ADAM HART-DAVIS / SCIENCE PHOTO LIBRARY ADAM HART-DAVIS / SCIENCE PHOTO LIBRARY
Monoclinic sulphur from solfataras (volcanic vents in the ground). These vents are usually an inch or two across and they emit steam, sulphur dioxide, hydrogen sulphide and elemental sulphur. Sublimation of the vapour as it cools in the air outside produces crystals like these, seen at Sulphur Banks, just outside the main caldera of Kilauea volcano in Hawaii.
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