EDIT: Thanks to Jay Pasachoff for correcting me -- it's the Sun's photosphere, not corona, that makes the brilliant diamond on the ring.
And thanks to Daniel Fischer for pointing out this video sequence of the Earthrise, of which the image I show below is a still. Cool!
JAXA and NHK just released this lovely shot of an Earthrise taken by Kaguya during a penumbral lunar eclipse, when Earth blotted out almost all the light from the Sun except for one tiny edge of the Sun's disk. The sunlight peeking over the edge of the disk at about 4:00 makes the brilliant "gem" on the "diamond ring" -- the ring is, I believe, Earth's atmosphere, scattering sunlight forward to the camera.