A very unusual lab-created gemstone, chromium-doped Laser YAG (Yttrium Aluminium Garnet) has an extraordinary optical property.

It's colour is utterly unique and hard to capture in still photos or on video, depending heavily on the light in which the stone is viewed.
It is predominantly a deep tsavorite-like forest-green colour, but the addition of Chromium gives the stone an extremely strong red fluorescence which is visible in daylight.
This leads to a combination of green and orange-red colours playing through the gem as it is tilted in the light and gives this unique YAG variety its commercial name, "Christmas Garnet".

Images 1 and 5 were taken in household LED light and daylight-approximate lighting.
My images do not do the gem any justice, it is a far more captivating display in the hand, different viewing angles showing shifting colours, unlike anything found in nature!
Image 5 shows the extreme red fluorescence using a standard UV penlight.

weight:  5.16 carats
shape:   Oval cut
dimensions:   11.52 x 8.49 x 6.00 mm
treatment:  Not applicable