Well, sort of - it's a diamond lit by a green laser, a ring I inherited from my father many years ago. I shot this for a photo community on livejournal that sets topics once a week, this week was "diamond".
Nikon D90, 50mm lens, 36mm extension tube, green laser illumination, also some daylight and LED room light. 1/160th f11. Important safety hint - I used the liveview feature of the camera for this one so that I was not staring at a laser for extended periods, that's really not a good idea!
The monochromatic light looks a little odd, but it's fairly typical of laser lighting, it tends to drown out minor variations in shade.
What I actually wanted to do was use a UV laser, since diamonds fluoresce slightly, but it's gone missing since I last used it.