Silmaril

The ultimate in shiny, these gems were made by Fëanor with living light from Laurelin and Telperion, the Two Trees of Valinor. They were then nicked by Morgoth, which caused Fëanor to go more than slightly off his head and to subsequently precipitate a huge string of nastiness that included the Kinslaying and the Sinking of Beleriand (the latter somewhat indirectly).

One Silmaril was stolen back from Morgoth by Beren and Lúthien Tinúviel, and was eventually given to the Valar by Eärendil as a token of repentance on the part of the Noldor as a whole. This Silmaril was set in the sky as a star. The other two eventually came into the hands of Maedhros and Maglor, two of Fëanor's sons, and at the end of the day wound up in a fiery pit and at the bottom of the sea respectively. Thus all three elements of Arda- sky, fire, and water- were represented, as Elrond will be certain to point out in his Numerology 101 class.

There were always three Silmarils, and the presence of any more is a definite sign of worry for a PPC Agent on the job. Since the Silmarils indelibly burn pretty much anyone who touches them thanks to the oath sworn by Fëanor and his sons, handling them is nigh-on impossible even if they're one that's not supposed to properly exist. Silmarils, of course, are high on the list of items that are Absolutely Forbidden to be taken into possession of PPC Agents.