The Mirror of Great Britain was a piece of jewellery that was part of the Crown Jewels of the United Kingdom during the reign of James I of England and VI of Scotland.
The jewel was created around 1604 to mark James's Union of the Crowns of England and Scotland. It was created in gold with five main stones set into it: four diamonds and a ruby. The ruby and one of the diamonds were table-cut, while two further diamonds were lozenges. One of them was known as the "Stone of the letter H of Scotland" or the "Great Harry" and had belonged to James's mother, Mary, Queen of Scots. The final diamond was the Sancy Diamond which is believed to have been previously owned by the Burgundian crown. The jewel was also decorated with two pearls and a number of smaller diamonds.
The diamond used in the piece from the "Great Harry" appears to have been a gift to Mary, Queen of Scots from Henry II of France.
In 1625, James pawned the jewel, and it was split up. The pearls remained in royal possession for another year but were then also pawned. The Sancy Diamond was reclaimed but again pawned in 1654 and subsequently became part of the French Crown Jewels. The Sancy Diamond is now in the collection at the Louvre.
The National Galleries of Scotland collection includes a 1604 portrait by John de Critz of James I and VI wearing the Mirror of Great Britain on his hat.