The Duke and Duchess of Cornwall of York (later King George V and Queen Mary) toured the Commonwealth for six months March to October 1901, visiting Gibraltar, Malta, Aden, Ceylon, Singapore, Australia, New Zealand, Mauritius, Natal and Cape of Good Hope, and Canada.
The highlight of the tour was the opening of the first Australian Federal Parliament in Melbourne 9 May 1901. On the evening after the formal opening there was a gala reception, and the dress of the duchess was described thus in The London Times: ´The Duchess of Cornwall, who was dressed in black, wore a tiara and a necklace of amethysts, which belonged to Queen Charlotte´.
The royals were still in mourning for Queen Victoria, who had died the previous January, which explain the sombre colour of the dress and the appropriate amethyst jewels.
I wonder, however, if you have previously read of an amethyst tiara (or other amethyst jewels) from Queen Charlotte? There are not many amethyst jewels in use today except the Kent demi-parure. There was an amethyst tiara which belonged to Queen Mary and was later sold by a descendant (sometimes wrongly described as sold by the late Queen Mother). Others?