The Heartstone is a giant luminous gem which is the life force for all of Troll kind. It has healing powers, so they take the wounded or sick to the Heartstone for treatment. The most common one is located in the center of Heartstone Trollmarket, underneath Arcadia Oaks.
After Gunmar and his Gumm-Gumm Army were banished to the Darklands, some trolls traveled to America aboard the Mayflower and eventually found a new Heartstone underneath what would be known as Arcadia Oaks, from which they built Trollmarket underneath around the new Heartstone.
Barbara Lake was wounded and taken to the Heartstone, prior to the loss of all memories made between the joining of herself and Stricklander’s fates and the present. This includes all memories of trolls.
When Gunmar took over Trollmarket, he was also granted access to the Heartstone, enabling him to drain its energy to regain his former strength, causing the gigantic crystal to turn black as did the first Heartstone that spawned the Skullcrusher.
When Gunmar managed to retrieve the Staff of Avalon, it is revealed that Morgana was imprisoned in a secret chamber underneath the Heartstone. Gunmar tried to free her but Merlin had a safeguard in his staff that would only allow human hands to recite the trollish incantation. Usurna later captured Stricklander and Barbara, the latter threatened by Gunmar to force the former to use the staff. Stricklander managed to purposely let the Staff's energies run wild, allowing him and Barbara to flee, forcing Gunmar to steer the energies towards Morgana's prison, freeing the Eldritch Queen.
In unleashing the Eternal Night, Morgana's spell destroyed the Heartstone, rendering Trollmarket uninhabitable. After the Eternal Night war, Jim and the other trolls venture to New Jersey in search of a new Heartstone.
The Heartstone is a source of life and sustenance. It has the power to sustain life force to all trollkind, preventing them from crumbling to stone. It can also heal the sick and the injured.
- According to Welcome to the Darklands, there are Heartstones within the Darklands. Gunmar’s throne is actually carved from one. This would make sense because it’s the Trolls original homeworld, but because the dark realm is decaying from both Gunmar's corruption and the Earth's mantle, all the realm's Heartstones are dying, making their power insufficient.