- "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 or Heart of the Mountain was a wondrous gem sought by Thorin Oakenshield which had been discovered beneath the Lonely Mountain during the reign of Thráin I, and then shaped by the Dwarves. The Arkenstone became the family heirloom of the Kings 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 discovered not longer after the founding of the Dwarf kingdom under the mountain by Thráin I. After it's discovery and cutting by Dwarf artisans the jewel became an heirloom of the Kings of Durin's Folk and was taken by Thorin I to the Grey Mountains when he removed his people there. The Arkenstone returned to the Lonely Mountain centuries later, returned by King Thrór after Dragons drove his people out of the Grey Mountains. When Smaug came to the Lonely Mountain the Arkenstone became a part of his hoard.
The gem was 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, 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.
Portrayal in Adaptations
In Peter Jackson's Hobbit trilogy the Arkenstone is discovered during the reign of Thrór, not Thráin I and feeds into the growing greed of Thorin's grandfather. In the books this greed is partly caused by possessing one of the Seven Rings of Power, but in the films it is the Arkenstone itself that causes 'Dragon sickness'. In addition possession of the Arkenstone grants the holder the right to summon the seven armies of the Dwarves, an inherent contradiction given that Thrór does not possess it at the time of the Battle of Azanulbizar.
|Foreign Language||Translated name|
|Chinese (Hong Kong)||家傳寶鑽|
|Portuguese (Brazil)||Pedra Arken|
|Spanish (Spain and Latin America)||Piedra del Arca|
- The Hobbit, Chapter XII: "Inside Information"
- The Hobbit, Chapter XIII: "Not at Home"
- The Hobbit, Chapter XVI, "A Thief in the Night"
- The Hobbit, Chapter XVIII, "The Return Journey"
- The History of Middle-earth, Vol. IV: The Shaping of Middle-earth, chapter VI: "The Earliest Annals of Valinor"
- Peter Gilliver, J. Marshall, E. Weiner, The Ring of Words, III. Word Studies, "Arkenstone"