ナショナルジオグラフィックさんのインスタグラム写真 - (ナショナルジオグラフィックInstagram)「Photos by Robbie Shone @shonephoto | An area of Lechuguilla Cave, in Carlsbad Caverns National Park, known as Pearlsian Gulf was named after several nests of pristine white cave pearls. These pearls are formed when saturated water drips into small pools with such vigor that regular speleothems like stalagmites can't form. A bit of foreign matter such as a grain of sand becomes coated with calcite, and these slight movements of water help keep the sand oscillating as new layers of calcite are added, and eventually a pristine white cave pearl is formed.」2月11日 0時48分