Warning! Potential spoilers ahead.
“During preproduction for Star Wars: The Last Jedi I heard rumors about Luke Skywalker having a Kyber crystal he was protecting and/or hiding. One version of the story basically went that Skywalker appeared to have pieces of Darth Vader’s lightsaber on him but they were obscured and you wouldn’t really notice unless you were into the lore. Those kinds of rumors are always fun, especially when they’re coming from credible avenues of information.
I have been told that in Star Wars: The Last Jedi our favorite Skywalker is wearing a pretty cool necklace that might connect to that rumor. The shape supposedly is sort of like that of a wooden dog whistle when seen from a distance. I know that’s a weird analogy but that’s what I was told. However, the interesting part is that when you look at the bottom of the necklace hanging around the neck of Luke Skywalker, you will see a red crystal protruding from the bottom of it.
The red crystal or gem on the bottom of the necklace is factual and very solid information and he does wear it in the film. I don’t know if this is a story element explored in the film or if it will just be a part of the lore. […]”
Read more at MakingStarWars.net.