Answer:
The Arkenstone
Explanation:
The Arkenstone symbolizes a bygone era of peace—a time when Thorin's ancestors were at one with nature and the species of Middle-earth lived in harmony. Thorin is desperate to keep the Arkenstone (and the rest of his treasure hoard), refusing to share it with anyone. Thorin is buried with the Arkenstone, which symbolizes his return to his people as well as the loss of peace in Middle-earth—symbolic foreshadowing of the adventurous trilogy to come.