- "It was a globe with a thousand facets; it shone like silver in the firelight, like water in the sun, like snow under the stars, like rain upon the Moon!"
- —Thorin Oakenshield 
The Arkenstone was a wondrous gem sought by Thorin Oakenshield which had been discovered beneath the Lonely Mountain by Thorin's grandfather Thrór, and then shaped by the Dwarves. The Arkenstone had been the family heirloom of Durin's folk, but was lost when the dragon Smaug stole the mountain from the Dwarves.
The Arkenstone shone of its own inner light, and appeared a "little globe of pallid light" in darkness, and yet, cut and fashioned by the Dwarves, it took all light that fell upon it and changed it into "ten thousand sparks of white radiance, shot with glints of the rainbow".
The Arkenstone was a gem, the object most prized by Thorin Oakenshield of all the treasures of the Lonely Mountain. Such did he consider its value that he was willing to trade 1/14th of all the gold and silver of Smaug's hoard for it.
When Bilbo Baggins found it on Smaug's golden bed deep inside the Lonely Mountain, he pocketed it, having learned how much Thorin valued it. While the Dwarves with Thorin sorted the treasure, Thorin sought only the Arkenstone, unaware that Bilbo was hiding it in his pillow. When the Dwarves refused to share any of the treasure with King Thranduil and Bard, the man who had killed Smaug the Magnificent, Bilbo crept out of the Dwarves' fort inside the Mountain, and gave them the Arkenstone; Bard, Thranduil, and Gandalf then tried to trade it for Bilbo's fourteenth share of Smaug's hoard. Then an army of Orcs arriving from the Grey Mountains interrupted the dispute, the Battle of the Five Armies ensued, and Thorin was killed. The Arkenstone was placed upon Thorin's chest within his tomb deep under the Lonely Mountain, and so was returned to the earth at last.
The name Arkenstone may have been related to the Gothic word aírkns ("holy"). More closely related may be Old English eorcnanstan ("precious stone") and Old Norse jarknasteinn.
- The Arkenstone does not appear in the 1977 Rankin/Bass animated The Hobbit adaptation. As a result, Thorin loses respect for Bilbo out of feeling that the Hobbit will never understand honour and war.
|Foreign Language||Translated name|
|Chinese (Hong Kong)||家傳寶鑽|
|Portuguese (Brazil)||Pedra Arken|
|Spanish (Spain and Latin America)||Piedra del Arca|