National Geographic : 1951 Nov
© National Geographic Society 647 Ektachromes by Willard R. Culver Birthplaces of These Minerals Range from Earth's Surface to a Mile or More Deep Their age varies from a few centuries to nearly a billion years. Sulfur crystals (upper left) solidified from gases in a Chilean volcano's crater in comparatively recent times. Crystals of wulfenite (upper right) were formed several hundred feet below the surface. Rhodonite (lower left), a manganese silicate, created thousands of feet down under great heat and pressure about 800 million years ago, was brought to the surface by upheavals and erosion. Lower right: Malachite from Tsumeb, South-West Africa.