The Gemini Coin is a coin that is a part of the Voice of the Night Sky quest and is needed to complete the Signs of the Zodiac subquest. You can find this coin in the zoom-mode spot located in Silent Cavern, which requires a dolphin partner to unlock. Along with the coin are some some Starck's Demoiselles. This coin is engraved with the constellation Gemini, one of the twelve signs of the zodiac, represented by twins.