Где упоминается мифрил:

HoME 7-2. Неустановленное "тайное оружие" Саурона.

'Mithril is now nearly all lost. Orcs plunder it and pay tribute to  Sauron who is collecting it -  we don't know why - for   some secret purpose of his weapons  not for beauty.'
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Hobbit. Кольчуга Бильбо.

With that he put on Bilbo a small coat of mail, wrought
for some young elf-prince long ago. It was of silver-steel which the elves call mithril, and with it went a belt of pearls and crystals.
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UT. Элендилмир.

Next to it lay a treasure without price, long mourned as lost for ever: the Elendilmir itself, the white star of Elvish crystal upon a fillet of mithril that had descended from Silmarien to Elendil, and had been taken by him as the token of royalty in the North Kingdom.
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LotR

1. Корабль Эарендила

A ship then new they built for him
of mithril and of elven-glass
with shining prow; no shaven oar
nor sail she bore on silver mast:
the Silmaril as lantern light
and banner bright with living flame
to gleam thereon by Elbereth
herself was set, who thither came
and wings immortal made for him,
and laid on him undying doom,
to sail the shoreless skies and come
behind the Sun and light of Moon.

2. Митрильная кольчуга Бильбо; итильдин эльфийских мастеров.

`Mithril! All folk desired it. It could be beaten like copper, and polished like glass; and the Dwarves could make of it a metal, light and yet harder than tempered steel. Its beauty was like to that of common silver, but the beauty of mithril did not tarnish or grow dim. The Elves dearly loved it, and among many uses they made of it ithildin, starmoon, which you saw upon the doors. Bilbo had a corslet of mithril-rings that Thorin gave him.
'

3. Шлемы Стражей
The Guards of the gate were robed in black, and the
ir helms were of strange shape, high-crowned, with long cheek-guards close-fitting to the face, and above the cheek-guards were set the white wings of sea-birds
; but the helms gleamed with a flame of silver, for they were indeed wrought of mithril, heirlooms from the glory of old days.

4. Вышивка на знамени - вероятно, митрильная нить.
There flowered a White Tree, and that was for Gondor; but Seven Stars were about it, and a high crown above it, the signs of Elendil that no lord had borne for years beyond count.
And the stars flamed in the sunlight, for they were wrought of gems by Arwen daughter of Elrond; and the crown was bright in the morning, for it was wrought of
mithril and gold.

5. Ворота Гондора.
In his time the City was made more fair than it had ever been, even in the days of its first glory; and it was filled with trees and with fountains, and its gates were wrought of mithril and steel, and its streets were paved with white marble;

6. Нэнья.
On her finger was Nenya, the ring wrought of
mithril, that bore a single white stone flickering like a frosty star.
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HoME 6-4, кольчуга Бильбо

This   passage   was   changed   in   the   act   of    writing   from:
-  very  abundantly  in the  earlier days,  and especially  the silver. Moria-silver  was  (and  still  is)  renowned;  and  many  held   it  a  precious
This is where the conception of mithril first  emerged, though  not yet the  name  (see  note  34).  The  reference  to  mithril in  The Hobbit (Chapter XIII, 'Not at  Home') entered  in the  third edition  of 1966: until then the text  read: 'It  was of  silvered steel,  and ornamented       with pearls, and with it went a belt of pearls and crystals.'  This was changed to: 'It was of silver-steel, which the elves call  mithril, and with it went a belt of pearls and crystals.'

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HoME 7-1. habergeon, чем бы он ни был

In panoply of Elven-kings,
in silver rings they armoured him;
his shield they writ with elven-runes
that never wound did harm to him.         56
His bow was made of dragon-horn,

his arrows shorn of ebony,
of mithril was his habergeon,
his scabbard of chalcedony.

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HoME 9-1. Кольца, подаренные Фродо после победы.

But Gandalf came and with him went an esquire, no more than a small lad he seemed, though clad in the silver and sable of the king's guard, and to the wonder of Frodo and  Sam they bore the sword and the elven-cloak and the   mithril-coat  that had been taken from them; and for Sam  they brought a coat of gilded mail, and on Frodo's right   hand upon the middle (9) and little fingers they set small rings of mithril set each with a gem like a star.

Ещё один вариант  того же самого:

...  and on Frodo's right hand, upon the middle and little fingers, he set fine rings of mithril, slender as threads of  silk but bearing each a small gem shining like a star.
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Другие названия митрила (позже отвергнутые)  - ithil, thilevril, erceleb.
Другие названия итильдина - starmoon, thilevril.

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