It seems that Camilla, Duchess of Cornwall, wore this bracelet a few days ago, when she attended, with the Prince of Wales, a private dinner in Washington, DC, at Barby Allbritton's home (Mrs Allbritton is the chairwoman of the Prince of Wales' U.S. Foundation):
(Source: Chris Jackson/Getty Images North America)
And here is a good HQ pic:
Judging from the colour and chatoyancy of the central stone, I would guess it could be a variety of tiger's eye, or cat's eye. What do you think?