The Elessar, at least the original one made in Gondolin that trapped sunlight in it and was said to enable people looking through it to see the old as young again and also to heal.
I doubt the first part can be really explained by science but what about the second part?
Do solar rays have healing powers?
Can a gem refract the light in such a way to make this possible?
No idea, maybe you can think of something.
