For the composer of electronic and new age music, see David Arkenstone.
The Arkenstone (or "Heart of the Mountain") of Thráin was a wondrous large white gem sought by Thorin Oakenshield in J. R. R. Tolkien's The Hobbit. It was discovered beneath Erebor (the Lonely Mountain) by Thorin's ancestor Thráin and shaped by the Dwarves. The Arkenstone became the family heirloom of Durin's folk, but was lost when the dragon Smaug captured the mountain from the Dwarves (in the year 2770 of the Third Age). The Arkenstone shone of its own inner light, but having been cut and fashioned by the Dwarves, it also reflected and multiplied any light glancing upon its surface with marvellous beauty.The Arkenstone resembles the Silmarils in some respects, though it is not one.When Bilbo Baggins found it on Smaug's golden bed deep inside the Lonely Mountain (year 2941 of the Third Age), he pocketed it, having learned how much Thorin valued it. While the Dwarves with Thorin sorted the treasure, Thorin