APA
Walter Schumann, . (1976). Gemstones of the world. Sterling, New York: .
Chicago
Walter Schumann, . 1976. Gemstones of the world. Sterling, New York: .
Harvard
Walter Schumann, . (1976). Gemstones of the world. Sterling, New York: .
MLA
Walter Schumann, . Gemstones of the world. Sterling, New York: . 1976.