The Elendilmir, "jewel
of Elendil",
was a gem called the Star of Elendil. It was a
single white gem worn on the brow, held by a silver
fillet (narrow headband), used by the Kings of Arnor who wore no crown.
Rather than this fillet, the Sceptre of Annúminas was the chief mark of
royalty in Numenor and Arnor. It was one of the heirlooms of the house
of the High King kept safely in Imladris (Rivendell): "the ring of
Barahir, the shards of Narsil, the star of Elendil, and the sceptre of Annúminas."
References:
Return of the King: Appendix A: note following the
death of Last King Arvedui and in the text above listing heirlooms. Merriam Webster's Collegiate Dictonary 10th edition.
More information is given in the Unfinished Tales, "Disaster of the Gladden Fields".
After the fall of Sauron, Isildur returned to
Gondor, assumed the Elendilmir, and proclaimed himself the High King of
Arnor and Gondor. He stayed in Gondor a year, restoring order and
defining boundaries while most of the army returned to Eriador. After
that year he left in haste to go to Imladris where he had left his wife
and youngest son, Valandil, and greatly wished the counsel of Elrond.
With a party of warriors and two of his sons, Elendur and Ciryon, Isildur took the faster road. Since
his party had no horses fit for riding, he figured forty days of travel
to arrive before winter. Sauron was vanquished and he was passing
through country held by allies, so his people were not as vigilant as
they might have been. Going around the rain-swollen Anduin, Isildur's
party used paths of the Silvan elves of Mirkwood, and from that wood
were attacked by a party including great orcs as well as normal orcs,
for the Ring called the orcs to itself for aid. Isildur, seeing that
his people were outnumbered and in a bad position, gave some of his
heirlooms to "Ohtar", a formal title he used for his esquire who was a
kinsman, and commanded him to take the heirlooms to safety in Imladris
with the help of his own companion, and they were overheard by one who
would be the only other survivor, Estelmo, Elendur's esquire. Ohtar,
however, carried only the shards of Narsil and its great sheath. The
orcs avoided Isildur for fear of the Elendilmir that he wore.
When all
was seen to be lost, Isildur took Elendur's counsel to take the One
Ring away from potential capture by using the invisibility it could
confer, despite the pain of putting it on; so he had to take it from
the gold case, called a wallet, that was on a chain around his neck.
The Elendilmir, however, could not be quenched, and wearing the One
Ring made the Elendilmir of the West blaze up wrathfully in red,
causing both Men and Orcs to back away in fear. Isildur had to cover
the jewel with his hood to vanish. To swim the Anduin, he removed his
armor and weapons except for a short sword. Later, men found on that
bank his mail, helm, shield and greatsword but nothing else. He
traveled the stream to the Gladden Fields, but on the way the One Ring
slipped from his finger to be much later discovered by the hobbit,
Deagol, near the edge of the Gladden Fields close to the western bank.
When Isildur rose up on shore, the night-eyed orcs saw him as a
"monstrous shadow of fear, with a piercing eye like a star". He
fell, riddled with arrows, in shallow water, no more than shoulder-high. His body was not
seen again by Elves or Men.
A new Elendilmir was made for Valandil to wear and
passed down all the way to Aragorn II. It was a jewel of great beauty
fashioned by Elven-smiths in Imladris for Valandil, and was worn by
thirty-eight heads before it came to Aragorn II.
After Aragorn II had become High King, he began
re-ordering Gondor. One of his first tasks was the restoration of
Orthanc, in which they discovered many stolen treasures. Only Gimli was
able to find and open the hidden door behind which was a steel closet.
It held the gold case and chain that had once contained the One Ring
and by it was the Elendilmir. This original version was a white star of Elvish crystal
upon a fillet of mithril that had come from Silmarien to Elendil and
that Elendil had used as a token of royalty in the North Kingdom, more
ancient and potent than the one in use at that time. Aragorn kept the ancient
Elendilmir safely hidden, wearing it only on high days in the North
Kingdom after the first time, when Arwen put it on him after he went to
the North and took up the full kingship of Arnor, and it gave off its
splendor. [Unfinished Tales, "The Disaster of the Gladden Fields", chapter and notes.]
According to Appendix B, in The Tale of Years in The Return of the King, in year 16 of the Fourth Age, Aragorn gave the Star of the Dúnedain
to Master Samwise Gamgee, Mayor of the Shire, and once a Ring-bearer.
This would have to be the second Elendilmir, rather than the hidden
first one.
Other names for the Elendilmir were the Star of Elendil, Star of the Dúnedain, Star of the North, and the Star of the North-kingdom.
The Elendilmir is not to be confused with the Elendil Stone, which was the palantír of Emyn Beraid that looked only to the Sea with straight sight. This stone and tower were guarded and maintained by Círdan
and the elves of Lindon. It apparently could see all the way to the
Tower of Avallone on Eressea where the Master-stone remained. [UT "The Palantíri" note 16, p. 432.]