J.C. REVY, ISM / SCIENCE PHOTO LIBRARY J.C. REVY, ISM / SCIENCE PHOTO LIBRARY
A mineral formation known as a septarian concretion, photographed in ultraviolet light. The mineral has been sectioned and polished to show its internal structure. Septarian concretions display mineralised, irregular, polygonal joints or cracks (seen within the grey outer layer here). The structure resembles the pattern of cracks which develops in dried mud, and probably results from a similar desiccation process. Compare with photo E425/499 which shows the same specimen in normal light.
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