Rainbow Shell (Origin of)
Huge Nautiliuses existed in prehistory, though the Ice Age resulted in their extinction. Nonetheless, a certain shell was held by the Reptites in the Tyrano Lair. When Lavos impacted the planet, the high pressure and temperature of his contact compressed and enriched the shell.
The Rainbow Shell is regular material imbued with concentrated magic. When Lavos impacted the planet, Lavos emanated magic energy while spinning from his meteoric trek; this ground the material into a spiral shape and also gave it magic. The Shiny material of Chrono Cross could be considered similar to this effect.
From: Theory (Objects)