Hand touching the giant gypsum crystals inside the Pulpi Geode. The geode is one of the largest discovered, eight metres long inside and nearly two metres wide. It is lined with huge crystals of gypsum (calcium sulphate), which crystallised from a hot saturated solution over thousands of years. It was discovered in 1999 in an abandoned iron, lead and silver mine, the Quien Tal Pensara Mine, in Almeria, Spain.