A small, star-colored talisman.
The Astral Amulet is an enigmatic pouch with a wooden pendant inside carried by Kid. Its origins and nature are unclear; the pendant was probably created by Lucca soon after Kid came to live with her. The purple pouch bears the Zeal royal crest in black and gold. Kid presumably had the Astral Amulet when Lucca's house burned to the ground. In 1020 A.D., after Kid and Serge first met, they were told by Direa that the amulet possessed an extraordinary power that could unlock doors to other worlds. After Kid had been poisoned, she instructed Serge to use it to go between Home World and Another World at will (and depending on events, he kept it or Korcha made him leave it at her side). The amulet was successfully used to this end until Serge's body transformed to that of Lynx; it then stopped responding to Angelus Errare. After the Dead Sea was dissolved, it functioned regularly until the end of Serge's quest and the Unification of Dimensions. How it was imbued with the ability to enable Serge's constant crossing the dimensions is unknown. While Schala's Pendant seems as if it can be construed as the object inside the pouch, remember that it was made out of Dreamstone, not wood. Similarly, Kid's incomplete Time Egg also appears (from the complete Key Item picture) to be made out of magical, perhaps composite materials, suggesting it is a different item apart from the amulet and Pendant as well.
Theory and Analysis
From: Key Items (Chrono Cross)