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"The Marble Index," Nico's sophomore album, stands as a seminal work of experimental music. Produced by the avant-garde composer John Cale, the album is characterized by its sparse, hypnotic soundscapes and Nico's haunting vocals. Notably departing from her earlier collaboration with The Velvet Underground, "The Marble Index" solidified Nico's position as a unique and influential artist in her own right.