In the 1960s Gerhard (a Catalan who left Spain for exile after the Franco side's victory in the Spanish Civil War and made his career in Britain), wrote this composition as part of a group of works collectively called the Astrological Series. (The others in the group are Libra and Leo. It is a searching fifteen-minute one-movement piece in Gerhard's personal version of the twelve-tone system. It begins with the two instruments in harsh confrontation. Musically hammering at each other, they seem to come to an understanding as the music becomes progressively more melodic.
Some commentators have seen Gemini as the middle point or keystone of the Astrological Series. This particular piece also refers to the American space program named "Gemini" and reflects Gerhard's deep fascination in the opening stages of the exploration of outer space.