Stalactites and stalagmites in the Grail's Castle section of the Fairy Caves in Saalfeld, southeastern Germany, had a spring cleaning this week. The caves are renowned as the most colourful in the world, a result of the unusual composition of the encrusting rocks. Most stalactites are formed of calcium carbonate and similar minerals: Saalfeld's are iron phosphate.
In geological terms, these speleothems are youngsters: they have formed only 90 years ago. The cave system originated as mines for the mineral alum between 1543 and 1846. In 1910, the caves were flooded and the stalactites and stalagmites began to form as water carrying dissolved minerals seeped through the rocks. Now the caves are known as the most beautiful in Germany.
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