Lechuguilla Cave | Planet Earth

The walls of these caves are covered in fragile crystals made of gypsum, which is created when limestone is dissolved by sulphuric acid.

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Sussex gypsum mining | The Great British Countryside

Hugh Dennis visits a gypsum mine under the Sussex Weald.
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Stalactites and stalagmites | Planet Earth

How stalactites and stalagmites are formed in caves, from limestone dissolved in water droplets.