Sun Stone

"That's the Sun Keep you see on the southern continent. A Sun Stone, once the source of this world's power, was kept there. But when we began using our new energy source, it was sealed up just like the north palace. They claim we don't need the energy of this tired, old planet."

- Young Man in Kajar

The  is a Key Item in. The stone requires constant exposure to sunlight for several million years before storing enough to generate power. When the stone dims from use or lack of sunlight, it is known as Moon Stone. Able to store solar energy within its spherical surface, it releases beams of light when struck, as demonstrated by Taban during the Moonlight Parade in Leene Square. In an optional quest, this item is obtained by leaving the Moon Stone in the Sun Shrine from Prehistory to the Future.

History
Stored in a Palace of Zeal, this brightly colored rock previously fueled the floating islands of the Kingdom prior to the invention of the Mammon Machine. Serving as the foremost source of elemental energy for the sorcerers of Zeal, the Sun Stone is used to craft powerful defensive armors such as Red Plate and Blue Vest, and powerful weapons, such as the Swallow. It is apparent that the people of Zeal once owed their well-being to the planet and her natural gifts; however, with the advent of the Mammon Machine, elemental energy usage was forbidden and the items created with it were sealed in the North Palace. After 65000000 years, the Sun Stone dims, leading to such statements as "we do not need the energy of this tired, old planet," from the citizens of Enhasa and Kajar. Technologies such as the Land Bridges and Skyways were fueled by the stone, and what appear to be Dreamstone glyphs. After defeating the Son of the Sun in the Sun Temple, Crono and his friends store it in the Sun Shrine, northeast of the Tyranno Lair in Prehistory. The time-travelers hop through time to check on the rock's progress.

During the Present, the Porre Mayor steals the stone from the Sun Shrine. Half-charged, Crono locates the relic from the rays of sparkling light emitting from the Manor in Porre. The selfish man lies about stealing the stone and refuses to hand it over. Traveling backwards in time to convince his ancestors to instill honesty in their children, Crono returns to the Porre Mayor, now a generous man, and receives the stone. Spiced Jerky is necessary for completing this task. If Crono already gave the man's ancestor the Jerky, he will already be generous and will simply hand over the stone when questioned.

Bringing the stone to Lucca's House, if Lucca is not present when the stone is plucked from the Pedestal in the Future, she creates the Wondershot (her best gun) from it. Her father, Taban, creates the Sunglasses, as well. If the Rainbow Shell is recovered from Giant's Claw and transported to Guardia Castle, Melchior creates Rainbow (Crono's best katana) and PrismSpecs (an accessory that maximizes attack) from an alloy of the shell and the stone. During the Moonlight Parade, Taban strikes the stone with a mallet to produce fireworks for the festival-goers.

Chrono Cross
Since Taban retains the stone in the ending of Chrono Trigger, it can be inferred that he still possesses it long after Lavos is destroyed. Because Lucca opens an orphanage in the same location, and lives with Taban and her mother, it is assumed agents from Porre stole the stone while burning the home in search of the Prometheus Circuit.