shaped topaz and diamonds, a bow of diamonds between.
Brooch with oval topaz and diamonds, fitting the center of the Greek honeysuckle-pattern tiara, with rising centre, worn by Queen Mary from at least 1939 and later.
Oval topaz with border of diamonds, worn as pendant of the Duchesses of Gloucester.
Sources: The Age (Melbourne, Australia)