Crystal Caves references https://slideplayer.com/slide/5933049/ https://www.housebeautiful.com/lifestyle/news/g4266/iceland-crystal-ice-caves/ https://www.newzealand.com/uk/waitomo-caves/ http://www.geologypage.com/2016/06/cave-of-crystals-giant-crystal-cave.html https://www.chinadiscovery.com/guangxi/guilin/reed-flute-cave.html https://www.gotobermuda.com/article/the-natural-wonder-bermudas-crystal-caves https://www.nationalgeographic.com/science/2007/04/giant-crystal-cave-mexico-mystery-solved/